Effects Of Low Temperature Stress On Blood Physiological And Biochemical Indexes Of Oreochromis Hornorum

In the present study, the effects of low temperature stree on blood physiological and biochemical indexes of Oreochromis hornorum with different fatness were investigated in the recirculating aquaculture system, and the results are as following:1. Semilethal low temperature of Oreochromis hornorum90 individuals with average weight of 105g were randomly divided into three groups, and water temperatures were decreased from 25℃to the temperature at which fish died out at the rate of 1℃/ 24 hours. Prosit analysisvshowed that the semilethal low temperature of Oreochromis hornorum was 10.78℃, and the range of low lethal temperature was from 13.7℃to 8.6℃.2. Effects of Low temperature stress on behavior, morphological, blood physiological and biochemical indexes of Oreochromis hornorumA stress trial was conducted to investigate the effects of different low temperatures (25℃, 20℃, 18℃, 16℃and 14℃) on behavior, morphological, blood physiological and biochemical indexes of Oreochromis hornorum with different fatness in the recirculating aquaculture system. 450 individuals with average weight of 113g(high fatness)and 104g(low fatness)were randomly divided into 5 groups. Fish were fed at each tank with different temperature and sampled every 10 days. The results are as follows:Feeding, swimming speed, breathing frequency and the responses to outside stimuli of Oreochromis hornorum were reduced as temperatures decresed; Fish stopped feeding below 16°C, and fish began to die at 14°C as stress time extended; Specifically, fish with low and high fatness survived for 22 and 31 days, respectively, under the stress of 14°C. Body fatness, fat body coefficient, HIS and VSI decreased obviously during the process of the low temperature stress, and the biggest reduction was found in HIS.As temperatures decreased, Red blood cells, hemoglobin, white blood cells and lymphocytes of Oreochromis hornorum reduced significantly during the first 30 days (p<0.05). At the end of experiments, the physiological indexes recovered to the initial levels except fish with low-fatness in 16°C group.ALT and AST activities in serum fluctuated during the process of temperature stress. At 20°C, ALT and AST activities decreased slowly, and significantly lower than the initial levels at the end of experiment (p<0.05). At 18°C and 16°C, ALT and AST activities increased significantly (p<0.05), and then recovered slowly to the initial level at the end of experiments. However, ALT and AST activities at 14°C increased all through the process of stress and were significantly (p<0.05) higher than the levels of control group at the end of the experiment.At 20°C and18°C, activities of serum CK increased significantly at first (p <0.05),and then decreased slowly and recovered to the initial level, except fish with high-fatness at 18°C after the stress; At 16°C, activities of serum CK of fish with low-fatness increased at first and then recovered to the initial level at the end of the experiment, while activities of serum CK of fish with high-fatness increased significantly all the time (p <0.05), and significantly (p < 0.05) higher than level of the control group after the stress; At 14°C, activities of serum CK in experimental groups were significantly (p<0.05) higher than level of the control group. Activities of serum LDH increased significantly (p <0.05) at first 10 days, and then recovered to initial levels, while the peak activities of serum LDH at 14°C was obviously higher than that of other treatments.Blood glucose content in the groups of 20°C, 18°C and 16°C decreased obviously at the first 10 day, but no significant difference was found(p﹥0.05), and from the 10th to 50th day the content remained the same level; At 14°C, two content peaks of fish with high-fatness were found at the 10th and 30th day, while blood glucose content of fish with low-fatness presented a descending trend. Serum total protein and serum albumin at 20°C and 18°C did not change significantly during the process of the stress, but obviously decreased in the groups of 16°C and 14°C. Serum TBIL content of group 14°C significantly (p <0.05) increased as the time extended, while in other experimental groups, serum TBIL content increased significantly (p <0.05) at first then recovered to the initial levels. Serum CHOL and serum TG content of all treatments showed a descending trend compared with the control groups, and the most significant decrease was foung in 14°C group.No significant difference was found in serum K+ of all experimental groups during the process of stress. Na+, Cl-, Ca2+ content in serum at 14°C was significantly (p <0.05) decreased as stress time extended, while no significant difference was found in other experimental groups.3. The difference of tolerance to acute low temperature between Oreochromis hornorum with different fatness120 indiveiduals with average weight of 125g (high fatness) and 115g (low fatness), were randomly divieded into four experimental tanks with different water temperatures (16℃, 14℃, 13℃and 12℃) and stressed for 72 hours. The difference of tolerance to acute low temperature between Oreochromis hornorum with different fatness was analyzed by comparison of the T50 values (stress time until death rate to 50%).At 16℃, no dead fish was found in the two experimental groups. At 14℃, 13℃and 12℃, the T50 values of fish with low-fatness was significantly higher than that of fish with high-fatness. T-test analysis showed that tolerance to acute low temperature of fish with low-fatness was significantly stronger than that of fish with high-fatness.