SALINITY EFFECTS ON STRATEGIES OF CARBOHYDRATE METABOLISM IN MILKFISH LIVERS UNDER LOW-TEMPERATURE STRESS

The milkfish (Chanos chanos) is an important aquaculture species in Southeast Asia, they are tropical species and intolerant of water temperature below 12°C. In winter, the cold snap leading to high mortality and huge economic loss has been reported for several decades in Taiwan. The euryhaline milkfish can survive in fresh water (FW) and seawater (SW) environment, whereas the fishermen prefer to culture in FW due to better feed conversion rate. Acclimation of milkfish to SW or FW induces a variety of physiological responses, including changes in their tolerance to low-temperature stress. SW milkfish was found to exhibit better hypothermal tolerance than FW milkfish in the previous study. Under cold stress, reduction of appetite led to loss of energy source in organisms, and hepatic glycogen plays a crucial role in providing energy supply for the whole body. In carbohydrate metabolism, the ATP production via aerobic metabolism was important for detox function of the liver. Our studies revealed that SW milkfish under cold stress (18°C) have the ability to keep consistent energy supply. On the other hand, when the FW milkfish were under cold stress, the hepatic glycogen degradation and gluconeogenesis occurred to maintain the constancy of blood glucose levels and ATP production was reduced due to down-regulation of aerobic metabolism. In addition, the energy flow of TCA cycle inclined to amino acid biosynthesis. Salinity together with low-temperature challenge may lead to a more stressful condition that affected strategies of carbohydrate metabolism.