Effects of enzymatic hydrolysate of black soldier fly (Hermetia illucens) in low protein diets for common carp (Cyprinus carpio): Promoting growth, enhancing antioxidant and immunity

This study investigated the effects of an enzymatic hydrolysate of black soldier fly (EHBSF, Hermetia illucens ), produced using a compound enzyme technique, in low protein diets over an 8-week feeding trial. A total of 270 juvenile common carp ( Cyprinus carpio ) were assigned to 6 groups consisting of one 34 % crude protein diet and five 32 % crude protein diets supplemented with 0, 10, 15, and 20 g/kg EHBSF, along with a group receiving 15 g/kg commercially available zymolytic BSF paste (named as CP, LP, LE10, LE15, LE20, and LC15). Dietary EHBSF enhanced growth and feed utilization in all LE and LC15 groups compared to the LP group. The crude protein content increased in LE groups, while the hepatopancreas crude lipid content decreased in the LE20 group. SOD contents in the hepatopancreas, spleen, and intestine of LE15 group were up-regulated. The T-AOC contents in the serum, hepatopancreas, and spleen of LE15 and LE20 groups were higher. The MDA contents in the spleen and kidney of LE and LC15 group were down-regulated. LE and LC15 groups mitigated structural damage to the hepatopancreas and kidney of fish caused by LP diets and promoted intestinal development. 15 g/kg EHBSF in LP diets up-regulated the expression of antioxidant genes in hepatopancreas, spleen, and kidney. Furthermore, at least 15 g/kg EHBSF in LP diets down-regulated the expression of pro-inflammatory genes and up-regulated the expression of anti-inflammatory genes. Overall, the incorporation of EHBSF into LP diets significantly enhanced growth, promoted tissues (hepatopancreas, kidney, and intestine) health, and improved antioxidant and immune responses of common carp. The effects of the appropriate dose of EHBSF on the growth and health of carp were similar to commercially available zymolytic BSF paste. Furthermore, regression analysis of SGR and PER determined the optimal dosage of EHBSF in LP diets for common carp to be between 20 and 21.70 g/kg. • Enzymatic hydrolysate of black soldier fly (EHBSF) in low protein (LP) diets enhanced the growth of common carp ( Cyprinus carpio ). • EHBSF in LP diets promoted the health development of tissues structure of common carp. • EHBSF in LP diets improved antioxidant and immune responses of common carp. • Based on the regression analysis of SGR and PER, the optimal dosage of EHBSF in LP diets for common carp ranged from 20 to 21.70 g/kg.