Atlantic salmon (Salmo salar) aquaculture continues to grow, and research into alternative feed ingredients is crucial for its sustainable production. This study aimed to evaluate the substitution of fishmeal (FM) with defatted black soldier fly larvae (DBSFL) and soy protein meals (SOY) in the diet of Atlantic salmon using growth performance, health parameters, and nutrigenomics approaches.
A 12-week feeding trial was conducted in a recirculating aquaculture system at UMaine - ARI. Thirty Atlantic salmon parr (36.4 ± 0.1g, initial weight) were randomly stocked into triplicate tanks (300 L each). A control diet (100%FM) and six test diets (factorial design) containing three levels of DBSFL (10%, 15% and 20% of the diet) and two levels of SOY (12% and 19% of the diet) were evaluated.
All dietary treatments had high survival (greater or equal to 99%). Dietary DBSFL significantly affected fish growth, with a high final weight (141.84 ± 2.67g) and weight gain (291.25 ± 6.45%) in fish fed 10%DBSFL+12%SOY diet compared to those fed 20%DBSFL+12%SOY (116.61 ± 7.43g and 221.53 ± 21.35%, respectively), but similar with the other treatments. Two-way interactive effects were found on 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%DBSFL+12%SOY diet. The 20%DBSFL+12%SOY and 10%DBSFL+19%SOY diets significantly improved plasma TIBC in contrast to 20%DBSFL+19%SOY. Plasma cortisol and alkaline phosphatase levels were significantly elevated in fish fed the 20%DBSFL+19%SOY diet compared to those fed the control and 15%DBSFL+19%SOY diets. DBSFL 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 genes expression were upregulated in fish fed the 15%DBSFL+12%SOY diet compared to those fed the 20%DBSFL+19%SOY. IgM and IgT expressions were significantly increased in fish fed the 15%DBSFL+12%SOY diet in contrast to those fed high-SOY diets, except 10%DBSFL+19%SOY. The 20%DBSFL+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 DBSFL meal (up to 15% of the diet) could replace fishmeal without compromising Atlantic salmon growth and health; and alleviate inflammation caused by anti-nutritional factors derived from soy protein.