An optimal EPA/ARA ratio strategy for promoting ovarian development, reproductive performance, and larval stress resistance in Redclaw crayfish (Cherax quadricarinatus) female broodstock

Eicosapentaenoic acid (EPA) and Arachidonic acid (ARA) are essential for gonadal development, while their optimal ratio remains unclear due to their functionally distinct and potentially opposing roles. This study investigated the effects of different dietary EPA/ARA ratios (0.53, 1.12, 1.54, 2.09, and 2.50) on physiological metabolism, ovarian development, reproductive performance, and larval stress resistance in Cherax quadricarinatus (50.72 ± 0.40 g). The experimental period included nutritional enhancement (6 weeks), mating, spawning, and larval hatching (8 weeks), and an acute ammonia nitrogen stress test (96 h). The initial group comprised crayfish sampled post-acclimatization and prior to nutritional enhancement. Results revealed that the gonadosomatic index was significantly increased in all treatment groups compared with the initial group (P < 0.05). Compared to the control (0.53), dietary EPA supplementation significantly enhanced lipid metabolism in the hepatopancreas and promoted lipid transport to the ovary via the hemolymph (P < 0.05). The contents of progesterone and 17β-estradiol in serum were highest in the 2.09 group, notably exceeding those in the control (0.53) (P < 0.05). Moreover, crayfish in the 2.09 group exhibited upregulated expression of citrate cycle-related genes in the hepatopancreas and elevated contents of related metabolites in the ovaries, indicating enhanced energy anabolism (P < 0.05). N-glycan metabolism pathways in the hepatopancreas were significantly enriched in the 2.09 group (P < 0.05), suggesting increased synthesis of exogenous vitellogenin. Additionally, crayfish in the 2.09 group enhanced non-specific immune responses against inflammatory stress by activating the CYP450 pathway and phenoloxidase system (P < 0.05). In summary, a dietary EPA/ARA ratio of 2.09 enhances lipid metabolism, stimulates sex hormone and vitellogenin synthesis, and mitigates inflammatory responses, thereby supporting healthy ovarian maturation and improving reproductive capacity in C. quadricarinatus. Regression analysis estimated the optimal dietary EPA/ARA ratio for promoting ovarian development and reproduction in C. quadricarinatus female broodstock to be between 1.60 and 2.21.