Gamma ray irradiation enhances defatted Hermetia illucens larvae meal as a dietary alternative to fishmeal for Acanthopagrus schlegelii juveniles

The current research investigated whether gamma (gamma)-irradiation could improve the viability of defatted Hermetia illucens larvae (HIL) meal as a fishmeal alternative in black sea bream (Acanthopagrus schlegelii) diets. Three diets were formulated with equal protein (420 g/kg) and lipid (80 g/kg) contents. A diet containing 400 g/kg fishmeal was served as the control diet (C), and 50% of fishmeal in diet C was replaced by either defatted HIL meal or gamma-irradiated defatted HIL meal to produce diet HR and diet HR10, respectively. Fish fed diet HR exhibited lower final body weight and weight gain compared to those fed diet C, while no statistically significant differences were found between fish fed diets C and HR10. Additionally, fish fed diet HR10 exhibited significantly lower feed intake, feed conversion rate, nitrogen waste, hepatic malondialdehyde content, relative usage of fishmeal and fish oil, fish -in to fish -out ratio, and economic conversion ratio, and meanwhile significantly higher nitrogen retention efficiency, hepatic total antioxidant capacity, economic profitability index and profitability, than those fed diet C. Fish fed different test diets showed statistically equal alpha diversity of intestinal microbiota, whereas the beta diversity of intestinal microbiota in group HR was far from groups C and HR10. Compared to fish fed diet C, the gut microbiota composition of fish fed diet HR showed significant alterations at both the phylum and genus levels. However, the altered composition of intestinal bacteria was partially restored in fish fed diet HR10. The above findings indicate that treating defatted HIL meal with gamma-ray can reduce dietary fishmeal content for black sea bream to 200 g/kg without any adverse effects on growth, proximate composition and intestinal microbial diversity, and meanwhile ameliorates the feed utilization, hepatic antioxidant capacity, and intestinal microbiological composition of black sea bream. Furthermore, feeding gamma-irradiated defatted HIL meal enhances the economic profitability, while reduces the waste output and reliance on fishery resource of black sea bream aquaculture.