Nutritional regulation by vitamin A: Comprehensive impacts on growth, molting, immunity, lipid metabolism, and ovarian maturation in red swamp crayfish (Procambarus clarkii).

This study focuses on the effects of dietary vitamin A on growth performance, immunity, molting, lipid metabolism, and ovarian development of red swamp crayfish (Procambarus clarkii). Six experimental diets with vitamin A levels of 0 IU/kg (A0), 3000 IU/kg (A1), 9000 IU/kg (A2), 27000 IU/kg (A3), 81000 IU/kg (A4), and 243000 IU/kg (A5) were feed to P. clarkii (initial weight: 8.74 ± 0.05 g) for 8 weeks. The results showed that adding 27000 IU/kg of vitamin A to the feed can increase the weight gain rate (WGR) and specific growth rate of P. clarkii, reduce the feed conversion ratio (FCR), and hepatosomatic index (P < 0.05). It can enhance the digestive capacity of the hepatopancreas and intestine of P. clarkii. Supplementation with 27000 IU/kg of vitamin A activated the MIH regulatory mechanism and mTOR signaling pathway by upregulating the mRNA expression of EcR, RXR, mTOR, S6K1, E75 and Chitinase (P < 0.05), and downregulating the mRNA expression levels of MIH and 4EBP1 (P < 0.05). Compared with the A0 group, the addition of 27000 IU/kg vitamin A significantly enhanced the immunity and antioxidant capacity of P. clarkii. Dietary vitamin A (27000 IU/kg) downregulated the mRNA levels of myd88, NF-κB p105, mapk7 and tnf in the intestine (P < 0.05), and upregulated the mRNA expression of tgf-β (P < 0.05), thereby activating the MAPK/NF-κB signaling pathway in P. clarkii. In terms of lipid metabolism, the addition of 27000 IU/kg vitamin A reduced the lipid content, upregulated the mRNA expression of genes related to lipid synthesis (fas, srebp1, acsbg, acc2) and lipid transport (fabp, fatp) (P < 0.05), and downregulated the mRNA levels of genes related to lipid decomposition (cpt-1, atgl, aco, pla2) (P < 0.05). The accumulation of lipid in the hepatopancreas was decreased in the A3 group. In terms of ovarian development, 27000 IU/kg of vitamin A promoted the development of ovaries by upregulating the mRNA expression of Vg, PKA, CyclinB, cdc2 and fox L2 (P < 0.05), and activating the ECR/RXR signaling pathway to promote the production of yolk. In conclusion, based on the evaluation indicators of WGR and FCR, adding 14491.48-15990.83 IU/kg of vitamin A to the feed of P. clarkii for the growth and physiological needs was recommended.