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%.