The appropriate dietary methionine content reduces deamination and gluconeogenesis in Chinese perch ( Siniperca chuatsi )

This study evaluated the effects of different dietary methionine (Met) levels on the feeding, growth, and protein metabolism of Chinese perch, Siniperca chuatsi . Six diets containing graded levels of Met (0.88%, 1.11%, 1.68%, 2.02%, 2.27%, and 2.72%) were fed to fish (initial weight: 13.74 ± 0.12 g) for 8 weeks. The results showed that 1.68% dietary Met significantly improved the growth of Chinese perch, with a feeding rate of 3.50 ± 0.19%/d, which was considerably higher than that of the other groups. In the brains of fish fed the diet with 1.68% Met, mRNA expression of the cocaine amphetamine‐regulated transcript gene, an inhibitor of feeding, decreased significantly, which could promote fish appetite and increase feed intake. When the concentration of dietary Met was 1.68%, the processes of deamination and gluconeogenesis were inhibited, showing a decrease in the expression levels of glutamate dehydrogenase ( gdh ), phosphoenolpyruvate carboxykinase ( pepck ), and glucose‐6‐phosphatase ( g6pase ) in the fish liver. Moreover, the expression of genes related to the amino acid catabolism and the AMP‐activated protein kinase (AMPK) pathway was also decreased in the 1.68% dietary Met group, while protein synthesis was promoted and protein decomposition was inhibited. However, when the Met content was more than 2.02%, the feed intake and utilization decreased, resulting in slower growth of Chinese perch. When the Met content reached 2.72%, the weight gain rate (WGR) decreased by about 38.3%, and the specific growth rate (SGR) decreased by about 29.9% compared with fish fed with 1.68% dietary Met. After orthogonal polynomial regression analysis, the recommended dietary Met concentration for Chinese perch ranges from 1.73% to 1.75%, which can improve feed utilization by promoting protein utilization of Chinese perch and reducing gluconeogenesis. Combined with high feed intake, optimal growth can be achieved. This study clarifies Met's role in regulating Chinese perch amino acid metabolism and energy homeostasis, providing a basis for eco‐friendly feeds (reducing ammonia excretion by inhibiting deamination to support sustainable aquaculture). Future studies could explore Met's synergies with other essential amino acids, its requirements under different environmental conditions (e.g., water temperature), or validate its regulation of AAR/TOR pathways via in vitro experiments to deepen the understanding of Met metabolism in carnivorous fish.