| Difference of growth stage,food distribution,seasons or environmental changes(larva breeding,temporary rearing and live transportation,etc.)will lead to food shortages and starvation for fish in artificial culture.Fish regulates metabolism,energy distribution and energy consumption to adapt to hunger.This process makes effects on fish growth,metabolism,morphology and tissue structure,reproduction,blood biochemical index and digestive enzyme activity.This paper studies the muscle nutrition composition,digestive enzyme activity and ghrelin gene expression of Juvenile Larimichthys crocea.The following is a detailed introduction.1.Effect of fasting on amino acids and fatty acids of juvenile L.crocea.To investigate the effect of starvation on muscle amino acids and fatty acids in juvenile large yellow croaker L.crocea,(Method)540 healthy fish with similar body weight(40.80±3.40g)were selected for experiment.The muscle were sampled from experimental fish after 0,4,8,12,16,and 20 days of starvation for chemical analysis,respectively.(Result)Results showed that starvation significantly affected methionine content(P<0.05),which reached the lowest content(0.48±0.12%)after 8 days of starved and obtained the highest content(1.62±0.23%)after 16 d starved.However,the other 15 kinds of amino acids showed no significant difference during the groups(P>0.05),with the same trends of increased at first and then decreased when prolonging the starvation time.Also,the non-essential amino acids,essential amino acids,flavored amino acids,essential amino acids and total amino acids showed the same changing trends as the 15 kinds of amino acids.As to fatty acid,starvation had significant effects on the fatty acid content in muscle of juvenile L.crocea(P<0.05).Among them,saturated fatty acids(SFA)increased first and then decreased with the prolongation of starvation,and reached the maximum content after 8 days of starvation(30.90±0.28%);monounsaturated fatty acid(MUFA)content among different treatment groups had no significant difference(P>0.05),but all the treatment groups were slightly larger than that of the control group(starvation for 0 day);polyunsaturated fatty acid(PUFA)content showed an increasing trend after the first drop,and the lowest value was in the group of starvation for 12 days(31.87 ± 0.65%).(Conclusion)From the above research results,we can know that the amino acid and fatty acid contents in the muscle related to meat quality can be changed by proper starvation treatment,which can improve the meat flavor of the L.crocea.2.Effect of fast on digestion enzyme activity of juvenile large yellow croaker.In order to determine the effect of starvation on the digestive enzyme activity of Larimichthys crocea juvenile,540 juvenile individuals with body weight about 40 g were divided into six groups(S0,S4,S8,S12,S16,and S20,three replicates and 30 fish individuals each)and fasted for 0,4,8,12,16,and 20 d,respectively,0 as the control.After being fasted,nine fish individuals each group,3 each replicate were sampled for stomach and intestine digestive enzyme activity analyses.The analyzed included protease,lipase and amylase activities.The results showed that the activities of digestive enzymes in both stomach and intestine were influenced by fast significantly.The activities of three types of enzymes in both stomach and intestine all decreased sharply in the first 4 days of fast by 28.32-71.85%,after that turned to rise to different extents.The digestive enzyme activities in stomach increased greatly from day 4 to day 20 while the activities of lipase and amylase in intestine rose from day 4 to day 8 and that of protease from day 4 to day 12,and then all the activities decreased.The activities of lipase and amylase in stomach were lower than those in intestine whereas the protease activity in stomach was higher than that in intestine,indicating that the food in stomach was digested limitedly by lipase and amylase.In addition,the ranges of protease and lipase activities in stomach(-6.71%~63.72% for protease,-62.88%~29.91% for lipase)were narrower than those in intestine(-64.79%~71.85% for protease,-232.17%~46.28% for lipase)whereas the range of amylase activity in stomach(-81.71%~36.92%)was higher than that in intestine(2.35%~45.41%).Thus,the effect of fast on the activities of protease and lipase in stomach were lower than that in intestine whereas the effect on amylase activity in stomach was higher than that in intestine.Furthermore,the amylase activity was lower than the protease and lipase activities in both stomach and intestine,suggesting that the lipase and protease were the main digestive enzymes involved in metabolism when L.crocea juvenile were starved whereas the amylase was less important for metabolism.Our findings clarified the behavior of digestive enzymes in both stomach and intestine when L.crocea juvenile were starved,which should aid to the healthy culture of L.crocea.3.Effects of fasting on the expression of ghrelin in L.crocea Juveniles.According to the known ghrelin gene sequence of L.crocea,the specific primers were designed and the expression level was determined by real-time quantitative PCR.The results showed that the expression of ghrelin was the highest in stomach followed by the muscle,and low expression in the other tissues.The expression of ghrelin in stomach increased gradually after starving started,and the expression increased to the highest after 8 days' starvation,then gradually decreased because of starvation longer.The ghrelin expression in intestine and brain increased at beginning,and then reduced and increased again.Ghrelin expression both in kidney and muscle increased at first,and then decreased to the lowest after 12 days' starvation.The above results show that the proper fasting of juvenile L.crocea can improve the meat quality,and provide the basic information for the improvement of the quality improvement to artificial culture of L.crocea.In addition the changes of digestive enzyme activity and ghrelin gene expression in juvenile L.crocea on fasting revealed the dynamic regulation process of juvenile L.crocea adapted to the starvation stress.On the one hand,it provides reference for the study of digestive enzymes and ghrelin genes.On the other hand,by studying the digestive enzyme activity and gene expression of ghrelin in juvenile large yellow croaker of different stages of hunger,to find the juvenile large yellow croaker in the process of adapting to hunger stress index best time,implementing scientific and rational feeding for the health of large yellow croaker breeding has important theoretical guiding significance. |
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