Effects of dietary histidine on growth, non-specific immune and ovarian development of the red swamp crayfish ( Procambarus clarkii )

To explore the effects of dietary histidine on growth, non-specific immune and ovarian development of red swamp crayfish ( Procambarus clarkii ), crayfish (5.98 +/- 0.11 g) were fed six isoproteic and isoenergetic diets with histidine levels (3.90 (control), 5.67, 8.42, 10.57, 12.32, and 15.02 g/kg) for eight weeks. The results showed that nearly all tested indicators demonstrated significant linear or quadratic trends with the variation of histidine levels. Weight gain rate (WGR), feed conversion ratio (FCR), protein efficiency rate (PER), protein deposition rate (PDR), and essential amino acid deposition rates obtained the optimal values when the dietary histidine level was 8.42 g/kg or 10.57 g/kg. Compared to the control group, the 8.42 g/kg group exhibited enhanced nonspecific immunity and antioxidant properties, and the 10.57 g/kg group demonstrated significant increase in the frequency of B cells in the hepatopancreas, the length and width of intestinal villi and the activities of protease and lipase. Additionally, the 10.57 g/kg group showed elevated ecdysterone hormone, gonadal index (GI), cAMP content and the relative abundance of beneficial intestinal microbiota. The mRNA expressions of MIH , ECR , RXR , chitinase , PKA , fox L2 , Vg , cdc2 , and cyclin B genes were also significantly modulated by dietary histidine levels. Overall, dietary histidine improved the intestinal health and regulated the immune function to enhance protein utilization and promote growth performance of red swamp crayfish. In addition, dietary histidine improved the synthesis of yolk substance, promoted the development of ovarian cells, and then improved the ovarian index of female crayfish. Based on the quadratic curve regression model analysis of the relationship between WGR, SGR, PDR, PER, FCR, GI and dietary histidine level, the optimal histidine level was 9.36 - 10.91 g/kg (dry matter), corresponding to 26.63 - 31.04 g/kg of dietary protein in red swamp crayfish.