Black soldier fly larval meal with exogenous protease in diets for rainbow trout (Oncorhynchus mykiss) production meeting consumer quality

Abstract

A protein gap exists within the supply of fish feed ingredients due to intensifying global aquaculture production and demands. This is distinctly acute in salmonid farming where protein requirements are higher to other aquatic farmed species. In pursuit of a viable alternative, an eight-week feeding trial was conducted to evaluate the feasibility of including reared black soldier fly (BSF, Hermetia illucens) larvae into rainbow trout (Oncorhynchus mykiss) diets. Five diets were formulated: a fish meal-based basal diet (CTRL), two diets of BSF incorporation at 15 and 30% (BSF15; BSF30), and two diets at the same incorporation level with the addition of a supplementary protease enzyme (BSF15P; BSF30P) assigned to test potential dietary enhancement. No significant growth performance between the dietary treatments was observed. The fish condition factor in BSF30 was higher than BSF30P (P=0.025). Fillets showed increased muscle yellowness as dietary BSF increased (P=0.004). Trout fed BSF displayed significantly lower lipid peroxidation post-harvest (P < 0.001), with the level of malondialdehyde decreasing with increased dietary BSF, regardless of protease inclusion. BSF meal elevated the saturated fatty acid content of fillets significantly (P < 0.001) while monounsaturated fatty acids decreased (P < 0.001). BSF protease treatments elevated the total concentration of protein in the trout body content, reflecting potentially improved protein utilisation efficiency. BSF diet with protease inclusion is a feasible protein and energy concentrate to replace fish meal in rainbow trout diets up to 30%, without negative effects on the growth, proximate composition, fatty acid profile, lipid peroxidation and fillet colour stability of rainbow trout.

Keywords

• Black soldier fly
• Rainbow trout
• Fish meal replacement
• Exogenous enzymes
• Protease
• Fillet quality