Physiological, immune responses and liver lipid metabolism of orange-spotted grouper (Epinephelus coioides) under cold stress

Low temperature is an important environmental factor in aquaculture. Cold stress has caused great economic loss in fish culture worldwide. In the present study, we investigated the effects of low temperature on biochemical parameters, DNA damage, immune and lipid metabolism related genes expression in orange spotted grouper. In the experiment, water temperature decreased from 28 °C to 13 °C at a rate of 1 °C/h, and keep 13 °C for 48 h. Fish blood and liver were collected at 28 °C, 22 °C, 19 °C, 16 °C, 13 °C and 13 °C for 0 h, 3 h, 6 h, 12 h, 24 h and 48 h. The results showed that low temperature decreased total blood cell count and led to DNA damage. Biochemical parameters such as GLU significantly declined in fish under low temperature, while a significant increase in AST, ALT and LDH was observed. The relative expression of genes related to lipid metabolism, such as CPT-1, SCD-1 and FABP10, were significantly induced by low temperature stress. Furthermore, the expression of apoptotic related genes including caspase3, caspase8, caspase9 and BCL-2 were up-regulated, suggesting that caspase-dependent pathway could play important roles in low temperature-induced apoptosis in fish. Moreover, the gene expression of inflammatory cytokines such as IL-1α and IL-1R were significantly increased, whereas MHC-1 mRNA levels were significantly decreased. These results indicated that cold stress could lead to a decrease in blood cell count, DNA damage and liver dysfunction, and increase liver lipid metabolism, apoptosis and inflammation-related gene expression in orange spotted grouper.