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)

Abstract

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.

Keywords: Antioxidant enzyme; Fatty acid metabolism; Growth performance; Insect oil; Rainbow trout.

Fig. 1

Principal component (PC) analysis of fatty acids allocation in the liver (L) and muscle (M) of rainbow trout fed with different dietary oil sources for 10 weeks. FO = fish oil; SO = soybean oil; BSLO = black soldier fly larvae oil; BA = bile acid; EPA = eicosapentaenoic acid; DHA = docosahexaenoic acid. Initial average weight of fish is 32 ± 0.0 g.

Fig. 2

Relative mRNA expression of hepatic fatty acid metabolism related genes in rainbow trout fed diets containing fish oil (FO), soybean oil (SO), black soldier fly oil (BSLO), or BSLO + bile acid (BA) for 10 weeks. fabp = fatty acid-binding protein; fas = fatty acid synthase. Different lower case letters within the same gene denote statistically significant differences (P < 0.05). Data expressed as means ± SE (n = 9 × 2). Initial average weight of fish is 32 ± 0.0 g.

Fig. 3

Serum superoxide dismutase (SOD) activity in rainbow trout fed diet containing fish oil (FO), soybean oil (SO), black soldier fly oil (BSLO), or BSLO + bile acid (BA) for 10 weeks. Different lower case letters between different dietary groups denote statistically significant differences (P < 0.05). Data expressed as means ± SE (n = 9). Initial average weight of fish is 32 ± 0.0 g.

Fig. 4

Catalase (CAT) and glutathione peroxidase (GPx) enzyme activities in the serum of rainbow trout fed diets containing fish oil (FO), soybean oil (SO), black soldier fly oil (BSLO), or BSLO + BA (BSLO + bile acid) for 10 weeks. Different lower case letters between different dietary groups denote statistically significant differences (P < 0.05). Data expressed as means ± SE (n = 9). Initial average weight of fish is 32 ± 0.0 g.

Fig. 5

Serum glucose concentration of rainbow trout fed diets containing fish oil (FO), soybean oil (SO), black soldier fly oil (BSLO), or BSLO + bile acid (BA) for 10 weeks. Different lower case letters between different dietary groups denote statistically significant differences (P < 0.05). Data expressed as means values ± SE (n = 9). Initial average weight of fish is 32 ± 0.0 g.