Insect Larvae Meal as a Complementary Functional Ingredient in High Soybean Meal‐Based Diets Improve the Health of Rainbow Trout ( Oncorhynchus mykiss )

Abstract

This study explores the integration of black soldier fly larvae (BSFL) as a complementary functional ingredient to increase the soybean meal (SBM) inclusion in rainbow trout ( Oncorhynchus mykiss ) diets. Six experimental diets were formulated including a control diet as fishmeal (FM), an SBM‐based diet, and 2.5% and 5% whole‐body (WB) or defatted (DB) BSFL‐supplemented SBM‐based diets. Results revealed that BSFL inclusion positively influences gut health, immune response and survival rates following challenge with Flavobacterium psychrophilum . Dietary lauric acid content significantly impacted whole‐body lauric acid levels in a dose‐dependent manner, with BSFL diets showing higher levels than FM and SBM diets. Fish fed diets with BSFL exhibited enhanced survivability against F. psychrophilum infection compared to SBM‐fed fish, with the highest survival rates observed in the WB5 (5% whole‐body BSFL) group. Histological analysis demonstrated improved intestinal morphology in BSFL‐fed fish, particularly evident in the absence of pathogenic enteritis. Gene expression analysis revealed upregulated proinflammatory markers (IL‐8, TNF‐α, C5) in BSFL‐fed fish post‐challenge, indicating an enhanced immune response. These findings indicate the potential of BSFL as a functional feed ingredient to complement high SBM inclusion in rainbow trout with improved health and performance. By strategically reducing inclusion levels and repositioning BSFL as a functional feed ingredient instead of fishmeal replacer in aquafeed formulations, one can mitigate economic concerns while maximising the benefits of this sustainable alternative.

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