Effects of Dietary Black Soldier Fly (Hermetia illucens) Oil Supplementation on Flesh Quality of Largemouth Bass (Micropterus salmoides)

Black soldier fly (Hermetia illucens) larvae are a promising source of insect oil, characterized by rapid fatty acid accumulation and a high lauric acid content. This study investigated the effects of dietary black soldier fly oil (BSFO) on muscle quality in largemouth bass (Micropterus salmoides). Experimental diets were formulated to be isonitrogenous, isolipidic, and isophosphoric, with 1.0% and 2.0% BSFO partially replacing soybean oil. A control group received 2.3% soybean oil without BSFO or glycerol monolaurate (GML), while positive controls were supplemented with 0.35% and 0.7% GML. Fish (initial weight: 25.08 ± 0.12 g) were cultured in pond cages for 56 days.Muscle quality and nutritional traits were evaluated, including proximate composition, fatty acid profiles, texture properties, fiber diameter, hydroxyproline content, antioxidant capacity, and expression of genes related to muscle development, atrophy, apoptosis, and mTOR signaling. Compared with the control, the 2.0% BSFO group showed a significant increase in muscle hydroxyproline content (p < 0.05), while GML supplementation led to a significant decrease (p 0.05), but n-3/n-6 PUFA ratio and HUFA levels were significantly elevated (p < 0.05). The dietary supplementation of BSFO enhanced the levels of high-quality fatty acids in the muscle tissue. Antioxidant capacity was also significantly enhanced in the 1.0% BSFO group (p < 0.05), but reduced in the GML groups (p < 0.05). Texture analysis showed that BSFO significantly improved muscle hardness, elasticity, chewiness, and gumminess (p < 0.05). Gene expression analysis revealed no significant effects of BSFO on genes related to myogenesis（myod、myog）and muscle atrophy（mstn, murf1）, or apoptosis-related genes (caspase8, caspase9, caspase3) (p > 0.05); mTOR signaling pathway-related genes (s6k1, akt1) were significantly upregulated in the 2.0% BSFO group (p < 0.05). In contrast, 0.7% GML significantly upregulated genes related to myogenesis（myod, myf5, myog）, muscle atrophy（mstn, fbxo32, murf1）, and apoptosis (caspase8, caspase9, caspase3) (p < 0.05). In summary, dietary supplementation with 1.0% BSFO effectively enhances muscle quality in largemouth bass without negatively impacting muscle development.