Hepatic Oxidative and Metabolic Responses and Histopathology of Red Tilapia ( Oreochromis spp.) to Acute Salinity Stress

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As freshwater resources become increasingly limited, the expansion of aquaculture into brackish environments necessitates a deeper understanding of salinity stress tolerance in economically important species. Red tilapia ( Oreochromis spp.) is widely cultured due to its relative salinity tolerance; however, the hepatic physiological and molecular responses underlying acute salinity stress remain insufficiently characterized. In this study, red tilapia were maintained in freshwater (0.0‰, control) or exposed to saline water (17.7‰ ± 0.1‰) and sampled at multiple time points to evaluate liver histopathology, biochemical parameters, oxidative stress markers, and gene expression responses. The 192‐h LC 50 was estimated at 17.74‰, with a pronounced mortality window observed between 48 and 96 h of exposure. Acute salinity stress induced marked hepatotoxicity, characterized by oxidative damage and metabolic dysregulation. Antioxidant enzymes, including superoxide dismutase (SOD) and catalase (CAT), exhibited a biphasic response, with early activation followed by significant depletion, accompanied by progressive lipid peroxidation indicated by elevated malondialdehyde (MDA) levels. Concurrent metabolic disturbances were evidenced by increased lactate dehydrogenase (LDH) activity, hyperglycemia, altered lipid profiles, and histological steatosis. Elevated hepatic cortisol levels further confirmed a localized stress response. Gene expression analysis across five time points revealed significant upregulation of lta4h , ltc4s , cbr1 , soat1 , and cyp24a1 in the salinity‐exposed group. Gene expression analysis across five time points revealed significant upregulation of lta4h , ltc4s , cbr1 , soat1 , and cyp24a1 in the salinity‐exposed group. The altered expression of genes associated with arachidonic acid metabolism and steroid biosynthesis suggests their involvement in inflammation and lipid metabolic imbalance under salinity stress. These results demonstrate that acute salinity exposure triggers a time‐dependent pathological cascade in the liver of red tilapia involving oxidative stress, metabolic disruption, and inflammatory activation. This integrated physiological and molecular framework provides valuable insight into salinity‐induced hepatotoxicity and offers potential targets for improving salinity tolerance in tilapia aquaculture.