Temperature regulated nutrient sensing and metabolism of amino acids in juvenile turbot (Scophthalmus maximus L.)

Temperature is well known as the major environmental factor that influences survival and growth of fish, which are poikilothermic animals. However, it is still unclear about the mechanism that underscores thermal-controlled fish physiology, especially nutritional utilization and metabolism, which are vitally important in aquaculture. In the present study, juvenile turbot was force-fed with amino acid mixture and its postprandial absorption, nutrient sensing and metabolism under low (12, 15 degrees C), optimal (18 degrees C) to high (21, 24 degrees C) temperatures were explored. Intestinal trypsin and lipase activity were highly sensitive to water temperature, and highest under optimal temperatures for turbot, whereas amylase remained constant. Selective groups of intestinal amino acid transporters were upregulated in cold temperatures, but the amino acid absorption capability was increased with rising temperature. The mechanistic target of rapamycin (mTOR) signaling pathway was most active at optimal temperature. Postprandial muscle protein deposition achieved maximum level under optimal temperature. Amino acid catabolic enzymes branched-chain aminotransferase and branched-chain alpha-keto acid dehydrogenase activities were increased with rising temperatures. High temperature increased significantly energy metabolism and stimulated cellular stress in liver. These findings highlight the critical role of temperature in modulating amino acid dynamics, metabolic processes and stress responses in juvenile turbot, providing valuable insights for optimizing aquaculture practices.