Black Soldier Fly, Hermetia illucens as an Alternative to Fishmeal Protein and Fish Oil: Impact on Growth, Immune Response, Mucosal Barrier Status, and Flesh Quality of Juvenile Barramundi, Lates calcarifer (Bloch, 1790)

SIMPLE SUMMARY: Fishmeal and fish oil being recognized as nutritionally balanced and preferred protein and lipid sources in aquafeeds for finfish farming. However, the limited supply, soaring prices, and depletion of wild capture fisheries have prompted the aquaculture industry to look for widely available and less expensive alternatives for fishmeal and fish oil to ensure the sustainability of aquaculture production. As an alternative to fishmeal protein and oil, black soldier fly (BSF) larvae is considered a promising candidate for its high protein, lipid and minerals content, as well as for its bioactive potential with anti-microbial, anti-fungal, and anti-viral functions. This study investigated the effects of partial substitution of fishmeal protein and fish oil with partially defatted BSF larvae protein and oil on growth performance, non-specific immunity, mucosal barrier status and muscle fatty acids composition in barramundi. The findings of the study confirmed that BSF could substitute 30% fishmeal and fish oil successfully without compromising the growth of barramundi. Further, partial replacement of fishmeal and fish oil with BSF diets improved bactericidal activity, immune-related cytokine expression, and mucin cells in both gut and skin which are an indication of improved immunity of barramundi. ABSTRACT: A feeding trial was conducted to test the effects of partial replacement of fishmeal (FM) protein and fish oil (FO) with partially defatted black soldier fly, Hermetia illucens insect protein, and oil, respectively, on growth performance, immune response, gut and skin barrier status, and flesh quality in juvenile barramundi. Four isonitrogenous and isocaloric diets used in the study were a control diet based on FM, 30% FM replaced with H. illucens protein (HiP), 30% FO replaced with H. illucens oil (HiO), and both 30% FM and 30% FO replaced with H. illucens protein and oil (HiPO). Diets were fed twice a day to satiety in triplicated groups of barramundi with an initial body weight of 1.74 ± 0.15 g per fish. At the end of the trial, growth and feed utilization indices were found insignificant (p > 0.05) between the test diets and control. A significant increase in bactericidal activity was observed in fish fed the HiP diet while serum lysozyme activity was unchanged. Stress-related heat shock proteins (HSP70 and HSP90) did not differ significantly among the test diets while immune-relevant genes (IL-1β and IL-10) were significantly upregulated in HiP and HiOP groups. The number of mucin cells were increased in the gut and skin of HiP and HiOP fed fish when compared to the control diet. The total fatty acid compositions (∑SFA, ∑MUFA, ∑PUFA, ∑n-3, and ∑n-6) in the muscles of barramundi were not significantly influenced with H. illucens protein and oil diets when compared to the control.