Short-term cold stress effects on antioxidant, metabolic, and immune responses in the red and white muscles of juvenile yellowfin tuna (Thunnus albacares)

This study aimed to examine the physiological responses of juvenile yellowfin tuna ( Thunnus albacares ) to short-term cold stress by comparing oxidative stress, metabolic regulation, and immune-related transcriptional responses in red and white muscles under two low-temperature conditions (24 °C and 18 °C) and a control temperature (30 °C). Juvenile tuna were exposed to these temperature conditions for 36 h, and muscle samples were collected at multiple time points to assess enzyme activities, biochemical indicators, and gene expression. Antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px), exhibited a biphasic response, characterized by an initial upregulation at 18 °C after 12 h followed by a decline under prolonged cold exposure. Elevated malondialdehyde (MDA) levels in the red muscle at 24 h indicated enhanced lipid peroxidation and oxidative stress. At 36 h, increased activities of aspartate aminotransferase (AST), alanine aminotransferase (ALT), and acid phosphatase (ACP) in the red muscle reflected altered metabolic status and enhanced involvement of amino acid-related processes, whereas reduced lactate dehydrogenase (LDH) activity suggested suppression of anaerobic metabolic capacity under prolonged cold stress. Gene expression analysis revealed tissue-specific responses: the red muscle showed a pronounced and sustained induction of hspa1b and acadm , while the white muscle exhibited a faster but less persistent transcriptional response. In addition, the immune-related gene irf3 was downregulated in the red muscle but transiently upregulated in the white muscle. Overall, red muscle displayed slower yet more sustained regulation, whereas white muscle responded more rapidly but exhibited greater sensitivity to cold-induced biochemical perturbations. These findings highlight time- and tissue-specific mechanisms underlying tuna muscle responses to cold stress and provide insights relevant to adaptive management strategies for pelagic fish under climate change scenarios.