Effects of fishmeal substitution with defatted black soldier fly larvae and soy protein meals on the growth, physio-biochemical responses, and immune-related gene expression of Atlantic salmon (Salmo salar)

A 12-week growth trial was conducted to evaluate the substitution of fishmeal (FM) with defatted black soldier fly larvae (BSFL) and soy protein (SOY) meals in the diet of Atlantic salmon ( Salmo salar ) using growth performance, health parameters, and nutrigenomic approaches. Thirty Atlantic salmon parr (36.4 ± 0.1 g, initial weight) were randomly stocked into each of 21 tanks. A control diet (100 %FM) and six test diets (factorial design) containing three levels of defatted BSFL (10 %, 15 %, and 20 % BSFL of the diet) and two levels of soy protein (12 % and 19 % SOY of the diet) were evaluated using a completely randomized design in triplicates for 12-weeks. The results indicated that dietary BSFL significantly affected fish growth, with a high final weight (141.84 ± 2.67 g) and weight gain (291.25 ± 6.45 %) in fish fed 10 %BSFL+12 %SOY diet compared to those fed 20 %BSFL+12 %SOY (116.61 ± 7.43 g and 221.53 ± 21.35 %, respectively), but not significantly different compared to the control and other treatments. Two-way interactive effects were found on the hepatosomatic index, plasma alanine aminotransferase, immunoglobulin M, total iron-binding capacity (TIBC), cortisol, and head-kidney insulin-like growth factor-I ( P = 0.005, 0.043, 0.009, 0.006, 0.004 and 0.022, respectively). The highest plasma IgM level was measured in the group fed 15 %BSFL+12 %SOY diet. The 20 %BSFL+12 %SOY and 10 %BSFL+19 %SOY diets significantly improved plasma TIBC in contrast to 20 %BSFL+19 %SOY. Plasma cortisol and alkaline phosphatase levels were significantly elevated in fish fed the 20 %BSFL+19 %SOY diet compared to those fed the control diet. BSFL meal significantly altered the relative expressions of immune-related genes (IgD and IFN-γ), while SOY influenced the growth (IGF I) and immune-related (IgM, IgD, IgT, IFN-γ, and IL-1β) genes in the head-kidney of Atlantic salmon. IGF-I and IgD gene expression were upregulated in fish fed the 15 %BSFL+12 %SOY diet compared to those fed the 20 %BSFL+19 %SOY. IgM and IgT expressions were significantly increased in fish fed the 15 %BSFL+12 %SOY diet in contrast to those fed high-SOY diets, except 10 %BSFL+19 %SOY. The 20 %BSFL+19 %SOY diet significantly elevated head-kidney pro-inflammatory cytokine gene (IFN-γ) expression compared to the low-SOY diets. The overall results suggest that defatted BSFL meal, up to 15 % of the diet, replaced fishmeal without compromising Atlantic salmon growth and health; and alleviated inflammation caused by anti-nutritional factors derived from soy proteins. • 10 % defatted black soldier fly larvae (BSFL) and 12 % soy proteins (SOY) increased Atlantic salmon growth. • 15 %BSFL +12 %SOY diet improved Atlantic salmon immune capacity (including plasma IgM and head-kidney IgM, IgD, and IgT genes). • High-SOY diet elevates the head-kidney pro-inflammatory cytokines of Atlantic salmon. • Defatted BSFL, up to 15 % of the diet, replaces fishmeal without compromising Atlantic salmon growth and health. • Defatted BSFL and SOY can be strategically used to improve farmed Atlantic salmon's immune function (health).