Defatted black soldier fly (Hermetia illucens) diets improved hemato-immunological responses, biochemical parameters, and antioxidant activities in Streptococcus iniae-infected Nile tilapia (Oreochromis niloticus).

Background: Challenges of limited supply and increasing prices of fishmeal have driven the aquaculture nutritionists to seek alternative sustainable protein rich ingredients to keep manufacturing aquafeeds in a maintainable and cost-effective way. Black soldier fly, Hermetia illucenslarvae meal represent great potential as a sustainable alternative to fishmeal in aquafeeds.

Methods: Three replacement diets for fishmeal were prepared at different levels of defatted black soldier fly (Hermetia illucens) meal (DBSFM): Diet 1 (0 g DBSFM /kg diet, control), 33% (DBSFM-33%, 66 g DBSFM /kg diet), and 100% (DBSFM-100%, 200 g DBSFM /kg diet) to investigate their effects on biochemical parameters, immuno-hematological responses, antioxidant activities, and inflammatory gene expression in Nile tilapia, Oreochromis niloticus, a total of 270 (40.0 ± 0.50 g) before and after challenge with Streptococcus iniae (S. iniae). The feeding trial lasted six weeks (pre-challenge) and two weeks (post-challenge).

Results: The results showed a significant improvement in white blood cell count (P < 0.01), lymphocyte count (P < 0.01), serum lysozyme activity (P < 0.001), and phagocytic activity (P < 0.001), mostly in the DBSFM-100% group following the pre-challenge phase compared to the control group. Post-challenge phase exhibited significant increases in blood indices in the DBSFM-treated groups compared to the control group. Following pre- and post-challenge periods, both DBSFM-supplemented groups experienced significant increases (P < 0.01, P < 0.001), in serum total protein levels. Albumin and globulin levels also experienced similar increases (P < 0.05, P < 0.01), but only post-challenge. Total antioxidant capacity exhibited a significant increase in both DBSFM-supplemented groups following the post-challenge, as did superoxide dismutase, catalase, and glutathione peroxidase in the liver and spleen. Conversely, levels of glucose, cortisol, and malondialdehyde followed the opposite trend. DBSFM-100% inclusion revealed significant (P < 0.05) up-regulation of interleukin 1β (IL-1β) in the pre-challenge phase compared to control, but no significance (P > 0.05) was seen for other genes. Anti-inflammatory-related genes transforming growth factor-β and interleukin-10 mRNA expression levels were up-regulated in DBSFM-supplemented groups compared to the control post-challenge, but the opposite was seen for IL-1β and tumor necrosis factor- α.

Conclusion: These findings suggest that Nile tilapia challenged with S. iniae may experience significant enhancements in hemato-immunological parameters, antioxidant capability, and anti-inflammatory gene expression when fish meal is replaced with DBSFM up to 100%.