An 8-week feeding trial was conducted to investigate the effects of dietary protein levels on growth performance, feed utilization, and energy retention of juvenile dotted gizzard shad Konosirus punctatus based on the variation of fish meal. Fish meal was used as the sole protein source; five semi-purified diets were formulated with varying crude protein (CP) levels of 22.52%, 28.69%, 34.85%, 38.84%, 45.78% (CP1-CP5 diets). A total of 300 uniform juveniles with initial body weight 3.61 ± 0.20 g fish⁻¹ were randomly divided into five groups with three replicates in each group. The results showed that different CP levels did not significantly affect the survival of juvenile K. punctatus (p > 0.05). The values of weight gain (WG) and specific growth ratio (SGR) showed a general enhancing trend and then weakened with increasing dietary CP levels (p > 0.05). Feed utilization also improved with increasing dietary CP levels (p > 0.05), and the optimal feed conversion ratio (FCR) value was found in fish fed the diet with CP3 (p > 0.05). The rise of dietary CP from 22.52% to 45.78% enhanced the daily feed intake (DFI) and protein efficiency ratio (PER) values of K. punctatus (p < 0.05). With the increase of dietary CP levels, daily nitrogen intake (DNI), energy retention (ER), and lipid retention (LR) elevated, while retention (NR), daily energy intake (DEI), and daily lipid intake (DLI) reduced (p < 0.05). No statistical differences in the content of water, crude protein, and crude lipid were observed among different treatments (p > 0.05). The activity of lipase in CP3 and CP4 diets was significantly higher than that of the CP1 diet (p < 0.05). Fish fed CP2 and CP3 diets had significantly higher amylase activity than that of the CP5 diet (p < 0.05). The levels of alanine aminotransferase (GPT) first enhanced and then decreased as dietary CP levels raised. The second-order polynomial regression model analysis of the WG and FCR indicated that the optimal dietary protein level for K. punctatus is about 31.75–33.82% based on the variation of fish meal.

An 8-week feeding trial was conducted to assess the effects of different dietary lipid levels on the growth performance, feed utilization, and body composition of juvenile kelp grouper Epinephelus moara. Six diets with varying lipid levels of 2.82%, 5.30%, 7.83%, 11.76%, 14.19%, and 16.32% (designated as CL1 to CL6) were carefully formulated. A cohort of 324 juvenile fish (initial body weight of 5.87 ± 0.09 g fish⁻¹) were randomly divided into six groups with three replicates in each group. The results showed that weight gain (WG) significantly improved as the dietary lipid level increased to 7.83%, followed by a decline with further increases. Fish fed the diet with 7.83% lipids also exhibited the highest feed efficiency (FE) and protein efficiency ratio. Although daily nitrogen intake and daily energy intake varied, no significant differences in nitrogen retention and energy retention were detected among the groups. With the increase in dietary lipid levels, daily lipid intake and daily lipid gain significantly increased, but lipid retention showed a consistent decline. Additionally, the viscerosomatic index and intraperitoneal fat ratio and the lipid content of the whole body, dorsal muscle, and liver increased significantly with increasing dietary lipid levels. The hepatic glycogen content inversely decreased with the elevation in dietary lipid levels. The lowest total cholesterol content in the serum was detected in the 16.32% dietary lipid treatment. According to the second-order polynomial regression analysis of WG and FE, a dietary lipid level of 6.56–9.31% was optimal for the growth performance and feed efficiency of juvenile kelp grouper.

This study examines the impact of the arginine/lysine ratio in feed on the growth, serum amino acids, arginine metabolism, and antioxidant capacity of juvenile largemouth bass (5.95 ± 0.02 g). Five isonitrogenous and isolipidic diets with varying arginine/lysine ratios were formulated and administered over an eight-week period. The results indicated that the treatments had no significant effect on protein efficiency ratio (PER), daily feed intake (DFI), or morphological indices of juvenile largemouth bass (p > 0.05). When the arginine/lysine ratio was 0.85 (2.25/2.65; 2.54/3.00), liver antioxidant capacity was maximized, and inflammatory factors were suppressed. Conversely, a ratio of 2.25/2.99 significantly reduced weight gain (WG) and specific growth rate (SGR) in juvenile largemouth bass, inhibited arginase activity, and increased serum total nitric oxide synthase (T-NOS) activity. When lysine was in excess (2.25/2.99 group), elevating arginine content (2.54/3.00 group) enhanced growth, antioxidant, and immune performance. Analysis of glutathione metabolism and innate immune-related pathway revealed that an optimal arginine/lysine ratio mitigates inflammatory damage induced by oxidative stress. An arginine/lysine imbalance significantly elevated liver malondialdehyde (MDA) content while reducing total antioxidant capacity (T-AOC), superoxide dismutase (SOD), catalase (CAT) activities, and glutathione (GSH) content, thereby increasing the expression levels of inflammatory factors (IL1B, IL8, TGFB1, BAX). These findings demonstrate that an imbalance in arginine/lysine adversely affects the growth, metabolism, and antioxidant capacity of largemouth bass. When lysine is in excess, increasing the arginine content to achieve an arginine/lysine ratio of 0.85 alleviates the negative effects of antagonism, suggesting arginine supplementation may regulate oxidative damage caused by lysine excess.