Effect Of Tributyrin On Growth Performance And Disease Resistance Of Crucian Carp(Carassius Auratus Gibelio) And Its Mechanism

With the flourish of the aquaculture industry and the increase of intensive degree,the use of antibiotics in the breeding process has brought benefits,but also caused a series of drawbacks,which seriously hindered the sustainable development of aquaculture,even endangered human health.During this period,many nutritional additives or non-nutritional additives came into being.Tributyrin,as a short-chain fatty acid ester,has been widely used as feed additive in livestock and poultry,but its application in aquatic animals and its mechanism of action are rarely reported.In this paper,the effects of different doses of Tributyrin on growth performance,immune function,intestinal structure and disease resistance of crucian carp(Carassius auratus gibelio)were studied by 8-week growth experiment.High-throughput sequencing technology was used to further study differentially expressed genes related to Tributyrin of crucian carp,revealing the effect of tributyrin on growth of crucian carp and its Mechanism.The main results of this study were as follows:1.Effects of Tributyrin on Growth Performance,Liver Function and Disease Resistance of Crucian Carp(Carassius auratus gibelio)A basal diet was formulated as control,and 4 experimental diets were formulated by adding 0.5g/kg,1g/kg,1.5g/kg,2g/kg tributyrin(TB)in the basal diet,respectively.A total of 450 healthy crucian carp with similar weight body weight(43.58 ±1.6)g were randomly divided into 5 groups with 3 replicates per group and 30 fish per replicate.The adaptation period lasted for 2week and the formal period lasted for 8weeks.At the end of the culture experiment,the relative percent survival of Aeromonas hydrophila in 96 hours was detected by infection test.The results showed that the growth performance in experimental groups was improved totally,and the difference on weight gain rate(WGR)and sepcific growth rate(SGR)were significantly increasebetween 1 g/kg,1.5 g/kgTB and control group(p<0.05),but decrease significantly on feed conversion ratio(FCR)(p<0.05),the addition of 1 g/kg TB was the best;There was no significant difference in GOT and GPT in hepatopancreas between the experimental groups and the control group(p>0.05),the GOT and GPT activities were decreased in serum,and GOT was significant difference from the control group.(p <0.05).After infection with Aeromonas hydrophila,the relative protection rates(RPS)of each test group were 26.08%,45.31%,56.65%,and 40.74%,respectively,and the highest RPS was at 1.5 g/kg TB.The above results indicated that long-term feeding with tributyrin-addes feed can enhance the growth performance of crucian carp,not only protect hepatopancreas,but also enhance transaminase activity and disease resistance.2.Effect of Tributyrin on Morphology of Intestinal Mucosa and Immune indexes of Crucian Carp(Carassius auratus gibelio)After the culture test,the tissues were taken out and determined.The results showed thatwhen the dosage was 1 g/kg,the intestinal villus height was significantly higher than that of control group,the crypt depth was significantly reduced.The villus height/crypt depth of control group was lower than other groups,and the muscularis thickness of each test group was significantly different from that of the control group except the 2g/kg TB group(p<0.05).The head kidney index and spleen index in experimental groups were higher those in control group(p<0.05),and when the doses are in the range of 0.5~1.0 g/kg,they were significantly higher than the control group.When the content of Tributyrin was 1 g/kg,the activities of LSZ,ACP,AKP,SOD and CAT in serum and hepatopancreas were significantly increased,and the contents of NO and MDA were significantly decreased.The above results show that Tributyrin can accelerate the digestion and absorption of nutrients in the intestine to a certain extent,enhance metabolic capacity,promote intestinal development and repair,then promote the growth of the body.3.Study on the Mechanism of Tributyrin in Promoting Growth of Crucian Carp(Carassius auratus gibelio)In order to explore the mechanism of Tributyrin in promoting growth of crucian carp,the intestine of 1g/kgTB treatment group and control group were constructed and sequenced.A total of 2705 differentially expressed genes were obtained including 522up-regulated genes and 2183 down-regulated genes.GO functional enrichment analysis showed that the expression of genes involved in amide biosynthetic process andorganonitrogen compound metabolic process were up-regulated.KEGG pathway shows that in addition to affecting the material metabolism pathway,it also affected mTOR signaling pathway.Tributyrin can activate the mTOR signaling pathway by increasing insulin-like growth factor I and serine/threonine protein kinase,thus improving the utilization of protein in fish feed,promoting intestinal protein synthesis and epithelial cell growth.At the same time,insulin-like growth factor I can promote the release of insulin,combining with the specific receptors on pancreatic acinar cells,which can accelerate the secretion of enzymes such as lipase and trypsin,further accelerate the decomposition and utilization of tributyrin,enhance the absorption and utilization of electrolyte and water,enhance the immune function of fish,and achieve the effect of promoting growth.