How Dietary Methionine Shields Golden Pompano ( Trachinotus ovatus ) From Cold‐Stress Triads via Nrf2 Activation?

This study evaluated the physiological and molecular mechanisms underlying cold stress tolerance in golden pompano ( Trachinotus ovatus ) after a 56‐day feeding trial with high‐lipid diets (18%) supplemented with varying methionine (Met) levels (1.04%, 1.14%, 1.24%, 1.34%, 1.44%, 1.54%, and 1.64%). After the feeding period, fish fed 1.24% Met (HLM3) exhibited the highest thermal growth coefficient (TGC) and relative growth rate (RGR), together with the lowest feed conversion ratio (FCR) among all treatments ( p < 0.05). Survival remained 100% across all dietary groups throughout the feeding period. Afterwards, 10 fish from each cage selected randomly were subjected to a 96‐h cold stress from 19.30 ± 0.06°C to 14.38 ± 0.01°C to assess survival, lipid metabolism, antioxidant capacity, immune function, ferroptosis, inflammation, and apoptosis. T. ovatus in the HLM3 group exhibited significantly reduced serum levels of total cholesterol, triglycerides, LDL‐C, AST, ALT, and NEFAs, accompanied by elevated antioxidant enzyme activities (SOD, CAT, T‐AOC, and GSH‐Px) and lower MDA and ROS levels ( p < 0.05). Immune parameters (IgM, LZM, ACP, and AKP) were also markedly enhanced in HLM3. Moreover, hepatic Met and cysteine levels were higher in HLM3, while hepatic lipid deposition was suppressed. Lipolytic ( cpt1a , atgl , lpl , and pparα ) and antioxidant genes ( nrf2 , ho-1 , gxp4 , and MnSOD ) were upregulated, along with increased NADP + /NADPH ratio and downregulation of keap1 . S lc7a11 , bcl2 , and bcl-xl genes were elevated, while ferroptosis and apoptosis markers were alleviated. Overall, dietary inclusion of 1.24% Met in an 18% high‐lipid diet enhanced the nrf2 ‐mediated antioxidant defense, lipid catabolism, and antiferroptotic pathways, thereby improving cold stress resilience in T. ovatus .