包膜丁酸钠对许氏平鲉幼鱼生长性能、免疫、抗氧化能力及食欲调控因子基因表达的影响OA

Butyric acid,as one of the short-chain fatty acids(SCFAs),is primarily produced through the fermentation of carbohydrates by gut microorganisms.Butyric acid exhibits functions such as promoting intestinal cell proliferation,regulating intestinal microecological balance,and modulating lipid metabolism.Due to its volatility and distinctive odor,butyric acid is commonly used as a relatively stable sodium butyrate as a feed additive.Studies have found that sodium butyrate exhibits good growth-promoting and feeding-stimulating effects in aquatic animals such as Trachinotus ovatus,Pelteobagrus fulvidraco,Apostichopus japonicus,and Carassius auratus Pengze.Furthermore,influenced by multiple factors such as dietary habits of species,water temperature for breeding,individual developmental stage,and form of addition,the efficacy of sodium butyrate exhibits significant species specificity and dose dependence. Korean rockfish Sebastes schlegelii,also known as blackhead,is a cold-water,offshore bottom-feeding carnivorous fish and one of the important economic fish species in the northern Yellow Sea.In order to investigate the effects of dietary supplementation with varying levels of sodium butyrate(SB)on growth performance,hepatic immune and antioxidant capacity,and the expression of appetite-regulating genes in juvenile S.schlegelii(33.56±0.08 g),six isonitrogenous and isolipidic experimental diets were formulated by adding 0(D1),0.5 g/kg(D2),1 g/kg(D3),2 g/kg(D4),4 g/kg(D5)or 8 g/kg(D6)of coated sodium butyrate to a basal diet.Each diet was fed to triplicate groups of fish for 60 days.At the end of trial,growth performance,feed utilization and figure indices were calculated.Liver and intestinal were separated for enzyme activities analyzing and inflammatory factor expression levels.To investigate the effect of sodium butyrate on the expression of appetite factors,six fish were anesthetized and dissected from each barrel in Group D1 and Group D5.Samples of liver(lep,cck),intestine(ghrelin),and brain(lepr,cckar,ghsrla)were immediately placed in liquid nitrogen after isolatio.The results demonstrated that weight gain rate(WG),specific growth rate(SGR),and feeding rate(FI)initially increased and then decreased with increasing SB levels,peaking in the D4 group(P＜0.05),while the feed conversion ratio(FCR)significantly increased in the D6 group(P＜0.05).Dietary SB significantly upregulated the relative mRNA expression levels of hepatic growth hormone(gh)and insulin-like growth factor-Ⅰ(igf-Ⅰ).The activities of hepatic superoxide dismutase(SOD),catalase(CAT),and alkaline phosphatase(AKP)initially increased and then decreased,reaching their highest levels in the D4 group(P＜0.05).Hepatic alanine aminotransferase(ALT)and aspartate aminotransferase(AST)activities followed a similar trend.Intestinal interleukin-1β(il-1β)and interleukin-8(il-8)mRNA expression levels initially decreased and then increased,with D4 and D5 groups being significantly lower than D1(P＜0.05).Conversely,transforming growth factor-β(tgf-β)mRNA expression initially increased and then decreased,peaking in the D5 group.Compared to the control group(D1),long-term SB feeding in the highest-performing group(D5)significantly reduced hepatic leptin(lep)and cerebral leptin receptor(lepr)mRNA expression(P＜0.05),while significantly increasing intestinal ghrelin(ghrelin)and cerebral growth hormone secretagogue receptor(ghsrla)mRNA expression(P＜0.05).No significant effects were observed on cholecystokinin(cck)or its receptor(cckar)expression(P＞0.05).In conclusion,dietary SB supplementation enhances growth performance,feed intake,hepatic antioxidant capacity,and intestinal immune function in juvenile S.schlegelii.Furthermore,long-term SB feeding promotes appetite by downregulating leptin and its receptor while upregulating ghrelin expression.Therefore,the recommended dosage of SB in the diet of juveniles S.schlegelii is 2～4 g/kg. The experimental results indicate that low-dose(0.2％-0.4％)sodium butyrate serves as a"signal molecule"and energy source within the organism,whereas high-dose(＞0.6％)sodium butyrate behaves more like a"stressor".This dose-dependent bidirectional effect embodies the biological characteristics of sodium butyrate.Low-dose sodium butyrate,through"signal transduction"and"nutrient supply",synergistically acts at three levels:the liver,central nervous system,and intestine,creating a healthier internal environment with more efficient metabolism and lower inflammation levels,ultimately promoting feeding and growth.The positive effects of high-dose sodium butyrate(≥0.6％)reach a plateau and begin to decline,and may even produce negative effects.Firstly,strong acid stimulation and palatability can reduce animal feed intake,lower pH in the stomach and foregut,and inhibit digestive enzyme activity.Secondly,high concentrations of sodium butyrate are toxic to cells,inducing apoptosis(programmed cell death)and generating excessive reactive oxygen species(ROS),which can exacerbate oxidative stress.Furthermore,high-dose sodium butyrate indiscriminately inhibits or even kills various bacteria,leading to dysbiosis.