Reproductive performance of mangrove crab broodstock, Scylla serrata in a recirculating aquaculture system with polychaete-assisted sand biofilter

Abstract The increasing global demand for mangrove crabs (genus Scylla) and threats to the wild populations highlight the urgency of fully rearing them in captivity. The Southeast Asian Fisheries Development Center/Aquaculture Department (SEAFDEC/AQD) has developed the basic larval rearing and nursery protocols for mangrove crab. However, the supply of hatchery seedstock is still inadequate to meet the requirements for farming. One of the major causes is the inconsistent larval quality in the hatchery which appears to be due to poor broodstock performance. The present study determined the efficiency of two broodstock holding systems, the Recirculating Aquaculture System (RAS) with polychaete-assisted biofilter and the conventional system with regular water replacement or non-RAS (NRAS, control) based on survival rate, spawning, and hatching of Scylla serrata captive broodstock. The percentage survival of mangrove crab broodstock was similar in the RAS (54.00 ± 10.00) and NRAS (50.84 ± 3.89) systems. However, significantly higher mean percentage of spawning (28.61 ± 6.65) and hatching (28.61 ± 6.65) was observed in the RAS compared to the NRAS (15.18 ± 7.41 and 15.18 ± 7.41 respectively). Temperature levels were recorded in the RAS, ranging from 27.7–29.3°C compared to 26.7–28.5°C in the NRAS. Salinity in the RAS ranged from 33.7–35.2 ppt, while in the NRAS it ranged from 33.5–34.7 ppt. Dissolved oxygen (DO) concentrations ranged from 5.8–7.3 mg/L in RAS and 5.5–7.3 in NRAS. Additionally, pH values in the RAS ranged from 7.8–8.6, compared to 7.8–8.5 in the non-RAS. Moreover, ammonia levels were significantly lower in the RAS, ranging from 0.11–0.25 mg/L, compared to 0.31–1.18 mg/L in the NRAS. Similarly, nitrite concentrations were significantly lower in the RAS (0.001–0.007 mg/L) than in the NRAS (0.013–0.026 mg/L). The present study suggests that RAS with polychaete-assisted biofilter offers a less stressful environment thereby enhancing the reproductive performance of Scylla serrata broodstock in captivity.