Treatment of Dietary Defatted Hermetia illucens Larvae Meal With Different Doses of γ-Rays: Effects on Growth, Waste Production, Antioxidant Capacity, and Gut Microbiota in Acanthopagrus schlegelii.

The response of Acanthopagrus schlegelii to dietary defatted Hermetia illucens larvae (HIL) meal irradiated by γ-rays at various doses was examined. Five test diets containing 80 g/kg crude fat, 420 g/kg crude protein, and 200 g/kg fishmeal were designed. All test diets contained 224 g/kg defatted HIL meal irradiated with γ-rays at a dose of 0 (D0), 5 (D5), 10 (D10), 20 (D20), or 40 kGy (D40). Compared to fish fed diet D0, fish fed diets D5 and D10 exhibited higher values of final body weight, weight gain, retention efficiencies of carbon, nitrogen, and phosphorus, and hepatic total antioxidant capacity, but lower values of feed intake and feed conversion ratio. Opposite trend was observed for these parameters in fish fed diets D20 and D40. No significant differences were observed in the condition factor, hepatosomatic index, and body contents of moisture, crude protein and lipid, carbon, and phosphorus among different groups. Compared to fish fed diet D0, fish fed diets D5 and D10 exhibited reduced or statistically equivalent waste excretion of carbon, nitrogen, and phosphorus. Fish from groups D20 and D40 exhibited higher Simpson index than fish from group D0. The beta diversity of intestinal bacteria differed between fish fed diets D0, D5, and D10 and those fed diets D20 and D40. A gradual decrease in the populations of the pathogenic bacteria Ralstonia and Pseudomonas was observed with increasing irradiation intensity. In contrast, the population of the intestinal probiotic bacteria Achromobacter increased two to four times. The results demonstrate that the potential of γ-irradiated defatted HIL meal as a protein ingredient for Acanthopagrus schlegelii is irradiation dose dependent. Overall, γ-irradiation of dietary defatted HIL meal at 5 or 10 kGy is beneficial for Acanthopagrus schlegelii.