Effects of arginine supplementation in plant-protein-based low-fishmeal feed on growth, feeding, antioxidant, immune and intestinal structure of Macrobrachium nipponense

Arginine (Arg) plays a vital role in the regulation of body growth, antioxidant defense, and protein synthesis. The study aimed to evaluate the effects of plant-protein-based low-fishmeal feed supplemented with arginine on feeding, antioxidant capacity, immunity and intestinal morphology in Macrobrachium nipponense. Five isonitrogenous and isoenergetic dietary groups were formulated to contain varying levels of dietary arginine (0%, 0.60%, 1.20%, 1.80% and 2.40%, respectively) under low fish meal content and high plant protein inclusion. The measured arginine concentrations in diets were: 0.80% (0.80% Arg), 1.33% (1.33% Arg), 1.85% (1.85% Arg), 2.24% (2.24% Arg) and 2.65% (2.65% Arg). The feeding trial lasted for 8 weeks. The results showed that weight gain initially increased with higher dietary arginine levels before declining; peak values were observed in the group receiving 1.85% Arg, which significantly surpassed those recorded for the groups receiving diets with 0.80%, 1.33%, or 2.65% Arg (P<0.05). Conversely, the feed conversion ratio (FCR) exhibited an inverse trend, reaching its lowest point in the group fed with a diet containing 1.85% Arg, this value was significantly lower than that of both the groups receiving diets with either 0.80% or 2.65% Arg (P<0.05). No significant differences were found regarding survival rate (SR) or feeding rate (FR) among all experimental groups (P<0.05). With the increase in arginine levels, the activity of glutathione peroxidase (GSH-Px) and the content of glutathione (GSH) in the 1.85% Arg group were higher than those observed in the 0.80% Arg group (P<0.05). Additionally, the activity of superoxide dismutase (SOD) in the 1.85% Arg group was also greater than that found in the 0.80%, 1.33%, and 2.65% Arg groups (P<0.05). The malondialdehyde (MDA) content in the 1.85% Arg group was notably lower than that of all other groups, reaching statistical significance (P<0.05). Furthermore, aspartate aminotransferase (AST) activity was lowest in the 1.85% Arg group and significantly lower compared to both the 0.80% and 1.33% Arg groups (P<0.05). The alanine aminotransferase (ALT) activity recorded for both the 1.33% and 1.85% Arg groups was also at its lowest level, significantly less than that seen in the 0.80%, 2.24%, and 2.65% groups (P<0.05). The target of rapamycin (tor) and neuropeptide Y (npy) mRNA expression level in hepatopancreas was upregulated in 1.33% Arg group, and higher than that in the other four groups (P<0.05). The ribosomal proteins 6kinase (s6k) mRNA expression level in 1.85% Arg group was the highest and significantly higher than that in 2.24% Arg and 2.65% Arg groups (P<0.05). The leptin mRNA expression level decreased firstly and then increased, and its expression level was the highest in 0.80% Arg group. The intestinal microvilli in both the 1.85% and 2.24% Arg groups appeared intact, closely arranged, numerous, and slender. It was shown that Arg at a level of 1.85% in plant-protein-based low-fishmeal feed can enhance intestinal morphology, growth performance, antioxidant capacity, and the mRNA levels of genes related to tor signaling pathway and appetite regulation in M. nipponense. Based on second-order regression analysis of weight gain vs. dietary Arg level, the ideal dietary Arg levels for M. nipponense was 1.83%.