| In nature,it is very common for fish to be subjected to starvation due to seasonal changes,drastic environmental changes or other man-made factors.Even under the condition of modern artificial rearing,fish may suffer from starvation due to the factors such as too high rearing density,change of weather and unreasonable feeding strategy.Studies have shown that starvation could affect the growth of fish,tissue structure,enzyme activity and immune function,induce a variety of diseases,and even lead to death.But some studies also have shown that dietary restrictions help mammals cope with autoimmune diseases,and that restricting or depriving fish of food may reduce the risk of disease-related mortality in fish.However,studies on the effect of starvation stress on fish immune function are still lacking.In this study,zebrafish(Danio Rerio)and Megalobrama amblycephala were used to study the effects of starvation stress on immune function of fish.We investigated the effects of starvation stress on the liver and gut structure,the immune-related enzymes activity and the expression pattern of genes related to the TLR-My D88-NFκB pathway,and the effects on body weight and gut microbes of M.amblycephala.These works contribute to the understanding of the effects of starvation stress on the immune function of fish,thus providing scientific data and theoretical basis for the prevention and treatment of commercial fish diseases and healthy fish farming.The main findings are as follows:1.The body weight of M.amblycephala decreased significantly with the increase of starvation time.The body weight of M.amblycephala did not decrease significantly when it was starved for 1,4,7 days.The weight loss rate of M.amblycephala was11.98%,15.38% and 18.25% after 14,21 and 28 days of starvation,respectively.2.Starvation stress could affect the liver and intestinal tissue structure of zebrafish and M.amblycephala.With the increase of starvation time,the folds in the intestine decreased,the height of villi decreased,the villi ruptured,the compact arrangement of columnar cells decreased,but the number of goblet cells increased.In the liver,the compact arrangement of cells decreased,the cell atrophy and volume decreased,the nucleus location shifted,and inflammatory cells,intracellular vacuoles and cell rupture gradually appeared.3.Starvation stress affected the activities of immune-related enzymes in the liver and intestine of zebrafish and M.amblycephala.Under short-term starvation,the AKP and ACP activities of the zebrafish intestine decreased significantly,while the SOD and CAT activities increased significantly.CAT activity decreased significantly under longterm starvation.The AKP,ACP and CAT activity in the intestine of M.amblycephala decreased under short-term starvation stress,but the activity of AKP and ACP increased significantly,and the SOD activity decreased significantly under long-term starvation stress.After short-term starvation,the AKP and ACP in the liver of zebrafish and M.amblycephala increased significantly,and the SOD and CAT activities decreased significantly.4.Starvation stress affected the expression of genes related to the TLR-My D88-NFκB pathway in the liver and intestine of zebrafish and M.amblycephala.The expression of IL-1β and TNF-α increased under short-term starvation stress,and then decreased slightly,but finally increased significantly under long-term starvation stress.While in the liver,they decreased significantly under short-term starvation stress,increased under long-term starvation stress.5.Starvation stress affected the microbial community structure and function in the gut of M.amblycephala.In all treatments,Proteobacteria and Fusobacteriota had the highest relative abundance,and the proportions of them at different starvation time of0,4,7,14,21 and 28 days were 56.26% and 36.47%,23.54% and 43.45%,21.23% and36.46%,43.26% and 34.95%,23.73% and 23.07%,48.19% and 29.45%,respectively.Results of LEf Se analysis showed that bacteria associated with inflammatory response such as TM7 A and Saccharimonadales were significantly enriched in group C0(starvation for 7 days),and there was no significant microbial enrichment in the D0(starvation for 14 days)group.The results of functional prediction showed that longterm starvation stress significantly enhanced lipid metabolism,xenobiotics biodegradation and metabolism,metabolism of terpenoids and polyketides.In conclusion,starvation stress could change the liver and intestine structure in zebrafish and M.amblycephala,and affect their immune function by affecting the activities of immune-related enzymes and the expression of genes related to TLRMy D88-NFκB pathway.At the same time,starvation stress could affect the intestinal microbial community structure and function of M.amblycephala,and may further affect its intestinal immune function.The TLR-My D88-NFκB pathway may play an important role in this process. |
