Predation preference of the crayfish Procambarus clarkii on schistosomiasis vector snails: influence of snail species, infection status, and size

Predation preference of the crayfish Procambarus clarkii on schistosomiasis vector snails: influence of snail species, infection status, and size | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Predation preference of the crayfish Procambarus clarkii on schistosomiasis vector snails: influence of snail species, infection status, and size Geoffrey Maina, Nicolaus Mbugi, Protus Omondi, Wolfgang Richard Mukabana, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9078344/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 11 You are reading this latest preprint version Abstract Background Schistosomiasis control relies largely on preventive chemotherapy; however, rapid reinfection persists in many endemic settings due to continued transmission by freshwater snail intermediate hosts. Biological control using natural predators has been proposed as a complementary strategy to reduce vector snail populations. The invasive North American crayfish Procambarus clarkii , which preys on schistosome-transmitting snails, represents a promising candidate. However, the ecological and biological factors influencing predator–prey interactions between crayfish and vector snails remain poorly understood. Methods We evaluated the predatory potential of Procambarus clarkii on schistosomiasis vector snails under controlled laboratory conditions. Aquarium-based experiments examined predator–prey interactions involving crayfish and snail hosts ( Biomphalaria and Bulinus spp.). Experiments assessed the effects of snail species, infection status, prey size, and crayfish developmental stage (juvenile and adult) on predation dynamics. Predation outcomes were assessed using cumulative predation and time-to-depletion analyses. Results In early-time cumulative predation analysis, infected snails were consumed more frequently than uninfected snails (64.3% vs. 35.7%; exact binomial test, p = 0.044). Time-to-depletion analysis also showed earlier clearance of infected snails (median 18 h vs. 20 h; paired Wilcoxon signed-rank test, p = 0.002). In species comparison experiments, Biomphalaria snails were depleted more rapidly than Bulinus , with complete consumption of Biomphalaria (5/5 snails) observed in all replicate tanks within 48 h. Size-dependent assays showed that adult P. clarkii consumed larger snails more frequently than smaller snails. In predator–prey stage experiments, adult crayfish consumed similar proportions of adult and juvenile snails (82.8% vs. 80.6%), whereas juvenile crayfish consumed significantly more juvenile than adult snails (63/180 vs. 10/180; p < 0.001). Conclusion Predation by Procambarus clarkii on schistosomiasis vector snails is influenced by snail infection status, species identity, prey size, and predator developmental stage. These findings provide experimental evidence supporting the potential role of crayfish as a complementary biological control agent within integrated schistosomiasis control strategies. Procambarus clarkii predation Biomphalaria Bulinus schistosomiasis biological control Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Introduction Schistosomiasis remains one of the most important neglected tropical diseases worldwide, affecting over 250 million people globally in 2024, with more than 90% of all cases occur in Africa [ 1 ]. Human infection occurs when cercariae released from infected snails penetrate the skin during contact with contaminated water. The two main schistosome species that infect human beings in Africa are Schistosoma mansoni , which causes intestinal and hepatic schistosomiasis, and Schistosoma haematobium , which causes urogenital schistosomiasis[ 2 ]. Control efforts have historically focused on preventive chemotherapy using praziquantel delivered through mass drug administration (MDA) programs targeting high-risk populations such as school-aged children[ 3 ]. While this strategy has substantially reduced disease morbidity in many endemic settings, it does not interrupt transmission because it does not target the parasite stages within the intermediate snail hosts[ 4 , 5 ]. Consequently, reinfection remains common in endemic areas, particularly where environmental conditions support persistent snail populations[ 6 – 8 ]. Additional challenges, including sustainability, incomplete treatment coverage, treatment non-compliance, and concerns about potential drug resistance, highlight the need for complementary control strategies that target other components of the parasite life cycle[ 9 , 10 ]. Vector and intermediate host control is among the strategies advocated by the World Health Organisation (WHO) in the fight against Neglected Tropical Diseases such as schistosomiasis[ 11 , 12 ]. Chemical molluscicides were widely used to reduce snail populations; however, their application has declined due to concerns regarding cost, environmental toxicity, effects on non-target organisms, and the rapid recolonization of treated habitats[ 13 , 14 ]. These limitations have renewed interest in environmentally sustainable approaches such as biological control. Biological control strategies exploit natural ecological interactions to suppress vector populations and may involve predators, competitors, or other ecological mechanisms that limit the survival or reproduction of intermediate host snails. Among potential biological control agents, freshwater crustaceans such as crayfish have attracted increasing attention because of their ability to prey on aquatic invertebrates, including snails that transmit schistosomiasis. The red swamp crayfish, Procambarus clarkii , is a freshwater decapod native to North America that has been widely introduced into some aquatic ecosystems around the world Kenya[ 15 , 16 ]. This species is highly adaptable and omnivorous, feeding on a wide range of benthic organisms including mollusks, insect larvae, and aquatic vegetation[ 17 ]. Field studies in Kenya have demonstrated that crayfish can exert strong predatory pressure on freshwater snail populations, suggesting their role in regulating intermediate host populations for schistosomiasis in natural aquatic ecosystems[ 17 – 19 ]. Our previous ecological study conducted in the Mwea irrigation scheme in central Kenya an area characterized by high schistosomiasis prevalence and heavy infestation of schistosome-transmitting snails demonstrated that the invasive crayfish Procambarus clarkii had established within the irrigation ecosystem and was associated with reduced densities of vector snails, including Biomphalaria pfeifferi and Bulinus , the two most common shistosome transmitting snails in Kenya. Importantly, the study also showed that predator–prey dynamics between crayfish and vector snails were strongly influenced by environmental and ecological factors, including water flow, vegetation cover, habitat disturbance, and seasonal variability. These findings provided ecological evidence supporting the hypothesis that P. clarkii may contribute to the suppression of schistosomiasis vector snails in endemic aquatic environments, while highlighting the complexity of predator–prey interactions under natural conditions[ 19 ]. However, field-based observations alone cannot fully elucidate the biological mechanisms governing these interactions. To better understand the factors that determine snail susceptibility to predation, controlled experimental studies are necessary. In the present study, we experimentally evaluated key biological characteristics that may influence predation by P. clarkii . Specifically, we assessed (i) differential predation between infected and uninfected snails; (ii) the relative susceptibility of Biomphalaria and Bulinus species, the predominant schistosomiasis vector snails in Kenyan endemic settings; (iii) the influence of snail size classes on predation susceptibility; and (iv) predation efficiency across different crayfish life stages (juvenile and adult) and snail developmental stages. By experimentally quantifying these predator–prey interactions under controlled laboratory conditions, this study provides mechanistic evidence that complements previous field observations and further evaluates the potential role of crayfish as a complementary biological control agent within integrated schistosomiasis control strategies in endemic settings. Methods Study sites and crayfish collection Crayfish used as predators in this study were collected from two irrigation canal sites in the Mwea rice irrigation scheme, Kenya: Nice (0°39′58.30′S, 37°21′45.38′E; altitude 1,145 m) and Nguka Canal (0°38′38.55′S, 37°18′17.72′E; altitude 1,180 m). Sampling was conducted in April and August 2022. Crayfish were captured by hand-scooping along rice canals containing macrophytes or by baited onion-bag traps (Fig. 1 ). Sampling sites were selected based on our previous studies of aquatic fauna in the area and accessibility[ 19 ]. Each site was mapped and subdivided into two sampling stations. After collection, crayfish were transferred into plastic pails containing damp vegetation to prevent desiccation. At the end of each sampling day, individuals were pooled into perforated buckets containing moist vegetation and secured with lids to prevent escape. This precaution was necessary because crayfish are nocturnal and highly active in darkness [ 20 ] Collected crayfish were transported to the Kenya Medical Research Institute (KEMRI) snail rearing facility in Nairobi under cool conditions with damp vegetation to maximize survival. Laboratory maintenance of crayfish In the laboratory, crayfish were measured using Vernier calipers (Mitutoyo Corporation, Japan) to determine total length (TL) and carapace length (CL) (Fig. 2 A). Individuals were categorized into two size classes: juveniles (approximately 40 mm TL) and adults (approximately 65 mm TL). Crayfish were maintained in aerated mesocosm aquaria (90 × 60 × 40 cm; approximately 10 L water volume) for acclimation. Aquaria were prepared two days prior to introducing the animals. Decaying wooden planks and water hyacinth roots were placed in tanks to provide shelter and reduce aggressive interactions such as fighting, mutilation, or cannibalism. Crayfish were fed daily with commercial fish food (Worldwide Aquatics, Premium Tropical Fish Food, Arvin, CA, USA) and also grazed on water hyacinth roots (Fig. 2 ). Mean aquarium conditions were maintained at 24.8°C, pH 7.51, and salinity of 0.06 ppt. The snail rearing room temperature was maintained at approximately 28°C using fan heaters. Prior to predation experiments, crayfish were starved for 48 hours to standardize hunger levels. Snail collection and maintenance Snails used as prey were collected from the Asao River (0°17′5″S, 34°55′17″E). Two medically important freshwater snail taxa were used: Biomphalaria pfeifferi and Bulinus spp. Previous surveys suggest that crayfish are absent from this habitat, indicating that collected snails were unlikely to have experienced prior exposure to crayfish predation [ 21 – 23 ]. Approximately 400 Biomphalaria and 200 Bulinus snails were collected using long-handled scoops fitted with a 2 × 2 mm mesh sieve. Snails were transported to the KEMRI laboratories in open containers covered with aquatic vegetation. In the laboratory, snails were separated by species and maintained in aerated aquaria (50 L) under the same environmental conditions used for crayfish (pH 7.51, temperature 28°C, salinity 0.06 ppt). Aquarium water was replaced biweekly using a siphon system fitted with a sieve to prevent snail loss. Screening for cercarial shedding To identify infected snails, all collected individuals were screened for cercarial shedding. Snails were individually exposed to natural light for three hours (09:00–12:00) in 24-well plates to stimulate cercarial emergence. Cercariae were examined using a dissecting microscope. This procedure was repeated weekly for 30 days to ensure detection of pre-patent infections. Snails confirmed to be shedding cercariae were classified as infected and used in predation experiments comparing infected and uninfected snails. Predation experiments Predation experiments were conducted in glass aquaria with a single crayfish per tank, which constituted the experimental unit. Snails were measured using Vernier calipers prior to experiments. Shell diameter was measured for Biomphalaria snails and aperture height for Bulinus snails following established malacological protocols[ 24 ] Snails were grouped into size classes to minimize confounding effects of shell morphology: small (5–7 mm), medium (6.5–9 mm), and large (7–13.5 mm). Individual experiments examined different aspects of predator–prey interactions, including predation by infection status, species comparison, and size-dependent susceptibility to predation. Differential predation by infection status To assess whether infected snails were more susceptible to predation, naturally infected and uninfected Biomphalaria snails were used. Snails were gently dried with paper towels and marked with nail varnish to allow identification during experiments. Red varnish was applied to infected snails and white varnish to uninfected snails (Fig. 3 ). Marked snails were allowed to dry for five minutes before introduction into aquaria. Each aquarium received 10 snails (five infected and five uninfected) with an average shell diameter of approximately 10 mm. One adult crayfish (TL = 65 mm; CL = 45 mm) was introduced per tank. Multiple replicate tanks were established. Snail consumption was recorded at regular time intervals to quantify predation dynamics. Species comparison experiment To compare predation between snail species, equal numbers of Biomphalaria and Bulinus snails were introduced into experimental aquaria containing a single crayfish. Consumption was recorded over a 48-hour period to determine whether predation differed between species. Size-dependent predation experiments Size-dependent predation was examined in experiments comparing small (3–6 mm) and large (7–10 mm) snails. In each experiment, crayfish were exposed to snails of the two size classes in replicate aquaria to determine whether prey size influenced predation rates. Observations were recorded at regular intervals, and the number of snails consumed from each size class was documented. In addition, we evaluated the influence of predator and prey developmental stage on predation dynamics. Juvenile P. clarkii (total length = 40 mm; carapace length = 25 mm) and adult P. clarkii (total length = 65 mm; carapace length = 45 mm) were used as predators. These were exposed to juvenile snails (= 4 mm shell diameter) and adult snails (= 10 mm shell diameter), representing the typical immature and mature stages of snail hosts commonly encountered in natural freshwater habitats. Statistical analysis All analyses were conducted using R version 4.5.2. Continuous variables are reported as mean ± standard deviation (SD) unless otherwise stated. Statistical significance was defined as α = 0.05. The experimental unit of replication was the individual crayfish (one crayfish per tank). Control tanks without crayfish were excluded from inferential analyses. Because complete prey depletion occurred in several experiments, primary analyses were restricted to the earliest post-baseline time point within each experiment to minimize bias arising from ceiling effects. For experiments with only two observation time points, the first post-baseline observation was used as the primary endpoint. To evaluate differential predation by infection status, two complementary outcomes were analyzed. First, early-time cumulative consumption pooled across replicates was evaluated using an exact binomial test against the null hypothesis of equal predation probability (0.5). Second, time-to-depletion was defined as the time (hours) required for all snails within a given infection group to be consumed. Depletion times for positive and negative snail groups were compared using a paired Wilcoxon signed-rank test (one-sided). For the species comparison experiment, analysis was performed at 48 hours by calculating the mean number of snails consumed per crayfish for Biomphalaria and Bulinus. Because outcomes were identical across replicates (resulting in zero variance), formal hypothesis testing was not performed and results are presented descriptively. For the snail size–dependent predation experiments, the mean number of snails consumed per crayfish was calculated at the earliest post-baseline time point for each experiment (17 h and 24 h, respectively). Because outcomes were identical across replicates, statistical hypothesis testing was not informative; therefore, results are presented descriptively as effect sizes. For the adult versus juvenile crayfish experiment, early-time cumulative predation was calculated by pooling the number of snails consumed across replicate tanks at the earliest post-baseline observation. Differences in predation between adult and juvenile snail groups were evaluated separately for adult and juvenile crayfish using exact binomial tests against the null hypothesis of equal predation probability (0.5). In addition, time-to-depletion was defined as the time required for all snails of a given size class within a tank to be consumed, and depletion times were compared within crayfish size using paired Wilcoxon signed-rank tests. RESULTS Study design and experimental characteristics Across experiments, replication was defined at the level of the individual crayfish (one crayfish per tank). Experiments were conducted between March and November 2023. A total of 4 crayfish were used in the August 2023 experiment, 5 in June–July 2023, 4 in March–May 2023, and 9 in November 2023 (three replicates of three crayfish each). Crayfish size was standardized within each experiment. Mean total length (TL) and carapace length (CL) were 40.0 ± 0.0 mm and 25.0 ± 0.0 mm, respectively, in the March–May and August experiments, and 65.0 ± 0.0 mm and 40.0–45.0 ± 0.0 mm in the June–July and November experiments. The absence of within-experiment variation reflects the use of uniform size classes by design. Snail sizes differed among experiments according to the experimental objective. Mean snail size ranged from 5.0 ± 2.05 mm in the June–July experiment to 10.0 ± 0.0 mm in the November experiment. In size-comparison experiments, discrete non-overlapping size classes were used (3 mm vs 7 mm; 7 mm vs 10 mm). Initial snail densities per crayfish were fixed within experiments: 2 per size class in March–May, 3–4 per size class in June–July, 5 per species in August, and 4 per infection category in November. This standardized prey density ensured comparability across replicate crayfish within each experimental block. Table 1 summarizes the design and experimental characteristics across the four laboratory predation experiments. Table 1 Design and experimental characteristics across the four laboratory predation experiments Experiment N crayfish N tanks Timepoints Crayfish TL (mm) mean ± SD Crayfish CL (mm) mean ± SD Snail size (mm) mean ± SD Initial snails per group mean ± SD August 2023 4 4 2 40.0 ± 0.0 25.0 ± 0.0 10.0 ± 2.07 5.0 ± 0.0 June–July 2023 5 5 2 65.0 ± 0.0 40.0 ± 0.0 5.0 ± 2.05 3.5 ± 0.53 March–May 2023 4 4 2 40.0 ± 0.0 25.0 ± 0.0 8.5 ± 1.55 2.0 ± 0.0 November 2023 9 3 5 65.0 ± 0.0 45.0 ± 0.0 10.0 ± 0.0 4.0 ± 0.0 Differential predation between infected and non-infected Crayfish exhibited differential predation between positive and negative snail groups. At the earliest post-baseline pooled observation across replicates (n = 5), crayfish consumed 27 positive and 15 negative snails, corresponding to 64.3% of consumed prey being positive (Fig. 4 B). An exact binomial test indicated that positive snails were consumed more frequently than expected under equal predation probability ( p = 0.044). Temporal depletion dynamics further illustrated this pattern, with the number of remaining snails declining more rapidly in the positive group over time (Fig. 4 A). Consistent with this trend, time-to-depletion analysis showed earlier depletion of positive snails compared with negative snails (median 18 h vs. 20 h; paired Wilcoxon signed-rank test, p = 0.002; Fig. 2 C). (B) Early-time cumulative consumption pooled across replicates at the earliest post-baseline observation. Positive snails accounted for 64.3% of consumed prey (exact binomial test, one-sided p = 0.044). (C) Paired comparison of time to depletion within each crayfish. Positive snails were depleted earlier than negative snails (median 18 h vs 20 h; paired Wilcoxon test, p = 0.002). Species comparison : Biomphalaria vs Bulinus In the species Comparison experiment, crayfish exhibited differential depletion between Biomphalaria and Bulinus snails. By 48 h, 100% depletion of Biomphalaria (5/5 snails) was observed in all replicate crayfish (n = 5), whereas one Bulinus snail remained in each tank (4/5 consumed) (Fig. 5 ). Because outcomes were identical across replicates, statistical hypothesis testing was not informative. Nevertheless, the consistent difference of one additional snail consumed per crayfish indicates greater depletion of Biomphalaria under these laboratory conditions. Size-dependent predation Size-dependent predation patterns were observed in both size-comparison experiments. In the first experiment, the mean number of larger snails (7 mm) consumed was approximately twice that of smaller snails (3 mm) within 17 h. Across all replicate crayfish (n = 5), consumption was 4/4 for 7 mm snails compared with 2/4 for 3 mm snails, corresponding to a twofold difference in the number of snails consumed per crayfish between the two size classes (Fig. 6 A). In the second experiment, which compared larger snail size classes, predation also differed by size. By 24 h, the mean number of 7 mm snails consumed was more than half that of 10 mm snails. All replicate crayfish (n = 5) consumed 100% (2/2) of the 7 mm snails in each replicate, whereas only one of the two 10 mm snails was consumed in each replicate (Fig. 6 B). Predator size and prey size interaction Predation patterns differed between adult and juvenile crayfish. At the earliest post-baseline observation, adult crayfish consumed similar proportions of adult and juvenile snails, with 149/180 adult snails (82.8%) and 145/180 juvenile snails (80.6%) consumed across pooled replicate tanks (Fig. 7 A). An exact binomial test indicated no evidence of differential early-time predation between the 2 snail stages under adult crayfish predation (p = 0.861). In contrast, juvenile crayfish consumed juvenile snails more frequently than adult snails. Across pooled replicate tanks, juvenile crayfish consumed 63/180 juvenile snails (35.0%) compared with only 10/180 adult snails (5.6%). This difference was strongly supported by an exact binomial test (p < 0.001). Time-to-depletion analysis showed a similar pattern. Under adult crayfish predation, depletion times did not differ significantly between adult and juvenile snails (paired Wilcoxon signed-rank test, p = 0.345) (Fig. 7 B). However, under juvenile crayfish predation, juvenile snails were depleted significantly earlier than adult snails (Fig. 7 C) (paired Wilcoxon signed-rank test, p = 0.0036). Together, these findings indicate that juvenile crayfish were more effective against smaller snails, whereas adult crayfish preyed efficiently on both snail size classes without clear early-time selectivity. Discussion In the present study, we evaluated the predatory potential of the invasive crayfish Procambarus clarkii as a biological control agent for schistosomiasis-transmitting snails in Kenya. This work aimed to generate evidence for ecological strategies that could complement preventive chemotherapy, particularly praziquantel-based mass drug administration programs. Such complementary approaches are increasingly important in settings where schistosomiasis transmission persists despite repeated treatment campaigns. To our knowledge, this study is among the few laboratory investigations to simultaneously examine how snail infection status, species identity, prey size, and predator developmental stage influence crayfish predation dynamics relevant to schistosomiasis transmission. Our results first demonstrated differential predation between infected and uninfected snails. Infected snails were consumed more frequently and depleted earlier than uninfected snails. This pattern may reflect parasite-induced physiological or behavioral changes in infected hosts. Parasite infection is known to weaken snail hosts and can reduce locomotion and anti-predatory responses, thereby increasing vulnerability to predators. Similar mechanisms have been reported in other predator-parasite systems, where predators preferentially remove infected individuals from host populations [ 25 ]. Previous studies have also shown that infected snails may exhibit reduced movement and impaired escape responses, increasing susceptibility to predation [ 26 , 27 ]. Preferential removal of infected snails could have epidemiological implications, as it may reduce the number of parasite-releasing individuals within transmission sites. Species-specific differences in predation were also observed. In our experiments, Biomphalaria snails were consistently depleted more rapidly than Bulinus . Differences in susceptibility between snail species may reflect variation in shell morphology, mobility, or behavioral responses. Planorbid snails such as Biomphalaria typically possess flatter shells and tend to move slowly along the substrate, potentially making them easier targets for benthic predators. In contrast, Bulinus snails were frequently observed climbing aquarium walls, suggesting behavioral avoidance that may reduce predation risk. Similar species-specific patterns have been reported previously. For example, Khalil and Sleem [ 28 ] documented predation of several snail species by crayfish in irrigation canals in Egypt, including Biomphalaria alexandrina , Bulinus truncatus , and Lymnaea natalensis , with substantial reductions in vector snail populations. Prey size also influenced predation outcomes in our experiments. Adult crayfish showed the highest predation on intermediate-sized Biomphalaria snails (7 mm), compared with smaller individuals (3 mm) or the largest size class (10 mm).This pattern may be partly explained by the morphological characteristics of crayfish chelae, which become larger and stronger as crayfish mature, enabling them to handle larger prey more effectively. Similar patterns have been reported in aquatic predator–prey systems where prey size strongly influences feeding relationships [ 29 – 31 ]. These findings suggest that prey size is an important determinant of snail vulnerability to crayfish predation. Predation patterns were further influenced by the interaction between predator size and prey size. Adult crayfish demonstrated strong predatory capacity against both juvenile and adult snails, consuming similar proportions of both size classes. In contrast, juvenile crayfish preferentially consumed juvenile snails and were far less effective against larger snails. These findings are consistent with optimal foraging theory, which predicts that predators select prey sizes that maximize energetic profitability while minimizing handling difficulty [ 32 ]. Similar relationships between predator body size and prey size selection have also been documented in several crayfish species [ 33 – 35 ]. Together, these results suggest that larger crayfish may play a particularly important role in suppressing snail populations across multiple size classes in natural ecosystems. Despite these promising findings, several limitations should be considered when interpreting the results. First, the experiments were conducted under controlled laboratory conditions that may not fully replicate the ecological complexity of natural freshwater habitats. Environmental factors such as habitat structure, water flow, vegetation cover, and alternative prey availability could influence predator–prey interactions in the field. Second, the use of nail varnish to distinguish infected from uninfected snails may have introduced visual or chemical cues that could potentially influence predator behavior. Although care was taken to minimize such effects, the possibility that marking influenced predation cannot be completely excluded. Future research should therefore focus on evaluating crayfish–snail interactions under natural field conditions, particularly in irrigation canals and other aquatic habitats where schistosomiasis transmission occurs. Field-based studies will be important to determine whether predator-mediated reductions in snail populations can translate into measurable reductions in parasite transmission. Overall, this study demonstrates that predation by Procambarus clarkii on schistosomiasis vector snails is influenced by multiple ecological and biological factors, including snail infection status, species identity, prey size, and predator developmental stage. These findings provide experimental evidence supporting the potential role of crayfish as a complementary biological control agent within integrated schistosomiasis control strategies. Conclusion These findings highlight the importance of predator–prey biological characteristics in shaping the predation dynamics of the crayfish Procambarus clarkii and provide insights into how this strategy could be optimized as a biological control approach in endemic settings. The higher vulnerability of infected snails, together with differences in predation among snail species and size classes, suggests that crayfish predation could selectively reduce populations of highly susceptible snail hosts in endemic habitats. Declarations Competing interests All authors have declared no competing of interest. Funding This work was supported by an internal research grant from the Kenya Medical Research Institute (KEMRI) awarded to G.M. (KEMRI/CONF/FIN/6/101) for research on the biological control of schistosomiasis. In addition, G.M. received support for a PhD program at the University of Nairobi. Author Contribution G.M.: Conceptualization, methodology, formal analysis, data curation, writing original draft preparation, and writing, review and editing. N.O.M.: data curation, writing, review and editing. P.O.: Formal analysis, writing, review and editing. W.R.M.: Study design, statistical analysis, manuscript review and editing, and supervision. D.O.: Study design, manuscript review and editing, and supervision. E.A.L.: Data analysis and interpretation, guidance, and critical review of the manuscript. All authors read and approved the final manuscript. Acknowledgement We thank the Kenya Medical Research Institute, Center for Biotechnology, Research and Development, and the Mwea field station for hosting our experiments and providing all the required resources, especially Dr. Martin Mutuku, Ibrahim Mwangi, Joseph Kinuthia, and Celestine Kwoba for help with both fieldwork and project management. Data Availability Data for the present study is available from the corresponding author upon request. References World Health Organisation. 2023. Schistosomiasis Fact Sheet.. https://www.who.int/news-room/fact-sheets/detail/schistosomiasis . Buonfrate D, Ferrari TCA, Adegnika AA, Stothard JR, Gobbi FG. Human schistosomiasis. The Lancet. Elsevier; 2025;405:658–70. Helminth control in school-age children: a guide for managers of control programmes.World Health Organization, Geneva, 2011 Anderson R, Farrell S, Turner H, Walson J, Donnelly CA, Truscott J. 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National Academy of Sciences; 2018;115:E584–91. Organization WH. Field use of molluscicides in schistosomiasis control programmes: an operational manual for programme managers. World Health Organization; 2017 [cited 2026 Mar 10]; https://iris.who.int/bitstream/handle/10665/254641/9789241511995-eng.pdf . Accessed 10 Mar 2026 Organization WH. WHO guideline on control and elimination of human schistosomiasis [Internet]. World Health Organization; 2022 [cited 2026 Mar 10]. https://books.google.com/books?hl=en& lr=&id=DXVyEAAAQBAJ&oi=fnd&pg=PR5&dq=WHO.+2017.+Field+use+of+molluscicides+in+schistosomiasis+control+programmes.&ots=h46mH9kL0D&sig=WzcigLb0kfUMfsBjn5daBbAvecg. Accessed 10 Mar 2026 Moustafa MA, Mossalem HS, Sarhan RM, Abdel-Rahman AA, Hassan EM. The potential effects of silver and gold nanoparticles as molluscicides and cercaricides on Schistosoma mansoni. Parasitol Res. 2018;117:3867–80. https://doi.org/10.1007/s00436-018-6093-2 Ibrahim AM, Abdel-Ghaffar FA, Hassan HA-M, Fol MF. Assessment of molluscicidal and larvicidal activities of CuO nanoparticles on Biomphalaria alexandrina snails. Beni-Suef Univ J Basic Appl Sci. 2022;11:84. https://doi.org/10.1186/s43088-022-00264-6 Hofkin BV, Hofinger DM, Koech DK, Loker ES. Predation of Biomphalaria and non-target molluscs by the crayfish Procambarus clarkii : implications for the biological control of schistosomiasis. Ann Trop Med Parasitol. 1992;86:663–70. https://doi.org/10.1080/00034983.1992.11812723 Hofkin BV, Mkoji GM, Koech DK, Loker ES. Control of schistosome-transmitting snails in Kenya by the North American crayfish Procambarus clarkii. Am J Trop Med Hyg. 1991;45:339–44. Monde C, Syampungani S, Rico A, Van Den Brink P. The potential for using red claw crayfish and hybrid African catfish as biological control agents for Schistosoma host snails. Afr J Aquat Sci. 2017;42:235–43. https://doi.org/10.2989/16085914.2017.1373245 Hofkin BV, Koech DK, Oumaj J, Loker ES. The North American crayfish Procambarus clarkii and the biological control of schistosome-transmitting snails in Kenya: laboratory and field investigations. Biol Control. Elsevier; 1991;1:183–7. Maina GM, Mbugi N, Mukabana WR, Odongo DO, Lelo EA. Harnessing crayfish, Procambarus clarkii, to eliminate Schistosome transmitting snails in the Mwea irrigation scheme, Kenya. Helminthologia. 2025;62:241. Thomas JR, James J, Newman RC, Riley WD, Griffiths SW, Cable J. The impact of streetlights on an aquatic invasive species: Artificial light at night alters signal crayfish behaviour. Appl Anim Behav Sci. Elsevier; 2016;176:143–9. Mutuku MW, Dweni CK, Mwangi M, Kinuthia JM, Mwangi IN, Maina GM, et al. Field-derived Schistosoma mansoni and Biomphalaria pfeifferi in Kenya: a compatible association characterized by lack of strong local adaptation, and presence of some snails able to persistently produce cercariae for over a year. Parasit Vectors. 2014;7:533. https://doi.org/10.1186/s13071-014-0533-3 Laidemitt MR, Gleichsner AM, Ingram CD, Gay SD, Reinhart EM, Mutuku MW, et al. Host preference of field-derived Schistosoma mansoni is influenced by snail host compatibility and infection status. Ecosphere. 2022;13:e4004. https://doi.org/10.1002/ecs2.4004 Steinauer ML, Mwangi IN, Maina GM, Kinuthia JM, Mutuku MW, Agola EL, et al. Interactions between natural populations of human and rodent schistosomes in the Lake Victoria region of Kenya: a molecular epidemiological approach. PLoS Negl Trop Dis. Public Library of Science San Francisco, USA; 2008;2:e222. Brown DS. Freshwater snails of Africa and their medical importance [Internet]. CRC press; 1994 [cited 2026 Mar 10]. https://api.taylorfrancis.com/content/books/mono/download?identifierName=doi&identifierValue=10.1201/ 9781482295184&type=googlepdf. Accessed 10 Mar 2026 Rohr JR, Civitello DJ, Crumrine PW, Halstead NT, Miller AD, Schotthoefer AM, et al. Predator diversity, intraguild predation, and indirect effects drive parasite transmission. Proc Natl Acad Sci. 2015;112:3008–13. https://doi.org/10.1073/pnas.1415971112 Sokolow SH, Lafferty KD, Kuris AM. Regulation of laboratory populations of snails (Biomphalaria and Bulinus spp.) by river prawns, Macrobrachium spp.(Decapoda, Palaemonidae): implications for control of schistosomiasis. Acta Trop. Elsevier; 2014;132:64–74. Swartz SJ, De Leo GA, Wood CL, Sokolow SH. Infection with schistosome parasites in snails leads to increased predation by prawns: implications for human schistosomiasis control. J Exp Biol. The Company of Biologists; 2015;218:3962–7. Khalil MT, Sleem SH. Can the freshwater crayfish eradicate schistosomiasis in Egypt and Africa. J Am Sci. 2011;7:457–62. Blanchard JL. Body size and ecosystem dynamics: an introduction. Oikos [Internet]. 2011 [cited 2026 Mar 10];120. https://search.ebscohost.com/login.aspx?direct=true &profile=ehost&scope=site&authtype=crawler&jrnl=00301299&asa=N&AN=59527220&h=veQZmS%2Fwotj%2FDTv%2BoFiVzscuK08hVEsrSpmLv983qJ2BVPIHHroabvHAIMiMPPPQcWL9FFwmB%2BO7Tzy2iiFBRA%3D%3D&crl=c. Accessed 10 Mar 2026 Brose U. Body-mass constraints on foraging behaviour determine population and food‐web dynamics. Funct Ecol. 2010;24:28–34. https://doi.org/10.1111/j.1365-2435.2009.01618.x Yvon-Durocher G, Reiss J, Blanchard J, Ebenman B, Perkins DM, Reuman DC, et al. Across ecosystem comparisons of size structure: methods, approaches and prospects. Oikos. 2011;120:550–63. https://doi.org/10.1111/j.1600-0706.2010.18863.x Curio E. The ethology of predation [Internet]. Springer Science & Business Media; 2012 [cited 2026 Mar 10]. https://books.google.com/books?hl=en &lr=&id=N5n-CAAAQBAJ&oi=fnd&pg=PA1&dq=CURIO,+E.+2012.+The+Ethology+of+Predation+(Zoophysiology+and+Ecology,+Vol.+7).+Springer+Science+%26+Business+Media,+Berlin,+Germany,+252+p.&ots=3C9-MqSlVt&sig=anX168wP41otifY0UOHz8zLsS1I. Accessed 10 Mar 2026 Barnes C, Maxwell D, Reuman DC, Jennings S. Global patterns in predator–prey size relationships reveal size dependency of trophic transfer efficiency. Ecology. 2010;91:222–32. https://doi.org/10.1890/08-2061.1 Olden JD, Larson ER, Mims MC. Home-field advantage: native signal crayfish (Pacifastacus leniusculus) out consume newly introduced crayfishes for invasive Chinese mystery snail (Bellamya chinensis). Aquat Ecol. Springer; 2009;43:1073–84. Babbitt CR. UNRAVELING THE COMPLEX INTERACTIONS BETWEEN MEMBERS OF THE SCHISTOSOMA HAEMATOBIUM GROUP AND BULINUS SNAILS IN AND AROUND LAKE VICTORIA IN WEST KENYA. 2022 [cited 2026 Mar 10]; https://digitalrepository.unm.edu/cgi/viewcontent.cgi?article=1406&context=biol_etds . Accessed 10 Mar 2026 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 25 Mar, 2026 Reviews received at journal 25 Mar, 2026 Reviews received at journal 24 Mar, 2026 Reviews received at journal 20 Mar, 2026 Reviewers agreed at journal 16 Mar, 2026 Reviewers agreed at journal 12 Mar, 2026 Reviewers agreed at journal 12 Mar, 2026 Reviewers invited by journal 12 Mar, 2026 Editor assigned by journal 11 Mar, 2026 Submission checks completed at journal 11 Mar, 2026 First submitted to journal 09 Mar, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9078344","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":606819120,"identity":"2d425c4d-bde4-4d2f-9479-b089222c73ae","order_by":0,"name":"Geoffrey Maina","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA2ElEQVRIiWNgGAWjYJCCAwwMNgZQBgODBJFa0kjUAgSHDeBMglrkww4/PFxQc96YX+zswwMMv2wYJNsb8GsxvJ1mcHjGsdtmkrPTDQ4w9qUxSPMcIKBldoLBYR622zYGt9MYDjD2HGaQk0ggpCX9w2Gef+ds7OFa5B8Q8It0jsFh3rYDZgbSQC0MPw4zSBPyv4F0TsFh3r5kYwmQLYkNaTySPQQcJj87ffNnnm92hv2z05g/fPhjIydx/AABW1DkE9sYeAg4C2hLAwr3D0ENo2AUjIJRMAIBALrKRN1hypCDAAAAAElFTkSuQmCC","orcid":"","institution":"Kenya Medical Research Institute","correspondingAuthor":true,"prefix":"","firstName":"Geoffrey","middleName":"","lastName":"Maina","suffix":""},{"id":606819121,"identity":"506e333d-07be-40c7-85e1-f92881b2f27a","order_by":1,"name":"Nicolaus Mbugi","email":"","orcid":"","institution":"Mbeya university of Science and Technology (MUST)","correspondingAuthor":false,"prefix":"","firstName":"Nicolaus","middleName":"","lastName":"Mbugi","suffix":""},{"id":606819122,"identity":"61cbf095-904d-439b-8b1f-ae770076649e","order_by":2,"name":"Protus Omondi","email":"","orcid":"","institution":"Mount Kenya University","correspondingAuthor":false,"prefix":"","firstName":"Protus","middleName":"","lastName":"Omondi","suffix":""},{"id":606819123,"identity":"fa34750a-e5a7-4658-9d9a-cafcca7610ea","order_by":3,"name":"Wolfgang Richard Mukabana","email":"","orcid":"","institution":"University of Nairobi","correspondingAuthor":false,"prefix":"","firstName":"Wolfgang","middleName":"Richard","lastName":"Mukabana","suffix":""},{"id":606819124,"identity":"b37a5933-f20e-4492-87b3-25272fd00483","order_by":4,"name":"David Onyango Odongo","email":"","orcid":"","institution":"University of Nairobi","correspondingAuthor":false,"prefix":"","firstName":"David","middleName":"Onyango","lastName":"Odongo","suffix":""},{"id":606819125,"identity":"23b46838-b1bf-49d7-be53-3db4b7d065ed","order_by":5,"name":"Eric Agola Lelo","email":"","orcid":"","institution":"Kenya Medical Research Institute","correspondingAuthor":false,"prefix":"","firstName":"Eric","middleName":"Agola","lastName":"Lelo","suffix":""}],"badges":[],"createdAt":"2026-03-10 02:54:10","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9078344/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9078344/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":104926768,"identity":"779cf8cf-c90b-4566-be82-e90390b6528c","added_by":"auto","created_at":"2026-03-18 19:25:54","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":244998,"visible":true,"origin":"","legend":"\u003cp\u003eTrapping of crayfish using onion bag traps\u003c/p\u003e","description":"","filename":"image1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9078344/v1/0b0242a24c054362f8316f01.jpeg"},{"id":104926762,"identity":"1cad763b-9f68-4eb6-9c85-61913a754c9d","added_by":"auto","created_at":"2026-03-18 19:25:53","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":244420,"visible":true,"origin":"","legend":"\u003cp\u003eSome activities performed over the course of the present study, (A) determination of the crayfish sizes and (B) Experimental setup for the disparate assays\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-9078344/v1/24befcfb7f0432808bca174e.png"},{"id":104926767,"identity":"869e9ac1-0623-417b-937a-a2f1c772c55b","added_by":"auto","created_at":"2026-03-18 19:25:53","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":285124,"visible":true,"origin":"","legend":"\u003cp\u003edrying of paints used to discriminate positive and negative snails; Red nail and white cutex indicating positive and negative snails respectively\u003c/p\u003e","description":"","filename":"image3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9078344/v1/9430250d7b3aec0196e990b9.jpeg"},{"id":104926764,"identity":"128ed343-8b53-4c64-a589-fdb5b01477d1","added_by":"auto","created_at":"2026-03-18 19:25:53","extension":"jpeg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":148272,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eDifferential predation between positive and negative snail groups\u003c/strong\u003e. (A) Mean (±SE) number of snails remaining per crayfish over time.\u003cbr\u003e\n(B) Early-time cumulative consumption pooled across replicates at the earliest post-baseline observation. Positive snails accounted for 64.3% of consumed prey (exact binomial test, one-sided p = 0.044). (C) Paired comparison of time to depletion within each crayfish. Positive snails were depleted earlier than negative snails (median 18 h vs 20 h; paired Wilcoxon test, p = 0.002).\u003c/p\u003e","description":"","filename":"image4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9078344/v1/9e74de87dd9dbcd50d89213d.jpeg"},{"id":104926763,"identity":"01c9e0ce-948d-4467-a72a-48e2e687d3e7","added_by":"auto","created_at":"2026-03-18 19:25:53","extension":"jpeg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":83851,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSpecies-specific predation by crayfish\u003c/strong\u003e. Mean number of snails consumed per crayfish at 48 h is shown for \u003cem\u003eBiomphalaria\u003c/em\u003e and \u003cem\u003eBulinus\u003c/em\u003e. All replicate crayfish (n = 4) completely consumed \u003cem\u003eBiomphalaria\u003c/em\u003e (5/5) while leaving one \u003cem\u003eBulinus\u003c/em\u003e snail per tank (4/5 consumed). Error bars denote SE.\u003c/p\u003e","description":"","filename":"image6.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9078344/v1/b1aa9c2517da0288a4ede205.jpeg"},{"id":104926769,"identity":"9ebb784a-1533-4d96-b06f-cce8e5ed5dc2","added_by":"auto","created_at":"2026-03-18 19:25:54","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":88799,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSize-dependent predation by crayfish on \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eBiomphalaria\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e snails.\u003c/strong\u003e (A) June–July 2023 experiment showing mean number of snails consumed per crayfish at 17 h for 3 mm and 7 mm snails. (B) March–May 2023 experiment showing mean number of snails consumed per crayfish at 24 h for 7 mm and 10 mm snails. Error bars denote SE.\u003c/p\u003e","description":"","filename":"image7.png","url":"https://assets-eu.researchsquare.com/files/rs-9078344/v1/0a9f13c48b8f09986d57254e.png"},{"id":104926766,"identity":"50452494-157c-4d29-8b11-2c80fa19834c","added_by":"auto","created_at":"2026-03-18 19:25:53","extension":"jpeg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":248158,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePredator–prey size interactions between crayfish and schistosomiasis vector snails.\u003c/strong\u003e (A) Early-time cumulative predation pooled across replicate tanks at the earliest post-baseline observation. (B) Time to depletion of adult and juvenile snails within tanks under adult and juvenile crayfish predation; lines connect paired observations within tanks. (C) Mean number of snails remaining per tank (±SE) over time for adult snails (10 mm shell diameter) and juvenile snails (4 mm) exposed to adult crayfish (total length 65 mm; carapace length 45 mm) and juvenile crayfish (total length 40 mm; carapace length 25 mm).\u003c/p\u003e","description":"","filename":"image8.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9078344/v1/4bb754e6a1c55a78548c5393.jpeg"},{"id":105034519,"identity":"6c540373-2b4c-45fc-a0eb-c6c90c0a9885","added_by":"auto","created_at":"2026-03-20 07:23:28","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2379563,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9078344/v1/f04569b4-6f3a-4bd6-8721-225fa23d341a.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Predation preference of the crayfish Procambarus clarkii on schistosomiasis vector snails: influence of snail species, infection status, and size","fulltext":[{"header":"Introduction","content":"\u003cp\u003eSchistosomiasis remains one of the most important neglected tropical diseases worldwide, affecting over 250\u0026nbsp;million people globally in 2024, with more than 90% of all cases occur in Africa [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Human infection occurs when cercariae released from infected snails penetrate the skin during contact with contaminated water. The two main schistosome species that infect human beings in Africa are \u003cem\u003eSchistosoma mansoni\u003c/em\u003e, which causes intestinal and hepatic schistosomiasis, and \u003cem\u003eSchistosoma haematobium\u003c/em\u003e, which causes urogenital schistosomiasis[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eControl efforts have historically focused on preventive chemotherapy using praziquantel delivered through mass drug administration (MDA) programs targeting high-risk populations such as school-aged children[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. While this strategy has substantially reduced disease morbidity in many endemic settings, it does not interrupt transmission because it does not target the parasite stages within the intermediate snail hosts[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Consequently, reinfection remains common in endemic areas, particularly where environmental conditions support persistent snail populations[\u003cspan additionalcitationids=\"CR7\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Additional challenges, including sustainability, incomplete treatment coverage, treatment non-compliance, and concerns about potential drug resistance, highlight the need for complementary control strategies that target other components of the parasite life cycle[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eVector and intermediate host control is among the strategies advocated by the World Health Organisation (WHO) in the fight against Neglected Tropical Diseases such as schistosomiasis[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Chemical molluscicides were widely used to reduce snail populations; however, their application has declined due to concerns regarding cost, environmental toxicity, effects on non-target organisms, and the rapid recolonization of treated habitats[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. These limitations have renewed interest in environmentally sustainable approaches such as biological control. Biological control strategies exploit natural ecological interactions to suppress vector populations and may involve predators, competitors, or other ecological mechanisms that limit the survival or reproduction of intermediate host snails.\u003c/p\u003e \u003cp\u003eAmong potential biological control agents, freshwater crustaceans such as crayfish have attracted increasing attention because of their ability to prey on aquatic invertebrates, including snails that transmit schistosomiasis. The red swamp crayfish, \u003cem\u003eProcambarus clarkii\u003c/em\u003e, is a freshwater decapod native to North America that has been widely introduced into some aquatic ecosystems around the world Kenya[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. This species is highly adaptable and omnivorous, feeding on a wide range of benthic organisms including mollusks, insect larvae, and aquatic vegetation[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Field studies in Kenya have demonstrated that crayfish can exert strong predatory pressure on freshwater snail populations, suggesting their role in regulating intermediate host populations for schistosomiasis in natural aquatic ecosystems[\u003cspan additionalcitationids=\"CR18\" citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eOur previous ecological study conducted in the Mwea irrigation scheme in central Kenya an area characterized by high schistosomiasis prevalence and heavy infestation of schistosome-transmitting snails demonstrated that the invasive crayfish \u003cem\u003eProcambarus clarkii\u003c/em\u003e had established within the irrigation ecosystem and was associated with reduced densities of vector snails, including \u003cem\u003eBiomphalaria pfeifferi\u003c/em\u003e and \u003cem\u003eBulinus\u003c/em\u003e, the two most common shistosome transmitting snails in Kenya. Importantly, the study also showed that predator\u0026ndash;prey dynamics between crayfish and vector snails were strongly influenced by environmental and ecological factors, including water flow, vegetation cover, habitat disturbance, and seasonal variability. These findings provided ecological evidence supporting the hypothesis that \u003cem\u003eP. clarkii\u003c/em\u003e may contribute to the suppression of schistosomiasis vector snails in endemic aquatic environments, while highlighting the complexity of predator\u0026ndash;prey interactions under natural conditions[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eHowever, field-based observations alone cannot fully elucidate the biological mechanisms governing these interactions. To better understand the factors that determine snail susceptibility to predation, controlled experimental studies are necessary. In the present study, we experimentally evaluated key biological characteristics that may influence predation by \u003cem\u003eP. clarkii\u003c/em\u003e. Specifically, we assessed (i) differential predation between infected and uninfected snails; (ii) the relative susceptibility of \u003cem\u003eBiomphalaria\u003c/em\u003e and \u003cem\u003eBulinus\u003c/em\u003e species, the predominant schistosomiasis vector snails in Kenyan endemic settings; (iii) the influence of snail size classes on predation susceptibility; and (iv) predation efficiency across different crayfish life stages (juvenile and adult) and snail developmental stages. By experimentally quantifying these predator\u0026ndash;prey interactions under controlled laboratory conditions, this study provides mechanistic evidence that complements previous field observations and further evaluates the potential role of crayfish as a complementary biological control agent within integrated schistosomiasis control strategies in endemic settings.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStudy sites and crayfish collection\u003c/h2\u003e \u003cp\u003eCrayfish used as predators in this study were collected from two irrigation canal sites in the Mwea rice irrigation scheme, Kenya: Nice (0\u0026deg;39\u0026prime;58.30\u0026prime;S, 37\u0026deg;21\u0026prime;45.38\u0026prime;E; altitude 1,145 m) and Nguka Canal (0\u0026deg;38\u0026prime;38.55\u0026prime;S, 37\u0026deg;18\u0026prime;17.72\u0026prime;E; altitude 1,180 m). Sampling was conducted in April and August 2022. Crayfish were captured by hand-scooping along rice canals containing macrophytes or by baited onion-bag traps (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Sampling sites were selected based on our previous studies of aquatic fauna in the area and accessibility[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eEach site was mapped and subdivided into two sampling stations. After collection, crayfish were transferred into plastic pails containing damp vegetation to prevent desiccation. At the end of each sampling day, individuals were pooled into perforated buckets containing moist vegetation and secured with lids to prevent escape. This precaution was necessary because crayfish are nocturnal and highly active in darkness [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]\u003c/p\u003e \u003cp\u003eCollected crayfish were transported to the Kenya Medical Research Institute (KEMRI) snail rearing facility in Nairobi under cool conditions with damp vegetation to maximize survival.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eLaboratory maintenance of crayfish\u003c/h3\u003e\n\u003cp\u003eIn the laboratory, crayfish were measured using Vernier calipers (Mitutoyo Corporation, Japan) to determine total length (TL) and carapace length (CL) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA). Individuals were categorized into two size classes: juveniles (approximately 40 mm TL) and adults (approximately 65 mm TL).\u003c/p\u003e \u003cp\u003eCrayfish were maintained in aerated mesocosm aquaria (90 \u0026times; 60 \u0026times; 40 cm; approximately 10 L water volume) for acclimation. Aquaria were prepared two days prior to introducing the animals. Decaying wooden planks and water hyacinth roots were placed in tanks to provide shelter and reduce aggressive interactions such as fighting, mutilation, or cannibalism.\u003c/p\u003e \u003cp\u003eCrayfish were fed daily with commercial fish food (Worldwide Aquatics, Premium Tropical Fish Food, Arvin, CA, USA) and also grazed on water hyacinth roots (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Mean aquarium conditions were maintained at 24.8\u0026deg;C, pH 7.51, and salinity of 0.06 ppt. The snail rearing room temperature was maintained at approximately 28\u0026deg;C using fan heaters. Prior to predation experiments, crayfish were starved for 48 hours to standardize hunger levels.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eSnail collection and maintenance\u003c/h3\u003e\n\u003cp\u003eSnails used as prey were collected from the Asao River (0\u0026deg;17\u0026prime;5\u0026Prime;S, 34\u0026deg;55\u0026prime;17\u0026Prime;E). Two medically important freshwater snail taxa were used: \u003cem\u003eBiomphalaria pfeifferi\u003c/em\u003e and \u003cem\u003eBulinus\u003c/em\u003e spp. Previous surveys suggest that crayfish are absent from this habitat, indicating that collected snails were unlikely to have experienced prior exposure to crayfish predation [\u003cspan additionalcitationids=\"CR22\" citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eApproximately 400 \u003cem\u003eBiomphalaria\u003c/em\u003e and 200 \u003cem\u003eBulinus\u003c/em\u003e snails were collected using long-handled scoops fitted with a 2 \u0026times; 2 mm mesh sieve. Snails were transported to the KEMRI laboratories in open containers covered with aquatic vegetation. In the laboratory, snails were separated by species and maintained in aerated aquaria (50 L) under the same environmental conditions used for crayfish (pH 7.51, temperature 28\u0026deg;C, salinity 0.06 ppt). Aquarium water was replaced biweekly using a siphon system fitted with a sieve to prevent snail loss.\u003c/p\u003e\n\u003ch3\u003eScreening for cercarial shedding\u003c/h3\u003e\n\u003cp\u003eTo identify infected snails, all collected individuals were screened for cercarial shedding. Snails were individually exposed to natural light for three hours (09:00\u0026ndash;12:00) in 24-well plates to stimulate cercarial emergence. Cercariae were examined using a dissecting microscope. This procedure was repeated weekly for 30 days to ensure detection of pre-patent infections. Snails confirmed to be shedding cercariae were classified as infected and used in predation experiments comparing infected and uninfected snails.\u003c/p\u003e\n\u003ch3\u003ePredation experiments\u003c/h3\u003e\n\u003cp\u003ePredation experiments were conducted in glass aquaria with a single crayfish per tank, which constituted the experimental unit. Snails were measured using Vernier calipers prior to experiments. Shell diameter was measured for \u003cem\u003eBiomphalaria\u003c/em\u003e snails and aperture height for \u003cem\u003eBulinus\u003c/em\u003e snails following established malacological protocols[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]\u003c/p\u003e \u003cp\u003eSnails were grouped into size classes to minimize confounding effects of shell morphology: small (5\u0026ndash;7 mm), medium (6.5\u0026ndash;9 mm), and large (7\u0026ndash;13.5 mm). Individual experiments examined different aspects of predator\u0026ndash;prey interactions, including predation by infection status, species comparison, and size-dependent susceptibility to predation.\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eDifferential predation by infection status\u003c/h2\u003e \u003cp\u003eTo assess whether infected snails were more susceptible to predation, naturally infected and uninfected \u003cem\u003eBiomphalaria\u003c/em\u003e snails were used. Snails were gently dried with paper towels and marked with nail varnish to allow identification during experiments. Red varnish was applied to infected snails and white varnish to uninfected snails (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Marked snails were allowed to dry for five minutes before introduction into aquaria.\u003c/p\u003e \u003cp\u003eEach aquarium received 10 snails (five infected and five uninfected) with an average shell diameter of approximately 10 mm. One adult crayfish (TL\u0026thinsp;=\u0026thinsp;65 mm; CL\u0026thinsp;=\u0026thinsp;45 mm) was introduced per tank. Multiple replicate tanks were established. Snail consumption was recorded at regular time intervals to quantify predation dynamics.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eSpecies comparison experiment\u003c/h3\u003e\n\u003cp\u003eTo compare predation between snail species, equal numbers of \u003cem\u003eBiomphalaria\u003c/em\u003e and \u003cem\u003eBulinus\u003c/em\u003e snails were introduced into experimental aquaria containing a single crayfish. Consumption was recorded over a 48-hour period to determine whether predation differed between species.\u003c/p\u003e\n\u003ch3\u003eSize-dependent predation experiments\u003c/h3\u003e\n\u003cp\u003eSize-dependent predation was examined in experiments comparing small (3\u0026ndash;6 mm) and large (7\u0026ndash;10 mm) snails. In each experiment, crayfish were exposed to snails of the two size classes in replicate aquaria to determine whether prey size influenced predation rates. Observations were recorded at regular intervals, and the number of snails consumed from each size class was documented.\u003c/p\u003e \u003cp\u003eIn addition, we evaluated the influence of predator and prey developmental stage on predation dynamics. Juvenile \u003cem\u003eP. clarkii\u003c/em\u003e (total length\u0026thinsp;=\u0026thinsp;40 mm; carapace length\u0026thinsp;=\u0026thinsp;25 mm) and adult \u003cem\u003eP. clarkii\u003c/em\u003e (total length\u0026thinsp;=\u0026thinsp;65 mm; carapace length\u0026thinsp;=\u0026thinsp;45 mm) were used as predators. These were exposed to juvenile snails (=\u0026thinsp;4 mm shell diameter) and adult snails (=\u0026thinsp;10 mm shell diameter), representing the typical immature and mature stages of snail hosts commonly encountered in natural freshwater habitats.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analysis\u003c/h2\u003e \u003cp\u003eAll analyses were conducted using R version 4.5.2. Continuous variables are reported as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation (SD) unless otherwise stated. Statistical significance was defined as α\u0026thinsp;=\u0026thinsp;0.05.\u003c/p\u003e \u003cp\u003eThe experimental unit of replication was the individual crayfish (one crayfish per tank). Control tanks without crayfish were excluded from inferential analyses. Because complete prey depletion occurred in several experiments, primary analyses were restricted to the earliest post-baseline time point within each experiment to minimize bias arising from ceiling effects. For experiments with only two observation time points, the first post-baseline observation was used as the primary endpoint.\u003c/p\u003e \u003cp\u003eTo evaluate differential predation by infection status, two complementary outcomes were analyzed. First, early-time cumulative consumption pooled across replicates was evaluated using an exact binomial test against the null hypothesis of equal predation probability (0.5). Second, time-to-depletion was defined as the time (hours) required for all snails within a given infection group to be consumed. Depletion times for positive and negative snail groups were compared using a paired Wilcoxon signed-rank test (one-sided).\u003c/p\u003e \u003cp\u003eFor the species comparison experiment, analysis was performed at 48 hours by calculating the mean number of snails consumed per crayfish for Biomphalaria and Bulinus. Because outcomes were identical across replicates (resulting in zero variance), formal hypothesis testing was not performed and results are presented descriptively.\u003c/p\u003e \u003cp\u003eFor the snail size\u0026ndash;dependent predation experiments, the mean number of snails consumed per crayfish was calculated at the earliest post-baseline time point for each experiment (17 h and 24 h, respectively). Because outcomes were identical across replicates, statistical hypothesis testing was not informative; therefore, results are presented descriptively as effect sizes.\u003c/p\u003e \u003cp\u003eFor the adult versus juvenile crayfish experiment, early-time cumulative predation was calculated by pooling the number of snails consumed across replicate tanks at the earliest post-baseline observation. Differences in predation between adult and juvenile snail groups were evaluated separately for adult and juvenile crayfish using exact binomial tests against the null hypothesis of equal predation probability (0.5). In addition, time-to-depletion was defined as the time required for all snails of a given size class within a tank to be consumed, and depletion times were compared within crayfish size using paired Wilcoxon signed-rank tests.\u003c/p\u003e \u003c/div\u003e"},{"header":"RESULTS","content":"\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eStudy design and experimental characteristics\u003c/h2\u003e \u003cp\u003eAcross experiments, replication was defined at the level of the individual crayfish (one crayfish per tank). Experiments were conducted between March and November 2023. A total of 4 crayfish were used in the August 2023 experiment, 5 in June\u0026ndash;July 2023, 4 in March\u0026ndash;May 2023, and 9 in November 2023 (three replicates of three crayfish each).\u003c/p\u003e \u003cp\u003eCrayfish size was standardized within each experiment. Mean total length (TL) and carapace length (CL) were 40.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.0 mm and 25.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.0 mm, respectively, in the March\u0026ndash;May and August experiments, and 65.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.0 mm and 40.0\u0026ndash;45.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.0 mm in the June\u0026ndash;July and November experiments. The absence of within-experiment variation reflects the use of uniform size classes by design.\u003c/p\u003e \u003cp\u003eSnail sizes differed among experiments according to the experimental objective. Mean snail size ranged from 5.0\u0026thinsp;\u0026plusmn;\u0026thinsp;2.05 mm in the June\u0026ndash;July experiment to 10.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.0 mm in the November experiment. In size-comparison experiments, discrete non-overlapping size classes were used (3 mm vs 7 mm; 7 mm vs 10 mm).\u003c/p\u003e \u003cp\u003eInitial snail densities per crayfish were fixed within experiments: 2 per size class in March\u0026ndash;May, 3\u0026ndash;4 per size class in June\u0026ndash;July, 5 per species in August, and 4 per infection category in November. This standardized prey density ensured comparability across replicate crayfish within each experimental block. Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e summarizes the design and experimental characteristics across the four laboratory predation experiments.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003e\u003cb\u003eDesign and experimental characteristics across the four laboratory predation experiments\u003c/b\u003e\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"8\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eExperiment\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eN crayfish\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eN tanks\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eTimepoints\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCrayfish TL (mm) mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eCrayfish CL (mm) mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eSnail size (mm) mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eInitial snails per group mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAugust 2023\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e40.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e25.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e10.0\u0026thinsp;\u0026plusmn;\u0026thinsp;2.07\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c8\"\u003e \u003cp\u003e5.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eJune\u0026ndash;July 2023\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e65.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e40.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e5.0\u0026thinsp;\u0026plusmn;\u0026thinsp;2.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c8\"\u003e \u003cp\u003e3.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.53\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMarch\u0026ndash;May 2023\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e40.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e25.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e8.5\u0026thinsp;\u0026plusmn;\u0026thinsp;1.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c8\"\u003e \u003cp\u003e2.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNovember 2023\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e65.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e45.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e10.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c8\"\u003e \u003cp\u003e4.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eDifferential predation between infected and non-infected\u003c/h2\u003e \u003cp\u003eCrayfish exhibited differential predation between positive and negative snail groups. At the earliest post-baseline pooled observation across replicates (n\u0026thinsp;=\u0026thinsp;5), crayfish consumed 27 positive and 15 negative snails, corresponding to 64.3% of consumed prey being positive (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eB). An exact binomial test indicated that positive snails were consumed more frequently than expected under equal predation probability (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.044).\u003c/p\u003e \u003cp\u003eTemporal depletion dynamics further illustrated this pattern, with the number of remaining snails declining more rapidly in the positive group over time (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA). Consistent with this trend, time-to-depletion analysis showed earlier depletion of positive snails compared with negative snails (median 18 h vs. 20 h; paired Wilcoxon signed-rank test, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.002; Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eC).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e(B) Early-time cumulative consumption pooled across replicates at the earliest post-baseline observation. Positive snails accounted for 64.3% of consumed prey (exact binomial test, one-sided p\u0026thinsp;=\u0026thinsp;0.044). (C) Paired comparison of time to depletion within each crayfish. Positive snails were depleted earlier than negative snails (median 18 h vs 20 h; paired Wilcoxon test, p\u0026thinsp;=\u0026thinsp;0.002).\u003c/p\u003e \u003cp\u003e \u003cb\u003eSpecies comparison\u003c/b\u003e: \u003cb\u003eBiomphalaria\u003c/b\u003e \u003cb\u003evs\u003c/b\u003e \u003cb\u003eBulinus\u003c/b\u003e\u003c/p\u003e \u003cp\u003eIn the species Comparison experiment, crayfish exhibited differential depletion between \u003cem\u003eBiomphalaria\u003c/em\u003e and \u003cem\u003eBulinus\u003c/em\u003e snails. By 48 h, 100% depletion of \u003cem\u003eBiomphalaria\u003c/em\u003e (5/5 snails) was observed in all replicate crayfish (n\u0026thinsp;=\u0026thinsp;5), whereas one \u003cem\u003eBulinus\u003c/em\u003e snail remained in each tank (4/5 consumed) (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). Because outcomes were identical across replicates, statistical hypothesis testing was not informative. Nevertheless, the consistent difference of one additional snail consumed per crayfish indicates greater depletion of \u003cem\u003eBiomphalaria\u003c/em\u003e under these laboratory conditions.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eSize-dependent predation\u003c/h2\u003e \u003cp\u003eSize-dependent predation patterns were observed in both size-comparison experiments. In the first experiment, the mean number of larger snails (7 mm) consumed was approximately twice that of smaller snails (3 mm) within 17 h. Across all replicate crayfish (n\u0026thinsp;=\u0026thinsp;5), consumption was 4/4 for 7 mm snails compared with 2/4 for 3 mm snails, corresponding to a twofold difference in the number of snails consumed per crayfish between the two size classes (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eA).\u003c/p\u003e \u003cp\u003eIn the second experiment, which compared larger snail size classes, predation also differed by size. By 24 h, the mean number of 7 mm snails consumed was more than half that of 10 mm snails. All replicate crayfish (n\u0026thinsp;=\u0026thinsp;5) consumed 100% (2/2) of the 7 mm snails in each replicate, whereas only one of the two 10 mm snails was consumed in each replicate (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eB).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003ePredator size and prey size interaction\u003c/h2\u003e \u003cp\u003ePredation patterns differed between adult and juvenile crayfish. At the earliest post-baseline observation, adult crayfish consumed similar proportions of adult and juvenile snails, with 149/180 adult snails (82.8%) and 145/180 juvenile snails (80.6%) consumed across pooled replicate tanks (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eA). An exact binomial test indicated no evidence of differential early-time predation between the 2 snail stages under adult crayfish predation (p\u0026thinsp;=\u0026thinsp;0.861). In contrast, juvenile crayfish consumed juvenile snails more frequently than adult snails. Across pooled replicate tanks, juvenile crayfish consumed 63/180 juvenile snails (35.0%) compared with only 10/180 adult snails (5.6%). This difference was strongly supported by an exact binomial test (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001).\u003c/p\u003e \u003cp\u003eTime-to-depletion analysis showed a similar pattern. Under adult crayfish predation, depletion times did not differ significantly between adult and juvenile snails (paired Wilcoxon signed-rank test, p\u0026thinsp;=\u0026thinsp;0.345) (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eB). However, under juvenile crayfish predation, juvenile snails were depleted significantly earlier than adult snails (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eC) (paired Wilcoxon signed-rank test, p\u0026thinsp;=\u0026thinsp;0.0036). Together, these findings indicate that juvenile crayfish were more effective against smaller snails, whereas adult crayfish preyed efficiently on both snail size classes without clear early-time selectivity.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn the present study, we evaluated the predatory potential of the invasive crayfish \u003cem\u003eProcambarus clarkii\u003c/em\u003e as a biological control agent for schistosomiasis-transmitting snails in Kenya. This work aimed to generate evidence for ecological strategies that could complement preventive chemotherapy, particularly praziquantel-based mass drug administration programs. Such complementary approaches are increasingly important in settings where schistosomiasis transmission persists despite repeated treatment campaigns. To our knowledge, this study is among the few laboratory investigations to simultaneously examine how snail infection status, species identity, prey size, and predator developmental stage influence crayfish predation dynamics relevant to schistosomiasis transmission.\u003c/p\u003e \u003cp\u003eOur results first demonstrated differential predation between infected and uninfected snails. Infected snails were consumed more frequently and depleted earlier than uninfected snails. This pattern may reflect parasite-induced physiological or behavioral changes in infected hosts. Parasite infection is known to weaken snail hosts and can reduce locomotion and anti-predatory responses, thereby increasing vulnerability to predators. Similar mechanisms have been reported in other predator-parasite systems, where predators preferentially remove infected individuals from host populations [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Previous studies have also shown that infected snails may exhibit reduced movement and impaired escape responses, increasing susceptibility to predation [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Preferential removal of infected snails could have epidemiological implications, as it may reduce the number of parasite-releasing individuals within transmission sites.\u003c/p\u003e \u003cp\u003eSpecies-specific differences in predation were also observed. In our experiments, \u003cem\u003eBiomphalaria\u003c/em\u003e snails were consistently depleted more rapidly than \u003cem\u003eBulinus\u003c/em\u003e. Differences in susceptibility between snail species may reflect variation in shell morphology, mobility, or behavioral responses. Planorbid snails such as \u003cem\u003eBiomphalaria\u003c/em\u003e typically possess flatter shells and tend to move slowly along the substrate, potentially making them easier targets for benthic predators. In contrast, \u003cem\u003eBulinus\u003c/em\u003e snails were frequently observed climbing aquarium walls, suggesting behavioral avoidance that may reduce predation risk. Similar species-specific patterns have been reported previously. For example, Khalil and Sleem [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e] documented predation of several snail species by crayfish in irrigation canals in Egypt, including \u003cem\u003eBiomphalaria alexandrina\u003c/em\u003e, \u003cem\u003eBulinus truncatus\u003c/em\u003e, and \u003cem\u003eLymnaea natalensis\u003c/em\u003e, with substantial reductions in vector snail populations.\u003c/p\u003e \u003cp\u003ePrey size also influenced predation outcomes in our experiments. Adult crayfish showed the highest predation on intermediate-sized \u003cem\u003eBiomphalaria\u003c/em\u003e snails (7 mm), compared with smaller individuals (3 mm) or the largest size class (10 mm).This pattern may be partly explained by the morphological characteristics of crayfish chelae, which become larger and stronger as crayfish mature, enabling them to handle larger prey more effectively. Similar patterns have been reported in aquatic predator\u0026ndash;prey systems where prey size strongly influences feeding relationships [\u003cspan additionalcitationids=\"CR30\" citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. These findings suggest that prey size is an important determinant of snail vulnerability to crayfish predation.\u003c/p\u003e \u003cp\u003ePredation patterns were further influenced by the interaction between predator size and prey size. Adult crayfish demonstrated strong predatory capacity against both juvenile and adult snails, consuming similar proportions of both size classes. In contrast, juvenile crayfish preferentially consumed juvenile snails and were far less effective against larger snails. These findings are consistent with optimal foraging theory, which predicts that predators select prey sizes that maximize energetic profitability while minimizing handling difficulty [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. Similar relationships between predator body size and prey size selection have also been documented in several crayfish species [\u003cspan additionalcitationids=\"CR34\" citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. Together, these results suggest that larger crayfish may play a particularly important role in suppressing snail populations across multiple size classes in natural ecosystems.\u003c/p\u003e \u003cp\u003eDespite these promising findings, several limitations should be considered when interpreting the results. First, the experiments were conducted under controlled laboratory conditions that may not fully replicate the ecological complexity of natural freshwater habitats. Environmental factors such as habitat structure, water flow, vegetation cover, and alternative prey availability could influence predator\u0026ndash;prey interactions in the field. Second, the use of nail varnish to distinguish infected from uninfected snails may have introduced visual or chemical cues that could potentially influence predator behavior. Although care was taken to minimize such effects, the possibility that marking influenced predation cannot be completely excluded.\u003c/p\u003e \u003cp\u003eFuture research should therefore focus on evaluating crayfish\u0026ndash;snail interactions under natural field conditions, particularly in irrigation canals and other aquatic habitats where schistosomiasis transmission occurs. Field-based studies will be important to determine whether predator-mediated reductions in snail populations can translate into measurable reductions in parasite transmission.\u003c/p\u003e \u003cp\u003eOverall, this study demonstrates that predation by \u003cem\u003eProcambarus clarkii\u003c/em\u003e on schistosomiasis vector snails is influenced by multiple ecological and biological factors, including snail infection status, species identity, prey size, and predator developmental stage. These findings provide experimental evidence supporting the potential role of crayfish as a complementary biological control agent within integrated schistosomiasis control strategies.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThese findings highlight the importance of predator\u0026ndash;prey biological characteristics in shaping the predation dynamics of the crayfish \u003cem\u003eProcambarus clarkii\u003c/em\u003e and provide insights into how this strategy could be optimized as a biological control approach in endemic settings. The higher vulnerability of infected snails, together with differences in predation among snail species and size classes, suggests that crayfish predation could selectively reduce populations of highly susceptible snail hosts in endemic habitats.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003cstrong\u003eCompeting interests\u003c/strong\u003e \u003cp\u003eAll authors have declared no competing of interest.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eThis work was supported by an internal research grant from the Kenya Medical Research Institute (KEMRI) awarded to G.M. (KEMRI/CONF/FIN/6/101) for research on the biological control of schistosomiasis. In addition, G.M. received support for a PhD program at the University of Nairobi.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eG.M.: Conceptualization, methodology, formal analysis, data curation, writing original draft preparation, and writing, review and editing. N.O.M.: data curation, writing, review and editing. P.O.: Formal analysis, writing, review and editing. W.R.M.: Study design, statistical analysis, manuscript review and editing, and supervision. D.O.: Study design, manuscript review and editing, and supervision. E.A.L.: Data analysis and interpretation, guidance, and critical review of the manuscript. All authors read and approved the final manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eWe thank the Kenya Medical Research Institute, Center for Biotechnology, Research and Development, and the Mwea field station for hosting our experiments and providing all the required resources, especially Dr. Martin Mutuku, Ibrahim Mwangi, Joseph Kinuthia, and Celestine Kwoba for help with both fieldwork and project management.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eData for the present study is available from the corresponding author upon request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eWorld Health Organisation. 2023. 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Parasit Vectors. 2014;7:533. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1186/s13071-014-0533-3\u003c/span\u003e\u003cspan address=\"10.1186/s13071-014-0533-3\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLaidemitt MR, Gleichsner AM, Ingram CD, Gay SD, Reinhart EM, Mutuku MW, et al. Host preference of field-derived \u003cem\u003eSchistosoma mansoni\u003c/em\u003e is influenced by snail host compatibility and infection status. Ecosphere. 2022;13:e4004. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1002/ecs2.4004\u003c/span\u003e\u003cspan address=\"10.1002/ecs2.4004\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSteinauer ML, Mwangi IN, Maina GM, Kinuthia JM, Mutuku MW, Agola EL, et al. Interactions between natural populations of human and rodent schistosomes in the Lake Victoria region of Kenya: a molecular epidemiological approach. PLoS Negl Trop Dis. Public Library of Science San Francisco, USA; 2008;2:e222.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBrown DS. Freshwater snails of Africa and their medical importance [Internet]. CRC press; 1994 [cited 2026 Mar 10]. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://api.taylorfrancis.com/content/books/mono/download?identifierName=doi\u0026amp;identifierValue=10.1201/\u003c/span\u003e\u003cspan address=\"https://api.taylorfrancis.com/content/books/mono/download?identifierName=doi\u0026amp;identifierValue=10.1201/\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e9781482295184\u0026amp;type=googlepdf. Accessed 10 Mar 2026\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRohr JR, Civitello DJ, Crumrine PW, Halstead NT, Miller AD, Schotthoefer AM, et al. Predator diversity, intraguild predation, and indirect effects drive parasite transmission. Proc Natl Acad Sci. 2015;112:3008\u0026ndash;13. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1073/pnas.1415971112\u003c/span\u003e\u003cspan address=\"10.1073/pnas.1415971112\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSokolow SH, Lafferty KD, Kuris AM. Regulation of laboratory populations of snails (Biomphalaria and Bulinus spp.) by river prawns, Macrobrachium spp.(Decapoda, Palaemonidae): implications for control of schistosomiasis. Acta Trop. Elsevier; 2014;132:64\u0026ndash;74.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSwartz SJ, De Leo GA, Wood CL, Sokolow SH. Infection with schistosome parasites in snails leads to increased predation by prawns: implications for human schistosomiasis control. J Exp Biol. The Company of Biologists; 2015;218:3962\u0026ndash;7.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKhalil MT, Sleem SH. Can the freshwater crayfish eradicate schistosomiasis in Egypt and Africa. J Am Sci. 2011;7:457\u0026ndash;62.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBlanchard JL. Body size and ecosystem dynamics: an introduction. Oikos [Internet]. 2011 [cited 2026 Mar 10];120. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://search.ebscohost.com/login.aspx?direct=true\u003c/span\u003e\u003cspan address=\"https://search.ebscohost.com/login.aspx?direct=true\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u0026amp;profile=ehost\u0026amp;scope=site\u0026amp;authtype=crawler\u0026amp;jrnl=00301299\u0026amp;asa=N\u0026amp;AN=59527220\u0026amp;h=veQZmS%2Fwotj%2FDTv%2BoFiVzscuK08hVEsrSpmLv983qJ2BVPIHHroabvHAIMiMPPPQcWL9FFwmB%2BO7Tzy2iiFBRA%3D%3D\u0026amp;crl=c. Accessed 10 Mar 2026\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBrose U. Body-mass constraints on foraging behaviour determine population and food‐web dynamics. Funct Ecol. 2010;24:28\u0026ndash;34. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1111/j.1365-2435.2009.01618.x\u003c/span\u003e\u003cspan address=\"10.1111/j.1365-2435.2009.01618.x\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYvon-Durocher G, Reiss J, Blanchard J, Ebenman B, Perkins DM, Reuman DC, et al. Across ecosystem comparisons of size structure: methods, approaches and prospects. Oikos. 2011;120:550\u0026ndash;63. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1111/j.1600-0706.2010.18863.x\u003c/span\u003e\u003cspan address=\"10.1111/j.1600-0706.2010.18863.x\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCurio E. The ethology of predation [Internet]. Springer Science \u0026amp; Business Media; 2012 [cited 2026 Mar 10]. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://books.google.com/books?hl=en\u003c/span\u003e\u003cspan address=\"https://books.google.com/books?hl=en\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u0026amp;lr=\u0026amp;id=N5n-CAAAQBAJ\u0026amp;oi=fnd\u0026amp;pg=PA1\u0026amp;dq=CURIO,+E.+2012.+The+Ethology+of+Predation+(Zoophysiology+and+Ecology,+Vol.+7).+Springer+Science+%26+Business+Media,+Berlin,+Germany,+252+p.\u0026amp;ots=3C9-MqSlVt\u0026amp;sig=anX168wP41otifY0UOHz8zLsS1I. Accessed 10 Mar 2026\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBarnes C, Maxwell D, Reuman DC, Jennings S. Global patterns in predator\u0026ndash;prey size relationships reveal size dependency of trophic transfer efficiency. Ecology. 2010;91:222\u0026ndash;32. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1890/08-2061.1\u003c/span\u003e\u003cspan address=\"10.1890/08-2061.1\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eOlden JD, Larson ER, Mims MC. Home-field advantage: native signal crayfish (Pacifastacus leniusculus) out consume newly introduced crayfishes for invasive Chinese mystery snail (Bellamya chinensis). Aquat Ecol. Springer; 2009;43:1073\u0026ndash;84.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBabbitt CR. UNRAVELING THE COMPLEX INTERACTIONS BETWEEN MEMBERS OF THE SCHISTOSOMA HAEMATOBIUM GROUP AND BULINUS SNAILS IN AND AROUND LAKE VICTORIA IN WEST KENYA. 2022 [cited 2026 Mar 10]; \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://digitalrepository.unm.edu/cgi/viewcontent.cgi?article=1406\u0026amp;context=biol_etds\u003c/span\u003e\u003cspan address=\"https://digitalrepository.unm.edu/cgi/viewcontent.cgi?article=1406\u0026amp;context=biol_etds\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e. Accessed 10 Mar 2026\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"tropical-medicine-and-health","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"tmah","sideBox":"Learn more about [Tropical Medicine and Health](https://tropmedhealth.biomedcentral.com/)","snPcode":"41182","submissionUrl":"https://submission.springernature.com/new-submission/41182/3","title":"Tropical Medicine and Health","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Procambarus clarkii, predation, Biomphalaria, Bulinus, schistosomiasis, biological control","lastPublishedDoi":"10.21203/rs.3.rs-9078344/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9078344/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e \u003cp\u003eSchistosomiasis control relies largely on preventive chemotherapy; however, rapid reinfection persists in many endemic settings due to continued transmission by freshwater snail intermediate hosts. Biological control using natural predators has been proposed as a complementary strategy to reduce vector snail populations. The invasive North American crayfish \u003cem\u003eProcambarus clarkii\u003c/em\u003e, which preys on schistosome-transmitting snails, represents a promising candidate. However, the ecological and biological factors influencing predator\u0026ndash;prey interactions between crayfish and vector snails remain poorly understood.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eWe evaluated the predatory potential of \u003cem\u003eProcambarus clarkii\u003c/em\u003e on schistosomiasis vector snails under controlled laboratory conditions. Aquarium-based experiments examined predator\u0026ndash;prey interactions involving crayfish and snail hosts (\u003cem\u003eBiomphalaria\u003c/em\u003e and \u003cem\u003eBulinus\u003c/em\u003e spp.). Experiments assessed the effects of snail species, infection status, prey size, and crayfish developmental stage (juvenile and adult) on predation dynamics. Predation outcomes were assessed using cumulative predation and time-to-depletion analyses.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eIn early-time cumulative predation analysis, infected snails were consumed more frequently than uninfected snails (64.3% vs. 35.7%; exact binomial test, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.044). Time-to-depletion analysis also showed earlier clearance of infected snails (median 18 h vs. 20 h; paired Wilcoxon signed-rank test, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.002). In species comparison experiments, \u003cem\u003eBiomphalaria\u003c/em\u003e snails were depleted more rapidly than \u003cem\u003eBulinus\u003c/em\u003e, with complete consumption of \u003cem\u003eBiomphalaria\u003c/em\u003e (5/5 snails) observed in all replicate tanks within 48 h. Size-dependent assays showed that adult \u003cem\u003eP. clarkii\u003c/em\u003e consumed larger snails more frequently than smaller snails. In predator\u0026ndash;prey stage experiments, adult crayfish consumed similar proportions of adult and juvenile snails (82.8% vs. 80.6%), whereas juvenile crayfish consumed significantly more juvenile than adult snails (63/180 vs. 10/180; \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001).\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e \u003cp\u003ePredation by \u003cem\u003eProcambarus clarkii\u003c/em\u003e on schistosomiasis vector snails is influenced by snail infection status, species identity, prey size, and predator developmental stage. These findings provide experimental evidence supporting the potential role of crayfish as a complementary biological control agent within integrated schistosomiasis control strategies.\u003c/p\u003e","manuscriptTitle":"Predation preference of the crayfish Procambarus clarkii on schistosomiasis vector snails: influence of snail species, infection status, and size","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-03-18 19:25:48","doi":"10.21203/rs.3.rs-9078344/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-03-25T14:26:25+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-03-25T13:09:59+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-03-24T10:54:11+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-03-20T14:33:55+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"183151626817097457632778471414985844898","date":"2026-03-16T10:23:41+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"44698805499239178315739320490009602992","date":"2026-03-12T13:27:38+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"233799995433843477433836939116034197701","date":"2026-03-12T11:37:03+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-03-12T10:53:27+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-03-12T02:50:18+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-03-12T02:50:03+00:00","index":"","fulltext":""},{"type":"submitted","content":"Tropical Medicine and Health","date":"2026-03-10T02:42:13+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"tropical-medicine-and-health","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"tmah","sideBox":"Learn more about [Tropical Medicine and Health](https://tropmedhealth.biomedcentral.com/)","snPcode":"41182","submissionUrl":"https://submission.springernature.com/new-submission/41182/3","title":"Tropical Medicine and Health","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"d16561d0-4d9c-4297-af74-0eef30c9577b","owner":[],"postedDate":"March 18th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-02T12:10:00+00:00","versionOfRecord":[],"versionCreatedAt":"2026-03-18 19:25:48","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9078344","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9078344","identity":"rs-9078344","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}