Abstract:Low temperature tolerance of Epinephelus moara♀× E. lanceolatus♂(hereinafter Yunlong) was investigated in this study. The initial water temperature (20℃) was served as control, and then was dropped at a rate of 1℃/d, the changes in serum biochemical indices and metabolic enzyme activities of Yunlong were determined when the water temperatures reached 16℃, 15℃, 13℃ and 10℃. During the cold stress period, survival rates and the semi-lethal temperatures of Yunlong, E. fuscoguttatus♀× E.lanceolatus♂ (Pearl Gentian), and E. coioides♀ × E. lanceolatus♂(Qinglong) were observed and recorded. The semi-lethal temperature was recorded when the survival rate reached 50%. We found that the semi-lethal temperatures for Pearl Gentian, Qinglong and Yunlong were 11℃, 9.5℃, 9℃, and 8℃ respectively. The levels of serum creatinine (CREA) and total cholesterol (T-CHO) were first increased and then decreased along with increase of the intensity and duration of the low temperature stress. The level of serum triglycerides (TG) fluctuated at different temperatures, and the values at 15℃ and 10℃ were significantly different from that of the control group (P<0.05). The content of serum glucose (GLU) also varied with the temperatures, the levels at 16℃ and 13℃ were different from that of the control group (P<0.05). The activity of serum alkaline phosphatase (AKP) at 16℃ was slightly and insignificantly increased (P>0.05). The activity of serum catalase (CAT) fluctuated and showed significant differences between the control group and low temperatures at 16℃, 15℃ and 10℃ (P<0.05). The activity of serum glutamic-oxaloacetic transaminase (GOT) was slightly higher than that of the control group (P>0.05). The activity of serum glutamate pyruvate transaminase (GPT) was elevated followed by a decline along with the increase in the intensity and duration of low temperature stress. At 16℃ and 15℃, the activity of GPT was different from that of the control group (P<0.05). In conclusion, Yunlong was the most tolerant to low temperature stress among the three hybrids. Our data also suggested that low temperature could impair the immunity and the antioxidant capacity of juvenile fish, therefore the intensity and duration of the low temperature condition should be limited during practice.
