Effects of dietary n-3 HUFA levels achieved by fish oil adjustment on antioxidant capacity, lipid metabolism, intestinal health and testes development of male Macrobrachium rosenbergii

This study investigated the effects of dietary n-3 highly unsaturated fatty acids (n-3 HUFA) on growth performance, antioxidant capacity, lipid metabolism, intestinal morphology, and testes development in male Macrobrachium rosenbergii , aiming to determine the optimal dietary inclusion level of n-3 HUFA. Prawns with an initial weight of 17.49 ± 0.14 g were fed six isonitrogenous and isolipidic diets containing graded levels of n-3 HUFA: 0.12% (CON), 0.31% (T1), 0.60% (T2), 0.83% (T3), 1.10% (T4), and 1.31% (T5). The T2 group showed the best growth performance, with significantly higher final body length (FBL) and specific growth rate (SGR) ( P <0.05). Broken-line regression analysis indicated that 0.57% n-3 HUFA is optimal for maximizing weight gain. The antioxidant enzyme results showed that the T2 group exhibited higher activities of total superoxide dismutase (T-SOD), total antioxidant capacity (T-AOC), and catalase (CAT), together with the lowest malondialdehyde (MDA) content, indicating the strongest antioxidant capacity in this group. Increasing dietary n-3 HUFA levels resulted in reduced triglyceride (TG) and elevated high-density lipoprotein cholesterol (HDL) contents, with T5 showing the most improved lipid profile. Histological analysis revealed more intact hepatopancreatic structure in the T1 and T2 groups, and superior intestinal fold height and width in T2, while the T2 and T3 groups showed better testes development. Analysis of the intestinal microbiota based on 16S rRNA gene sequencing revealed that the T2 group exhibited higher intestinal α-diversity, with ASVs, ACE, and Chao1 indices all being significantly higher than those in the other groups ( P <0.05). Concurrently, the relative abundance of potentially pathogenic bacterial families, namely Enterobacteriaceae and Mycoplasmataceae , demonstrated a decreasing trend with increasing dietary n-3 HUFA levels. These results suggest that dietary n-3 HUFA at 0.57–0.83% enhances growth, testes development, antioxidant status, lipid metabolism, and intestinal health in male M. rosenbergii . • The optimal dietary n-3 highly unsaturated fatty acid (n-3 HUFA) level for male Macrobrachium rosenbergii was determined to be 0.57%–0.83% of the diet. • Moderate dietary n-3 HUFA supplementation improved growth performance, antioxidant capacity, lipid metabolic homeostasis, and testes development. • Excessive dietary n-3 HUFA increased the metabolic burden in male prawns.