Effects Of Low Temperature Stress On Physiolgy，Biochemical And Fatty Acid Of Epinephelus Coioides

Semi-lethal low temperature of different temperature acclimation groups of Epinepheluscoioides was studied in this paper via experiments of rapid freezing and slow freezing.Thispaper mainly studied on the effects of low temperature stress on food intake，growth，morphology index，serology index and fatty acid composition of different temperatureacclimation groups of Epinephelus coioides through slow freezing experiment and aimed tofind out the reason of weak cold hardiness of Epinephelus coioides.1.Semi-lethal low temperature of Epinephelus coioideIn this experiment,120uniform sized fish(healthy and strong,average weight50±0.23g，breeding at25℃water temperature) were selected and divided into two temperature coolinggroups,rapid freezing group and slow freezing group.Each temperature cooling group wasthen divdied into three groups.Water temperatures of the three groups weredecreased/increased by1℃/24h and seperately reached to the given beginning temperature：20℃，25℃，30℃.Fish were breeded at the given water temperature for two weeks.And thenwater temperatures were decreased by1℃/24h in slow freezing groups and1℃/h in rapidfreezing groups until fish all died.The results indicated that: semi-lethal low temperatures of20℃，25℃，30℃temperature acclimation groups in rapid freezing experiment were12.2℃，10.21℃，9.42℃；semi-lethal low temperatures of20℃，25℃，30℃temperature acclimationgroups in slow cooling experiment were8.13℃，8.68℃，10.4℃.2.Effect of low temperature stress on food intake、growth、morphology index and musclecontent of Epinephelus coioideIn this experiment，400uniform sized fish(healthy and strong,average weight130g) wereselected and divided into three temperature acclimation groups(20℃，25℃，30℃groups) andone control group breeding at the25℃water temperature.Fish of different groups were rearedin different given water temperatures for two weeks and water temperature in different groupswere decreased at the speed of1℃/h to17℃，which was keeped for15days.Sample takingwas conducted every5days.The results indicated that:food intake of Epinephelus coioidedecreased with water temperature decreasing.Fish stopped feeding at16℃.At the end of thisexperiment， indexs of fish in control group changed little. Body weight，fatness，hepatosomatic index and viscerasomatic index of fish in different temperature acclimationgroups decreased. Body weight， fatness of fish in different groups decreased unsignificantly,while the hepatosomatic index and viscerasomatic index in30℃groupsdecreased significantly.After this experiment, crude protein levels and crude lipid levels ofmuscle in all groups decreased in the mass, moisture levels of muscle increased. Crudeprotein levels of muscle in20℃groups decreased significantly after experiment，while25℃and30℃groups decreased unsignificantly. Crude lipid levels of muscle in all groupsdecreased significantly and moisture levels of muscle in all groups increased significantly.Theresults showed under low temperature，lipid in muscle as the main energy source wasconsumed，moisture levels in muscle increased relatively.Besides,lipid in muscle as well as inabdominal fat was consumed to satisfy energy requirment in30℃groups,which showed thatfish in30℃groups gave a stronger stress response under low temperature stress.3．Effect of low temperature stress on serology indexes of Epinephelus coioideIn this experiment，the effect of low temperature stress on serology indexes of differenttemperature acclimation groups of orange-spot grouper (Epinephelus coioides) were studied.The glucose aspartate aminotransferase (AST), aspartate aminotransferase (ALT), lactatedehydrogenase (LDH),total protein (TP), albumin (ALB), total bilirubin(TBIL), glucose(GLU),triglyceride (TG), and total cholesterol (TCHOL) were determined.The resultsindicated：after this experiment，indexes of control groups changed little.On the whole，serumprotein decreased，activity of AST、ALT、LDH increased，GLU and TBILI content increased，CHOLcontent decreased,TG decreased at the first and increased later.Besides,after experiment, serum protein in30℃groups was differently less than that of other two groups,while activity of ALT、AST、LDH and TBILcontent in30℃groups were differently more than those of other two groups，which hinted fish in30℃groups gave a stronger stress response under low temperature stress.4．Effect of low temperature stress on fatty acid composition of Epinephelus coioideIn this experiment，the effect of low temperature stress on fatty acid composition ofdifferent temperature acclimation groups of orange-spot grouper (Epinephelus coioides) wasstudied.The results indicated：after this experiment，in20℃groups，the content of PUFA、MUFA and UFA/SFA increased；in30℃groups，the content of PUFA and UFA/SFAdecreased；in25℃groups，the content of UFA decreased while UFA/SFA changed little.Theresults showed that there was low temperature lipid metabolism adaptation mechanism in the20℃group in this experiment，which was not found in25℃and30℃groups.This mayexplain why fish in20℃temperature acclimation group had a lower semi-lethal lowtemperature than that of other two groups.5. Effect of low temperature stress on the activity of antioxidant enzymes of EpinepheluscoioideIn this experiment，the effect of low temperature stress on the activity of antioxidant enzymes SOD and CAT in different temperature acclimation groups of orange-spot grouper(Epinephelus coioides) were studied.The results showed：at the earlier period of experiment，the activity of SOD and CAT in all groups decreased unsignificantly.But the activity of SODand CAT in all groups increased significantly with the time going on,and it was differentlymore than that of control group.After this experiment，no significant difference of the activityof SOD and CAT was found among these groups.