Dietary arginine modulates growth performance and testicular development across life stages in male swimming crab (Portunus trituberculatus).

This study evaluated the effects of dietary arginine (Arg) on growth performance, testicular development, and apoptosis in juvenile and adult male swimming crabs (Portunus trituberculatus). Six isonitrogenous and isolipidic diets were formulated with graded Arg levels of 1.89% (control), 2.27%, 2.65%, 3.05%, 3.43%, and 3.80%, respectively. A total of 180 juvenile male crabs (initial weight: 4.35 ± 0.02 g) were randomly assigned to six treatments (three replicates of 10 crabs each) and cultured for 20 weeks. Four crabs per replicate were sampled at week 13 (juvenile stage), and the remaining six crabs per replicate were sampled at week 20 (adult stage). At the juvenile stage, compared with the control, those fed the 2.27% Arg diet exhibited significantly higher final body weight (FBW), percent weight gain (PWG), specific growth rate (SGR), and feed efficiency (FE) (P < 0.05). Conversely, the lowest growth performance was observed in the 3.80% Arg group, whereas feed intake (FI) showed an inverse trend (P < 0.001). In the hemolymph, crabs fed the 2.27% Arg diet exhibited the highest activities of endothelial nitric oxide synthase (e-NOS), superoxide dismutase (T-SOD), catalase (CAT), as well as the highest total antioxidant capacity (T-AOC), and glutathione (GSH) content, which were significantly higher than those in the control (P < 0.05). In the hepatopancreas, the relative expression of immune-related genes (mnsod, gsh-px, relish, and po) were upregulated in the 2.27% Arg group compared with control (P < 0.05). And the relative expression of genes involved in lipid synthesis (fas, dgat, acc, and fad) and lipid catabolism (cpt-1, fatp, and fabp) were significantly elevated (P < 0.05), and B-cell diameter was significantly reduced in 2.27% Arg group compared with the control (P < 0.001). At the adult stage, crabs fed 2.27% and 2.65% Arg diets showed higher gonadosomatic index, testis index and vas deferens index than those fed other diets (P < 0.05). In the hemolymph, the activities of adenylate kinase (AK) and neuronal nitric oxide synthase (n-NOS), as well as nitric oxide (NO) content, were significantly increased in the 2.65% Arg group (P < 0.05), while hemolymph ammonia content was significantly decreased compared with the control (P = 0.007). Compared with the control, testicular relative expression of genes involved in Arg metabolism (odc1, creatinase, nadh6, sms, and nnos), spermatogenesis (iag, dsx, and soxe), and protein synthesis (tor) were significantly elevated in the 2.65% Arg group (P < 0.05). Furthermore, compared with the control, 2.65% Arg enhanced anti-apoptotic gene (bcl2) relative expression, reduced BAX/BCL-2 and P-JNK/JNK ratios, decreased apoptotic cell proportion, and lowered reactive oxygen species (ROS) mean fluorescence levels in the testis (P < 0.05). In conclusion, the optimal dietary Arg requirements for juvenile and adult P. trituberculatus were estimated to be 2.04% and 2.46%, respectively. Furthermore, dietary supplementation with 2.27% Arg maximally enhanced growth and immune function in juvenile crabs, whereas 2.65% Arg could improve Arg metabolism, promote testicular development, and reduce cell apoptosis in adult male crabs.