The Influence of Eicosapentaenoic Acid on Macrobrachium rosenbergii Broodstock: Ovarian Development, Antioxidant Status, and Lipid Metabolism.

Lipids are essential for crustacean reproduction, supporting broodstock growth and ovarian development. However, studies of n-3 highly unsaturated fatty acids (HUFAs), particularly eicosapentaenoic acid (EPA), on the growth and ovarian development of prawn broodstock remain limited. Accordingly, five experimental diets containing EPA concentrations of 0.12%, 0.79%, 1.46%, 2.21%, and 2.78% were formulated to examine their effects on ovarian development and broodstock health in the giant freshwater prawn Macrobrachium rosenbergii (initial weight: 9.32 ± 0.52 g) and to determine dietary EPA requirements during ovarian maturation. The results were as follows: (1) no significant differences in survival rate were observed among groups. Weight gain (WG) initially increased and then declined, reaching the highest values in the 1.46% EPA group, although differences among treatments were not significant. In contrast, hepatopancreas index decreased significantly with increasing dietary EPA (p < 0.05). (2) Dietary EPA significantly altered hepatopancreatic fatty acid composition. Saturated fatty acid (SFA) levels showed no significant differences, whereas monounsaturated fatty acids (MUFAs) decreased significantly (p < 0.05). In contrast, polyunsaturated fatty acids (PUFAs) and HUFA increased significantly with higher dietary EPA (p < 0.05), peaking in the 2.78% EPA group. (3) Antioxidant parameters, including total antioxidant capacity (T-AOC), total superoxide dismutase (T-SOD), and glutathione peroxidase (GSH-Px), followed a pattern of initial increase followed by decline with higher EPA levels (p < 0.05). Malondialdehyde (MDA) content showed the opposite trend, reaching its lowest level in the 1.46% EPA group (p < 0.05). (4) Ovarian histology revealed that the 1.46% EPA group exhibited a higher proportion of mature oocytes, with most females reaching ovarian development stages III-IV, and this group also showed the highest gonadosomatic index (GSI). Steroid hormone secretion was significantly affected by dietary EPA (p < 0.05). (5) At the molecular level, EPA inhibited the expression of genes related to lipid synthesis in the hepatopancreas (p < 0.05) and promoted fatty acid β-oxidation, but excessive EPA caused irreversible hepatopancreatic damage. Polynomial regression analysis of steroid hormone secretion indicated that 1.32% and 1.50% dietary EPA supported maximum progesterone (PROG) and 17β-estradiol (E2) levels, respectively. Overall, a dietary EPA level of 1.46% was found to promote broodstock growth, enhance antioxidant capacity, accelerate fatty acid β-oxidation, stimulate steroid hormone secretion, and provide sufficient energy for ovarian development in the giant freshwater prawn.