| The present experiment investigated the effects of starvation and refeeding on the growth,nonspecific immunity and intestinal microorganism of juvenile hybrid grouper.A single factor experimental was designed,the experimental group(fast-refeeding)and control group(normal feeding)were set,three replicates were set in each group,each of which contained 30 fish.Hybrid grouper with an average initial body weight of(74.16 ±12.08g)were fed over a period of 60 days,the first 30 days were the starvation period,and the fish were treated with starvation in the experimental group,and the fish were fed with normal in the control group,the last 30 days were the recovery period,and the fish were fed with satiety in the experimental group for 30 days,and the fish were fed with satiety in the control group.By detecting the body weight,body length,intestinal digestive enzyme activity,serum antioxidant enzyme activity,serum lipid content,spleen immune-related gene expression and intestinal microbiome of fish,the following results were obtained:1.The growth of hybrid grouper: starvation significantly affected the growth indexes of fish body(p<0.05).In the starvation stage,the feeding rate(FR)of fish was significantly higher in the experimental group than that of the control group(p<0.05),and the feeding rate of fish reached about 11.19% in the experimental group at the end of the experiment.The Final body mass of the fish was significantly lower in the experimental group than that in the control group(p<0.05).At the end of the experiment,the average body weight of the fish reached at 144.51 g in the experimental group,while that of fish reached at 178.09 g in the control group.The specific growth rate(SGR),condition factor(CF)and weight gain rate(WGR)of fish were all lower in the experimental group than those in the control group,but there was no significant difference(p>0.05).2.The nutrition composition of hybrid grouper: starvation significantly affected the nutritional composition of fish in the muscle(p<0.05).During the starvation stage,the content of fat significantly decreased in the experimental group(p<0.05).the content of fatwas 0.97% in the experimental group,the content of fat was 1.57% in the control group,the content of moisture significantly increased in the experimental group(p<0.05),the content of moisture was 80.32% in the experimental group,the content of moisture was76.88% in the control group.During the recovery feeding period,refeeding could restore the fat level of the fish muscle,the content of fat increased significantly in the fish of the experimental group(p<0.05),and the content of fat reached 1.54%,while the content of moisture decreased significantly in the fish muscle of the experimental group(p<0.05)and the content of moisture was 76.29% in the experimental group.There was no significant change in the nutritional composition of fish muscle in the control group(p>0.05).3.The activities of intestinal amylase,lipase and protease were significantly decreased the experimental group(p<0.05),among which the lowest activity of amylase was 0.11(U/mg*prot),the lowest activity of lipase was 25.75(U/mg*prot),and the lowest activity of protease was 5.94(U/mg*prot).During the recovery feeding period,refeeding could significantly improve the activity of digestive enzymes,the activity of lipase was significantly higher(p<0.05),the activity of lipase and protease was slowed down after rising first,respectively peak at 36.20(U/mg*prot)and 14.41(U/mg*prot),and the activity of amylase was slow rise and peak at 0.21(U/mg*prot)in the experimental group.there was no significant change in intestinal digestive enzyme activity in the control group(p>0.05).4.The biochemical indices of hybrid grouper: hunger significantly influence lipid in the fish(p<0.05),during the short term hunger stage(15 days),high density lipoprotein cholesterol(HDL-C),low density lipoprotein cholesterol(LDL-C)and triglycerides(TG)levels have no significant change in the serum(p>0.05),during the starvation for a long time period(30 days),the content of HDL-C,LDL-C and TG significantly decreased(p<0.05)in the experimental group,which the content of TG reduced to 9.29(mmol/m L),respectively the content of HDL and LDL-C dropped to the lowest 1.41(mmol/m L)and 1.07(mmol/m L),during the refeeding period,refeeding would increase the content of lipid in the serum of fish in the experimental group(p<0.05).The content of HDL-C increased first and then decreased in the serum of fish in the experimental group(p>0.05),while the content of LDL-C increased slowly.There was no significant difference in the content of HDL-C,LDL-C and TG in the serum in the control group(p>0.05).5.The non-specific immunity of hybrid grouper: hunger significantly affected fish non-specific immune(p<0.05),in hunger phase,compared with the control group,the activities superoxidation disproportionation(SOD),glutathione peroxidase(GSH-PX)andlysozyme(LYM)and catalase(CAT)were significantly increased before they are significantly lower in the experimental group(p<0.05),the expression of IL-17 and IFN-γwere compared with the control group significantly decreased(p<0.05)in the experimental group,refeeding could obviously improve the non-specific immune in the experimental,the activities of SOD,GSH-PX,LYM and CAT increased during feeding again(p<0.05),refeeding after 15 days,the expression of IFN-γ and IL-1β were increased significantly(p<0.05)in the experimental group,while the expression of IFN-γ,TNF-α and IL-1βsignificantly reduced(p<0.05)in refeeding after 30 days,which were restored to the control group.During the experiment,there was no significant change in the activity of antioxidant enzyme and the expression of immune genes in the control group(p>0.05).6.The intestinal microorganism of hybrid grouper: starvation significantly affected the abundance and species of intestinal microorganisms in fish(p<0.05).Refeeding can supplement the abundance and species of intestinal microorganisms in fish to a certain extent.During the feeding recovery stage,the abundance and species of fish in the experimental group were significantly lower than those in the control group(p<0.05). |
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