| The early life cycle of fish can be divided into the embryonic,larval,and juvenile stages.In addition to the essential nutrients for growth provided by the early embryo’s endogenous nutrition,i.e.the yolk,the other stages have to absorb food and other nutrients from the external environment to grow and reproduce normally.The fish living environment is usually divided into natural waters and artificial aquaculture waters.Fish in natural waters are likely to be starved for a long time due to temperature changes,food distribution differences,predation competition among species,ecological environment damage and many other reasons.However,in the artificial aquaculture environment,the factory aquaculture leads to high aquaculture density,resulting in uneven feeding of baits,pollution of the aquaculture environment and other factors that cause hunger.Short-term starvation may cause fish growth lag,immature gonadal development,and affect digestion and the immune system.Long-term starvation may even cause a large number of fish death.Therefore,it is of practical production needs and academic significance to study the effects of different starvation stress on fish.Because of this,this study used the hybrid offspring of Epinephelus fuscoguttatus（♀）and Epinephelus polyphekadion（♂）as experimental materials to study the changes of digestive tract enzyme activities liver and muscle nutrient components and leptin gene expression of juvenile grouper under short-term starvation.The research results obtained are as follows:1.Effects of short-term starvation on digestive enzyme activities and serum biochemical indexes of juvenile hybrid grouper.In hybrid grouper（Epinephelus fuscoguttatus♀×E.polyphekadion♂）in young fish as experimental material,At a salinity of 27.0±1.0,the water temperature is28.0±1.0℃,6.0±1.0mg·L-1dissolved oxygen and under the condition of the hybrid grouper juvenile fish for short-term hunger processing 0d,5d,10d and 15d,which were divided into S0 group,S5 group,S10 group and S15 group,and S0 group was used as the control group,were determined hybrid grouper juvenile fish digestive enzyme activity and serum index.The results showed that digestive enzymes’activities decreased with the prolonging of starvation time,and the activities of amylase increased first and then decreased.Serum carbohydrate,cholesterol,triglyceride,total protein,albumin and other biochemical indexes decreased significantly（P<0.01）and maintained at a relatively stable level（P<0.05）.The activities of aspartate aminotransferase（AST）,alanine aminotransferase（ALT）and alkaline phosphatase（ALP）showed a zigzag step decrease（P<0.05）.According to the analysis,in the process of short-term starvation,juvenile hybrid grouper mainly consumed carbohydrate and fatty substances in the early stage and metabolized energy based on protein in the later stage to maintain life activities,and short-term starvation did not cause irreversible liver damage to hybrid grouper.2.Effects of short-term starvation on the contents of amino acids and fatty acids in tissues of juvenile hybrid grouper.At a salinity of 27.0±1.0℃and a water temperature of 28.0±1.0℃,juvenile hybrid grouper were treated with short-term starvation for 0d,5d,10d and 15d,which were divided into S0 group,S5 group,S10 group and S15 group,respectively,and S0group was used as the control group.The results were as follows:（1）With the prolonging of starvation time,the total amino acids and essential amino acids in the liver of hybrid grouper showed a wave-like change,which first increased and then decreased.（2）With the prolongation of starvation time,the total amino acids in juvenile hybrid grouper muscle decreased at first and then increasing,while the essential amino acids showed a linear increase.The flavour amino acid（FAA）and umami amino acid（DAA）showed a trend of decreasing first and then increasing,and the maximum value of FAA and DAA reached 30.07%and 21.70%on ten days after starvation.（3）During starvation,the saturated fatty acid（SFA）in the liver of hybrid grouper showed a"down-up-down"trend;Monounsaturated fatty acid（MUFA）showed a trend of continuous decrease.Polyunsaturated fatty acids（PUFA）showed a linear upward trend.（4）Fatty acid SFA in the liver of hybrid grouper increased during starvation;MUFA and PUFA showed a trend of increasing first and then decreasing and reaching the maximum values in the S5 group,23.43%and 28.31%,respectively.The results showed that the hybrid grouper had strong adaptability to starvation and mainly consumed lipids in the early starvation period.When the lipids consumption reached the threshold,the fish began to consume amino acids for energy supply.3.Effects of short-term starvation on leptin gene expression in different tissues of juvenile hybrid grouper.In this study,the control group（0d）and the starvation group（5,10,15d）were set,and the liver,intestinal tract,stomach,kidney,brain and muscle were collected after the end of starvation.The expression of the leptin gene in six tissues was analyzed by real-time quantitative PCR（q RT-PCR）.The leptin gene in liver tissue was significantly decreased with the prolonging of starvation time（P<0.05）.The level of intestinal tissue in the control group was higher than that in a hungry group（P<0.05）;The gastric tissue decreased first and then increased,and reached the highest value 15days after starvation（P<0.05）;It increased first and then decreased in renal tissue,and reached the highest value at five days after starvation（P<0.05）;There was no significant difference between the hungry groups in brain tissue（P>0.05）;There was no significant difference in muscle tissue（P>0.05）.The results showed that the leptin gene expression was mainly high in liver tissue,decreased intestine,stomach,brain and kidney,and minor in muscle tissue.Short-term starvation had a significant effect on the Leptin gene of hybrid grouper.In conclusion,this study took juvenile hybrid grouper as the experimental object.On the one hand,the effects of starvation stress on the digestive tract’s enzyme activities,including liver,intestine,and stomach of juvenile hybrid grouper,were explored from the biochemical and nutritional levels.On the other hand,the changes of gene expression levels in different tissues of juvenile hybrid grouper under short-term starvation were preliminarily studied at the molecular level.The goal is to explain the biological process and molecular regulation mechanism of hunger adaptation of hybrid grouper and provide a theoretical basis for studying fish starvation adaptation. |
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