Alternative sources of fish oil (FO) are one of the major problems in aquaculture and the team of Dr. Vikas Kumar assessed insect (black soldier fly) oil (BSLO) as a potential replacer of fish and soy oil in juvenile rainbow trout 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). Trouts were fed for ten weeks.

The growth performance of the BSLO fed group was similar to the FO and SO fed groups, however, the fish fed BSLO+BA diet registered the lowest growth. Oil sources did not affect the major nutrient content of the whole body, however, the fatty acid composition of the muscle and liver was influenced with the highest 14:0, 16:0 and total saturated fatty acid detected in BSLO or BSLO+BA fed trout compared to the others. No significant differences were observed in eicosapentaenoic acid and docosahexaenoic acid or total n-3 polyunsaturated fatty acid 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. The supplementation of BA in the BSLO diet increased superoxide dismutase and catalase activities compared to the other groups.

Researchers concluded that black soldier fly oil could serve as a substitute for fish oil and soy oil in rainbow trout diets without negatively impacting growth performance, whole-body composition and nutrient retention, and modulate the expression of fatty acid metabolism-related genes in rainbow trout.

Check out the study here.