Insect (black soldier fly larvae) oil as a potential substitute for fish or soy oil in the fish meal-based diet of juvenile rainbow trout (Oncorhynchus mykiss)

Alternative sources of fish oil (FO) are one of the major problems in aquaculture; therefore, the goal of the present study was to examine insect (black soldier fly larvae) oil (BSLO) as a potential replacer of fish/soy oil in juvenile rainbow trout (initial average weight of 32 ± 0.15 g) feed. Four diets were formulated wherein FO (control diet) was completely replaced with either soybean oil (SO) or BSLO, and an additional BSLO-based diet supplemented with 1.5% bile acid (BSLO + BA) were fed to the fish for 10 weeks. Growth performance of the BSLO fed group was similar (P > 0.05) to that of the FO and SO fed groups, however, the fish fed BSLO + BA diet registered the lowest growth (P < 0.05). Oil sources did not (P > 0.05) affect the major nutrient content of whole-body, however, the fatty acid composition of the muscle and liver was influenced (P < 0.05), with the highest 14:0, 16:0, and total saturated fatty acid detected in BSLO or BSLO + BA fed trout compared to the others (P < 0.001). No significant differences were observed in eicosapentaenoic acid + docosahexaenoic acid (EPA + DHA) or total n-3 polyunsaturated fatty acid (PUFA) content in muscle among the groups, whereas, the highest EPA:DHA and n-3:n-6 ratios were detected in the FO group. Gene expression for fatty acid binding protein (fabp), fatty acid synthase (fas), and Δ5 desaturase in the liver was lower in FO (P < 0.05), while BSLO + BA registered the highest Δ6 expression (P = 0.006). Supplementation of BA in the BSLO diet increased superoxide dismutase (SOD) and catalase (CAT) activities compared to the other groups (P < 0.05). In conclusion, BSLO could serve as a substitute for FO and SO in rainbow trout diet without negatively impacting growth performance, whole-body composition and nutrient retention, and modulate the expression of fatty acid metabolism-related genes in rainbow trout.

Insect (black soldier fly, Hermetia illucens) meal supplementation prevents the soybean meal-induced intestinal enteritis in rainbow trout and health benefits of using insect oil

Black solider fly larvae (BSFL) and their oils (BSFLO) are receiving increasing attention as sustainable ingredients in fish feeds, but mostly as replacements to marine sources. There were two aims to this study; in exp. 1, soybean meal (SBM)-based diets were formulated to contain BSFL as supplements at 0 (SBM), 8 (SBM + BSFLlow) or 16% (SBM + BSFLhigh) with a control diet being fishmeal-based (FM). In exp. 2, diets included only fish oil (FO), soybean oil (SBO), BSFLO or BSFLO + bile acid (BA), and all lipid sources were added at 16%. Both experiments were run at the same time and fed to rainbow trout (32 g) with each treatment being triplicated. After 10 weeks the fish were sampled for liver and distal intestine histology, expression of genes responsible for inflammation in the intestine and kidneys, and serum peroxidase and lysozyme activities. In exp. 1, supplementations of BSFL effectively prevented SBM-induced intestinal enteritis, down-regulated intestinal prostaglandin and interferon regulatory factor 1 (IRF-1), while the SBM + BSFLhigh diet significantly increased serum lysozyme activity. In exp. 2, BSFLO caused no histomorphological change to the liver or intestine, but kidney interluekin-8, tumor necrosis factor and IRF-1 were significantly upregulated along with significantly higher serum peroxidase activity. The inclusion of BA in the BSFLO diets significantly upregulated intestinal prostaglandin gene expression. Overall, BSFL supplementations of 8 or 16% prevented SBM-induced intestinal enteritis based on histological observations, which was supported by a down-regulation in pro-inflammatory genes and enhanced innate immunity. Meanwhile, the use of BSFLO showed some immunological benefits. Therefore, these sustainable resources are recommended in the diets of rainbow trout, especially when using elevated levels of plant-based proteins.