Tolerance Of Selenium-yeast,DL-Methionine In Diets Of Largemouth Bass (Micropterus Salmoides)

This study was conducted to investigate the tolerance of largemouth bass(Micropterus salmoides)on Selenium-yeast,DL-Methionine(DL-Met)on the growth performance,biochemical indexes,antioxidant response and histology of liver.On basis of the above studies,the further study was aimed to investigate the tolerance and safety margin in largemouth bass.The results and conclusions are summarized as follows:1.Tolerance of Selenium-yeast in Diets of Largemouth Bass(Micropterus salmoides)A 10-week growth trail was conducted to evaluate the tolerance of Se-yeast in diet of largemouth bass(Micropterus salmoides)on growth performance,hematological,tissues antioxidant response,and histologyof hepatic and intestine.Four experimental diets were prepared with Se-yeast inclusion levels at 0(Y0),0.5(Y0.5),2.5(Y2.5)and 5.0(Y5.0)mg/kg,in which Y0.5 was designed as the maximum recommended level,and the Y2.5 and Y5.0 were 5 and 10 fold levels of Y0.5,respectively.Each diet was fed to 6 replicates with 20 largemouth bass with initial body weight of 12.99±0.01 g in each tank.Fish in Y0 group showed the lowest weight gain rate and feeding rate(P<0.05),but also lowest feed conversion ratio(P<0.05).Se-Yeast inclusion significantly decreased plasma AKP offish(P<0.05).The content of HDL-C in Y0.5 group was significantly higher than that of other groups(P<0.05).Plasma Ig M concentration of Y2.5 and Y5.0 groups were significantly higher thanthat of Y0 and Y0.5 groups(P<0.05),which indicated the inflammation of high Se inclusion group.Compared with Y0 group,plasma MDA was significantly decreased(P<0.05),and glutathione peroxidase(GSH-Px)activitywas significantly increased by Se-yeastsupplementation(P<0.05).Different degrees of liver histological damage were observed inallgroups,and fish fed diets with 0.5 mg/kg Se-yeastrelieved the symptom.The present study shows that the 0.5 mg/kg(Se levels 1.29 mg/kg)Se-yeastcould enhance the lipid metabolism and antioxidant response of largemouth bass in the present study.Fish meal and krill meal contain high levels of Se element,which need to be considered when exogenic Se sources were used.In general,we suggest that the maximum recommended level of Se-yeast is 0.5mg/kg in diets of largemouth bass is safe and the safety margin is 1X in largemouth bass diet.2.Tolerance of DL-Methionine in Diets of Largemouth Bass(Micropterus salmoides)A 10-week growth trail was conducted to evaluate the tolerance of DL-Methionine(DL-Met)in diet of largemouth bass(Micropterus salmoides)on growth performance,hematological,tissues antioxidant response,and hepatic histology.Four experimental diets were prepared with DL-Met supplement levels at 0 %(D0),0.42%(D1),2.1%(D5)and 4.2%(D10),accounted for 1.85%,2.73%,6.25%,10.65% of feed protein,in which D1 was designed as the maximum recommended level,otherwise the D5 and D10 were 5 and 10 fold levels of D1,respectively.Each diet was fed to 6 replicates with 30 largemouth bass initial body weight[(9.67±0.01g)] in each tank.The results showed that:fish in D10 group showed the lowest growth performance(P<0.05).The content of HDL-C in D1 group was significantly higher than that of D5 and D10 groups(P<0.05).Plasma TPRO,GLU and ALT concentration of D5 and D10 groups were significantly higher thanthat of D0 and D1 groups(P<0.05).The content of plasma GSH-Px activity and MDA in D10 group were significantly higher than that of D1 group(P<0.05).Compared with D0 group,liver SOD and GSH-Px activity were significantly enhanced in D1 group(P<0.05).Different degrees of liver histological damage were observed inallgroups,but fish fed diets with 4.2% DL-Metleaded to largemouth bass liver is brown.In D10 group CYP8b1 expression of liver is significantly higher than that of other groups,the bile acid production increased,so it can promote the absorption of cholesterol,but leaded to largemouth bass liver cholestasis disease.Adding DL-Met with largemouth bass to liver cell apoptosis has no obvious improvement.ACC1,CPT1?levels in the liver of D1 groupcan improve the liver fat metabolism disorders,reduce liver fat deposition and maintain normal proliferation of stem cells.Ingeneral,The present study shows that the maximum recommended level of DL-Met is 0.42% in diets of largemouth bass is safe and the safety margin is 5X in largemouth bass diet.