Low-temperature induced neuro-oxidative stress and metabolic reprogramming in the brain of juvenile fourfinger threadfin (Eleutheronema tetradactylum)

<title>Abstract</title> <p> Temperature is a critical environmental factor influencing fish growth, metabolism, and overall physiological homeostasis. Although the fourfinger threadfin ( <italic>Eleutheronema tetradactylum</italic> ) is a warm-water fish of significant economic value, the molecular mechanisms underlying its central nervous system's response to prolonged cold stress remain poorly understood. To elucidate the pathological and metabolic regulatory mechanisms of the brain under cold stress, juvenile <italic>E. tetradactylum</italic> were exposed to a low temperature of 18°C for 7 and 14 days, respectively. An integrated approach combining histopathology, antioxidant enzyme assays, and liquid chromatography-mass spectrometry (LC-MS/MS) metabolomics was employed. Histological analysis revealed that prolonged cold stress induced severe pathological damage, including blurred neuronal boundaries, nuclear condensation, and elevated cytoplasmic vacuolation, which peaked at day 7 and remained significantly high at day 14. Biochemically, the antioxidant defense system exhibited a dynamic pattern of early inhibition and limited late-stage compensation. Levels of malondialdehyde (MDA) fell on day 7, along with a simultaneous drop in the activities of catalase (CAT), glutathione peroxidase (GPx) and superoxide dismutase (SOD). This suggests that an adaptive metabolic depression may have occurred. However, by day 14, while SOD partially recovered, CAT and GPx remained inhibited. This functional uncoupling of the antioxidant cascade resulted in a significant surge in MDA levels, indicating severe late-stage lipid peroxidation. Metabolomic profiling identified 248 and 222 differentially accumulated metabolites in the 7-day and 14-day groups, respectively. Key biomarkers, such as 1-oleoyl-sn-glycero-3-phosphocholine, α-ergocryptine, and various lysophosphatidylcholines, drove the metabolic distinction between groups. KEGG pathway analysis revealed persistent disruptions in cysteine and methionine metabolism, amino acid biosynthesis, and glycerophospholipid metabolism under cold stress. These findings suggest that <italic>E. tetradactylum</italic> attempts to adapt to cold stress by reprogramming amino acid metabolism to bolster energy supply and antioxidant capacity, and by modulating glycerophospholipid metabolism to maintain membrane fluidity. Ultimately, this study provided novel insights into the neuro-metabolic regulation of cold adaptation in this species, offering a theoretical foundation for breeding cold-tolerant strains and mitigating overwintering risks in aquaculture. </p>