Aquaculture is the fastest-growing sector of agriculture and supplies over half of global fish consumption. Alternative aquafeed options have been explored to improve efficiency and lower production and environmental costs. Soybean meal (SBM) is a major ingredient in the aquafeed industry, and the high inclusion of SBM exhibits soybean-induced enteritis in carnivore fish, including Atlantic salmon (Salmo salar). The black soldier fly (Hermetia illucens) is an efficient, nutritionally sound ingredient. Using black soldier fly meal as a complementary ingredient in SBM-based diets has been shown to improve the performance of rainbow trout in terms of growth performance and mitigate enteritis. Therefore, our goal was to evaluate the effects of whole black soldier fly larval meal (WBLM) as a complementary feed ingredient in soybean meal-based diets on gut health, and regulation of inflammatory, ionregulatory homeostasis, and oxidative stress associated genes in Atlantic salmon.
Seven isonitrogenous (42% crude protein) and isolipidic (20% lipid) experimental diets: fish meal-based diets (FM), low-level SBM-based diets (LS), SBM+5% and 10% WBLM (LS-WB5 and LS-WB10), and high-level SBM-based diets (HS), SBM+5% and 10% WBLM (HS-WB5 and HS-WB10). A total of 630 Atlantic salmon (15 g) were distributed in 21 tanks (triplicates) in a recirculatory aquaculture system and sampled at three time points (days 28, 56, and 84). All the data were subjected to one-way ANOVA using R programming.
At the end of an 84-day feeding trial, the results revealed that feeding dietary SBM at a low (30%) or higher (40%) level did not affect the growth parameters of Atlantic salmon (p > 0.05). The histology of the distal intestine showed that there were no differences in the lamina propria thickness (P = 0.630), connective tissue thickness beneath the folds (P = 0.309), or overall fold size or thickness (P = 0.356) among the dietary groups. Gene expression within the liver revealed no differences between diets fed in immune response (il8, nf-kb, and tnfa: p > 0.05), or ionregulatory homeostasis (claudins 25b and occludin: p > 0.05). Similarly, no difference was observed in oxidative-stress-related gene expression within the liver (gpx1a, gsr, cat, and sod1: p = 0.845). Gut microbiome data are being analyzed and will be presented.
Conclusively, the current study has shown that Atlantic salmon could utilize a high level of soybean meal with no detrimental effects on growth, and the addition of whole black soldier larvae meal (WBLM) did help mitigate SBM-induced enteritis, inflammatory response in groups fed a high (40%) SBM diet. Thus, formulating practical diets with FM and high SBM is possible for sustainable Atlantic salmon aquaculture.