The Influence Of Weaning On Feeding And Liver Fat Metabolism Of Yangtze Sturgeon

The Yangtze sturgeon(Acipenser dabryanus)is a national-level protected animal in China.,which has been achieved full artificial reproduction.However,improper weaning can seriously affect the growth and survive of juvenile fish during the breeding process.Although some studies have investigated the effects of weaning on fish growth,most of them have focused on their effects on body length and weight.Little is known about the underlying molecular mechanism.Therefore,in this study,a model of juvenile Yangtze Sturgeons with successful and unsuccessful feeding transfer was established to compare and analyze their effects on feeding and lipid metabolism of juvenile Yangtze sturgeons by combining morphology,transcriptome and molecular techniques.The main results are as follows:Compared with the successful weaning of juveniles(nor-feeding),the body length and body weight of the weaning failure juveniles(non-feeding)was significantly reduced(P<0.05);the liver was atrophy,gallbladder enlarged;liver cells were closely arranged,the boundaries were blurred,the cytoplasm was deeply stained;Hemosiderin deposits and Kupffer cells increase is appear around the sinusoids.The activity of aspartate aminotransferase(AST)and alanine aminotransferase(ALT)in non-feeding fish liver was increased significantly(P<0.05).The RNA-seq results showed that 4959 and 3212 differentially expressed genes(DEGs)were screened in the brain and liver,respectively.These DEGs were significantly enriched in GO terms such as channel activity,hormone activity,biosynthesis process,and fat synthesis.KEGG enrichment results showed that DEGs in the brain were significantly enriched in pathways such as neuroactive ligand-receptor interaction,adipocytokine signaling pathway and PI3K-Akt signaling pathway,and DEGs in the liver were significantly enriched in steroid biosynthesis,TNF signaling pathway,and fatty acid biosynthesis.These results indicated that the failure of weaning will significantly affect the growth,the health of the liver,endocrine,and fat metabolism of Yangtze sturgeon juveniles.To further explore the effects of weaning on the feeding and fat metabolism,the Yangtze sturgeon of 60 days post-hatching(60 dph)were randomly divided into 3 groups for weaning experiment,including the control group(feeding with tubificidae),the weaning group(feeding with artificial diet),and the re-feeding group(fed with artificial feed for 5 days and then fed with tubificidae),each group has 3 parallels,and the test period is 10 days.The expression of feeding regulation factors in the brain,as well as key enzymes and transcriptional regulators of fat metabolism in the liver at different time points(1,3,5,6,8,and 10 days)were analyzed.The main findings are shown as follows:Compared with the control group,the expression of the orexigenic factor AgRP in the weaning group was significantly reduced in the early stage(1-3 days)(P<0.05),and significantly increased after the 5th day(P<0.05),the expression of NPY increased on day3-8,and decreased significantly on day 10(P<0.05).In the re-feeding group,the expression of both AgRP and NPY increased significantly(P<0.05).In addition,the expression of the anorectic factor CART increased significantly(P<0.05)in the early stage(1-3 days)of the weaning,and then decreased significantly(P<0.05),while POMC only increased significantly on the 10 th day after the weaning,the other time points were significantly reduced(P<0.05),and the expression of both increased significantly after re-feeding the tubificidae.These results indicate that the expression of appetite-stimulating factors(AgRP,NPY)and anorectic factors(CART,POMC)in the brains of the Yangtze sturgeon after weaning were significantly different than that of the untransformed juveniles.In addition,compared with the control group,the expression of ACC1,FAS,ATGL and SREBP1 was significantly(P<0.05)reduced in the weaning group,and increased after re-feeding;the expression of CPT1 was significantly(P<0.05)increased,and the PPARγincreased significantly(P<0.05)in the early stage(1-3 days)of the weaning,and decreased in the later stage;the expression of CPT1 increased after re-feeding the tubificidae,but PPARγ decreased significantly(P<0.05).The above results indicate that the fatty acid oxidation and decomposition in the liver were promoted after the conversion to the artificial diet,and the fatty acid synthesis process was inhibited to meet the functional requirements,and the fatty acid synthesis increased after the re-feeding of the tubificida in Yangze sturgon.Conclusion: The failure of weaning will significantly affect the transcription levels of endocrine and fat metabolism-related factors in the brain and liver of Yangtze sturgeon juveniles,thereby affecting growth.Specifically,the failure of diversion may affect the growth of Yangtze sturgeon through the following two aspects.On the one hand,it may partly promote the expression of appetite factors in the brain and inhibit the expression of anorexia factors;on the other hand,it may promote the expression of genes related to the oxidation of fatty acids in the liver and inhibit the expression of genes related to fat synthesis,thus affecting the health of the liver and the appetite of animals,reducing the food intake of animals,and thereby inhibiting growth of Yangtze sturgeon.