| Channa argus and Channa maculata are important native fish species in our country. They belong to Perciformes, Channoidei, Channidae, Channa. Now, the hybrids accounted for the main amount of the cultivating, becoming the main farming species. Three Channa all have advantages and disadvantages, Channa argus grow fast but do not feed compound feed. Channa maculata can feed compound feed but growth slow. C. maculata♀×C. argus♂, fast growth and feed compound feed, but can not be cultured in wintering in the north, which is difficult to promote. Serum biochemical indexes, digestive enzyme, and liver antioxidant capacity in acute or chronic temperature stress were searched, which could provide some basic data for Channa culture and low temperature stress study. The details are as follows.1. This study showed: in the process of cooling, the behaviors of C. argus, C. maculata, and their hybrids(C. maculata♀×C. argus♂ and C. argus♀×C. maculata♂) were: 18℃ or above, Channa swam normally, up and down in the water or around the wall; 18 ~ 12℃, C. argus and C. argus♀×C. maculata♂ reduced activities slightly, C. maculata and C. maculata♀×C. argus♂ started to swim out of balance; 12 ~ 6℃, the activities of C. argus and C. argus♀×C. maculata♂ were inactive, C. maculata and C. maculata♀×C. argus♂ were in the bottom quietly, no swimming, breathing weakly; when dropped to 6℃, C. maculata in chronic temperature stress began to die; when dropped to 2℃, all the C. maculata in chronic temperature stress died completely. The results proved that C. maculata was the least resistance to low temperature, it died under 6℃ for a long time. And C. maculata♀×C. argus♂ was the less resistance to low temperature, C. argus and C. argus♀×C. maculata♂ can well adapt to the low temperature environment.2. This study investigated the effects on serum biomarkers in four fish, including Channa argus, Channa maculata, and the hybrids(C. maculata♀×C. argus♂ and C. argus♀×C. maculata♂) caused by low temperature(acute or gradient temperature decreasing). The results showed: with gradient temperature decreasing, the activities of most enzymes were significantly increased in all the Channa(p<0.05), but the activities of GOT in acute temperature decreasing and GGT in gradient temperature decreasing were the opposite(p<0.05). Under the two conditions, acute or gradient temperature stress, the level of TG was apparently decreased, the level of GLU was quite the contrary. The concentration of. serum Na+ and Cl- were significantly decreased(p<0.05) and the change ranges were similar. The amount of total protein(TP) became decrease after the low temperature stress in all fish, but the fluctuation range of C. maculata was the largest, from 26.4±2.91 to 43.1±1.81 mmol·L-1. Compare the two modes, the levels of GOT, GPT, GLU, K+ and Ca2+ in acute temperature stress were higher than that in chornic temperature stress, but the levels of GGT, ALP, LDH, Na+ and Cl- were the opposite. The results proved that the low temperature caused damages on liver and heart at different degrees in all fish and the fluctuations of biochemical indicators were different in two modes. The findings here implied that similar patterns and different physiological changes appeared in C. argus and C. maculata, or the two hybrids, when challenged with low temperature. And serum biochemical parameters could provide some basic data for the low temperature decreasing study in Channa.3. This study showed: under the two modes(acute or gradient temperature stress), the activities of Trypsin in gradient temperature decreasing were significantly decreased(p<0.05). The level of LPS was increased in acute temperature stress. The activities of Pepsin in all fish in acute or gradient temperature stress were apparently increased(p<0.05). The proved that Channa digestive metabolism was affected by the low temperature decreasing, digestive enzyme activities were decreased; with the reduction of temperature, Channa reduced food intake or even not feed, digestive enzymes secreted decreased; long time of low temperature environment may reduce Channa feed conversion rate, and should be alerted in the process of breeding. At the same time, with the temperature descreasing, the fish can adjust their digestive enzyme activities to change metabolic, which to adapt to the environment changes in some degress. The findings here also implied that digestive enzyme parameters in acute or gradient temperature stress provides some reference data for Channa large-scale cultivation, promotion, certain fish diets change and domesticate.4. This study showed: the acticities of SOD, T-AOC and CAT in C. maculate in acute temperature decreasing were significantly increased(p<0.05), similarly the levels of T-AOC and CAT in gradient temperature decreasing; the acticities of SOD, T-AOC and CAT in C. argus and hybrids were decreased. The contents of MDA in C. maculata and hybrids were apparently increased(p<0.05).The contents of GSH in C. argus and hybrids were the opposite, but in C. maculata in acute temperature stress significantly decreased(p<0.05). The findings here implied that different free radicals were appeared in Channa under acute or gradient temperature decreasing. And antioxidant system was also damage in a certain degree. Similar to digestive system, antioxidant system was more sensitive to acute temperature stress, and immune ability under continuous low temperature stress in all fish has a cumulative effect. Dropped to 2℃, the levels of CAT and T-AOC were significantly increased in C. maculata, which could lead to the least resistance to low temperature. And this study provides some theoretical basis for strengthening physiological and biochemical regulation ability, immune protection in Channa under the low temperature environment. |
