| The temperature of aquatic ecosystems is affected by many factors such as climate,latitude,season and water depth,which inevitablely occur fluctuation.It is important for research on fish acclimation to temperature changes.Schizothorax prenanti,a cold-water commercial fish endemic to China,grows in a watershed with low water temperature.Its growth is slow and its sexual maturity is late,so it is difficult to recover stock resources once declined.And the higher water temperature conditions are not conducive to the survival of the fish.Therefore,in terms of expanding its artificial breeding,it also faces restrictions on temperature and related conditions such as geography and climate.How to improve the heat tolerance and growth ability of the squid is always a problem to be solved in resource conservation and artificial breeding.In order to elucidate the effects of different temperature acclimation on the heat tolerance,growth metabolism and antioxidant function in Schizothorax prenanti.The present study,four acclimation temperatures of lower?17??,suitable?22??,higher?27??,and day and night fluctuations?17-27??were set.In this experiment,300Schizothorax prenanti with an average body weight of 1.97±0.13 g and a body length of 6.3±0.18 cm were placed in a circulating filtered water aeration system of the same specification.These Schizothorax prenanti were subjected to constant and fluctuating temperature acclimation for 28 days.Each group was fed twice a day at a fixed time each day.On the 4th,14th and 28th day of acclimation,the expression levels of growth regulation genes?IGF-1,GH?and heat stress related genes?HSP70?and the activity of detecting key enzymes of glucose metabolism and antioxidants in different temperature groups were detected.The aim of this study is to understand the effects of heat tolerance,growth performance,glucose metabolism and antioxidant function of acclimated fish in different water temperatures.The main results are as follows.?1?Effects of different acclimation temperatures on the heat tolerance of Schizothorax prenanti and HSP70 gene expression in the liver.?1?The critical high temperature(CT max)and lethal high temperature(LT max)values of the fish increased with the acclimation temperature rise.The critical low temperature(CT min)and lethal low temperature(LT min)values decreased with decreasing acclimation temperature decline.?2?Under the acclimation conditions of 17-27?,the temperature tolerance range(CT max-CT min)of the fish was significantly broadened than that of the 17?,22? and 27? constant temperature groups respectively.?3?In the temperature range of 17-27?,the heat-tolerant area of the fish is 294.7?2.The acclimation reaction rate of the fish in the low temperature stage?17-22??is higher than that in the high temperature stage?22-27??.The low temperature acclimation reaction rate is significantly lower than the low temperature stage in the high temperature range.?4?HSP70 gene expression in the liver of Schizothorax prenanti was not sensitive to low temperature,in contrast,sensitive to high temperature 27?,and increased significantly at 4 days.Liver HSP70 gene expression was not sensitive to low temperature 17? and fluctuating temperature stimulation,and gradually increased with the number of acclimation days,and increased significantly until 28 days.The results indicated that the fluctuating temperature 17-27? acclimated,which significantly improved the temperature tolerance range and heat tolerance capability of Schizothorax prenanti.?2?Effects of different temperatures acclimation on growth performance,digestion and absorption,and brain GH and liver IGF-I genes expression in Schizothorax prenanti.?1?The specific growth rate?SGR?and weight gain rate?WGR?of these accilimation groups were affected by temperature,the results were:17-27??22?>17?>27?.There was a significant difference between the groups of constant temperature acclimation,and the food intake was positively correlated with its specific growth rate.?2?The crude protein content of whole fish in 17? group was significantly higher than that in other groups.The crude fat content 22? and fluctuating temperature group was significantly higher than other groups.The water contant and crude ash content in 27? group was significantly higher than that in the other groups.?3?Different acclimation temperatures had significant effects on intestinal digestion and enzyme activities,and the trypsin activity was 17-27?>22?>27?>17?.The lipase activity in 22? and 27? group was significantly higher than that in the 17? and fluctuating temperature groups.The intestinal amylase activity was highest in 22? group.The activities of intestinal creatine kinase and glutamyl transpeptidase fluctuating temperature group were significantly higher than those of the three constant temperature groups.The Na+,K+-ATPase activity was highest in the17? group.?4?The foregut villi of the 22? group and the fluctuating temperature group were relatively thick,and the foregut villi appeared to shrink and declined in number in 27? group.?5?Brain GH and Liver IGF-1 gene expression of the fish was significantly affected by acclimation temperatures.GH expression was positively correlated with the acclimation temperature.Liver IGF-1 gene was highly expressed under the conditions of fluctuating temperature of 17-27? and moderate temperature of 22?.Significant down-regulation at high temperature 27? and low temperature17?.The study found that the trend of GH gene expression in the brain of each group changed with time and the expression of IGF-1 gene in the liver was similar and synergistic.IGF-1 gene expression was positively correlated with the growth performance indexes,which suggested that IGF-1 plays a more direct role in the regulation of growth than GH during temperature acclimation.The results showed that the intestinal digestive and absorption enzyme activities of the fish were higher under the water temperature conditions of 22? and 17-27?.The intestinal morphology was healthy,and the crucial gene of promoting growth GH and IGF-1 expression levels were significantly up-regulated,which.effectively promoted growth of Schizothorax prenanti.?3?Effects of different acclimation temperature on glycogen content and glucose metabolism enzyme activity in Schizothorax prenanti.?1?Liver glycogen content in 27? group was the highest,and the glycogen content in the fluctuating temperature group was the lowest.The muscle glycogen content in 22? group was the highest,and the muscle glycogen content was the lowest in 17? group.?2?As the acclimation temperature increases,the liver glycolysis related enzymes,the activity of hexokinase?HK?decreased,and the activities of pyruvate kinase?PK?and citrate synthase?CS?increased.The activity of fructose-6-phosphokinase?PFK?increased first and then decreased,while the activities of HK and PK in muscle was opposite to that of liver.The activities of PFK,PK and CS in the fluctuating temperature group were significantly higher than those in the 22? group.?3?With the increase of acclimation temperature,the activity of hepatic gluconeogenesis related enzyme activites,such as fructose 1,6-monophosphatase?FBP?and glucose-6-phosphatase?G-6-Pase?increased first and then decreased;In muscle,FBP activity increased with increasing acclimation temperature,and G-6-Pase activity decreased.The activities of FBP and G-6-Pase in the liver and muscle of the fluctuating temperature group were significantly lower than those in 22? group.The above results indicated that the ability to utilize the glycogen lysis for energy supplying in the fluctuating temperature group is improved,and the ability to synthesize and store glycogen reduced in Schizothorax prenanti.?4?Effects of different acclimation temperatures on the activities of tissue antioxidant enzymes in Schizothorax prenanti.?1?The activities of superoxide dismutase?SOD?,catalase?CAT?and glutathione peroxidase?GSH-Px?in liver and muscle tissues in 27? group increased overwith acclimation time.The activity of antioxidant enzymes in the intestines was opposite,and the content of malondialdehyde?MDA?in the intestines and muscles increased over.At the 28th day of acclimation,the MDA content in the muscle was significantly higher than that in the other groups.The activities of SOD and CAT in the liver and intestine of the fluctuating temperature group increased over time.At the 28th day of acclimation,the MDA content and CAT activity in the liver were significantly higher than those in the other groups.The activity of antioxidant enzymes in liver,muscle and intestine of 17? group did not change significantly with the prolongation of acclimation time.On the 28th day of acclimation,there was no significant difference in MDA and SOD activity in the liver from 22?.?2?In 17? group,the total antioxidant capacity?T-AOC?in muscle and intestine decreased with prolonged acclimation time.The T-AOC in the liver and intestine of the fluctuating temperatur group and the muscle in 27? group increased with the acclimation time.On the 28th day of acclimation,the liver T-AOC were 17? group?22? group?variable temperature group>27? group.The muscles were 27? group>variable temperature group>17? group>22? group.Studies have shown that 28? high temperature acclimation at 27? will lead to the reduction of oxidative damage and antioxidant capacity in the intestine of Schizothorax prenanti,and the fluctuating temperature of 17-27? significantly increased the antioxidant capacity of each tissues.In summary,different temperature acclimation has significant effects on heat tolerance,growth metabolism and antioxidant function in Schizothorax prenanti.The constant temperature 22? and 17-27? fluctuating temperature acclimation through up-regulating brain GH and liver IGF-1 gene expressions,promoted fish growth.The fluctuating temperature acclimation was able to improve the temperature tolerance and the digestion and utilization of sugar,and antioxidant capacity of Schizothorax prenanti.These results suggested that the fluctuating temperature acclimation approach could be used to improve Schizothorax prenanti tolerance to high temperature and adaptability in aquaculture practice. |
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