The Application Of Surfactin In GIFT Tilapia Feed

The effects of dietary surfactin on the growth performance,activities of digestive enzymes,serum biochemical indexes,enzymes of lipid metabolism and hepatopancreas antioxidant ability of tilapia(GIFT,Oreochromis niloticus)were evaluated.The effects of surfactin,bile acids and lecithin on tilapia growth were also investigated.The results of this study could provide a basis for the application of surfactin in fish feed.1.Effects of dietary surfactin on the growth,serum biochemical indexes,enzymes of lipid metabolism and hepatopancreas antioxidant ability of GIFT tilapiaTwo hundred and forty fish with initial average weight of(12.01±0.12)g were randomly divided into four treatment groups with four replicates in each treatment group and 15 fish in each replicate.The fish of four treatment groups were fed experimental diets supplemented with0(control group),50,100 and 200 mg/kg surfactin on the basis of basal diet,respectively.The trial period was 49 days.Compared with control group,final body weight,weight gain rate,specific growth rate and protein efficiency ratio were significantly increased by surfactin supplementation(P<0.05),and feed conversion rate was significantly decreased(P<0.05).The activities of lipase and protease(except the 200 mg/kg groups)in intestinal tract were significantly increased by surfactin supplementation(P<0.05).Compared with control group,the levels of blood urea nitrogen and triglyceride of 50 mg/kg surfactin supplementation group and100 mg/kg surfactin supplementation group were significantly decreased(P<0.05).The glutamic-pyruvic transaminase activity of 50 mg/kg surfactin supplementation group was significantly lower than that of other groups(P<0.05),the glutamic-oxalacetic transaminease activity of control group was significantly higher than that of other groups(P<0.05).All the surfactin supplementation groups had higher activities of lysozyme and alkaline phosphatase compared to control group(P<0.05).The fatty acid synthetase activity of each surfactin supplementation groups were significantly decreased(P<0.05)and the activities of hepatic lipase,lipoprotein lipase and total lipase were significantly increased(P<0.05).The levels of hepatopancreas malondialdehyde were significantly decreased by surfactin supplementation except the 200 mg/kg group(P<0.05).Fish fed diets with 50-200 mg/kg surfactin had a higher activities of total antioxidant capacity,superoxide dismutase and catalase than those of control group(P<0.05).These results demonstrated that the recommended dietary surfactin supplementation level was 50 mg/kg,which could improve the activities of digestive enzymes,regulate serum biochemical indexes,enzymes of lipid metabolism and enhance hepatopancreas antioxidant ability of GIFT tilapia under this experimental condition.2.Effects of surfactin,bile acids and lecithin on the growth,serum biochemical indexes,enzymes of lipid metabolism and health indicators of hepatopancreas of GIFT tilapia.Three hundred and twenty GIFT tilapias with initial average weight of(2.00±0.05 g)were randomly divided into four treatment groups with four replicates in each group and 20 fish in each replicate.The four treatment groups were control group(the basal diet),surfactin group(the basal diet+50 mg/kg surfactin),bile acids group(the basal diet+300 mg/kg bile acids)and lecithin group(the basal diet+500 mg/kg),respectively.The experiment lasted for 56 days.There were significant promotion effects on tilapia growth by dietary surfactin supplementation or bile acids supplementation(P<0.05),no significant difference was found between the two groups(P>0.05).There was no significant promotion effect on the growth of tilapia by lecithin supplementation(P>0.05).The activities of lipase and protease in intestinal tract were significantly increased by surfactin supplementation,bile acids or lecithin,respectively(P<0.05).The blood urea nitrogen level of surfactin supplementation group was the lowest among all groups(P<0.05).The activties of glutamic-oxalacetic transaminease and glutamic-pyruvic transaminase of surfactin supplementation group and bile acids supplementation group were significantly higher than those of control group and lecithin supplementation group(P<0.05).Compared with the control group and lecithin group,the total cholesterol level of surfactin supplementation group was significantly decreased(P<0.05).The triglyceride level of control group was highest among all groups(P<0.05).Compared with the control group,high density lipoprotein cholesterol level and high density lipoprotein cholesterol/low density lipoprotein cholesterol of bile acids group were significantly increased(P<0.05),but no significant differences were found in surfactin supplementation group and lecithin supplementation group(P>0.05).The nonestesterified fatty acid level of surfactin supplementation group,bile acids supplementation group and lecithin supplementation group were significantly increased(P<0.05),and the nonestesterified fatty acid level of the bile acids group was significantly higher than that of the other two groups(P<0.05).Compared with the control group,the activities of fatty acid synthetase and acetyl CoA carboxylase of surfactin group,bile acids group and lecithin group were significantly decreased(P<0.05),no significant difference was found among the three groups(P>0.05).The activities of and total lipase of surfactin supplementation group and bile acids supplementation group were significantly increased(P<0.05),no significant difference was observed in lecithin supplementation group(P>0.05).Compared with the control group and lecithin supplementation group,the activities of lipoprotein lipase of surfactin supplementationgroup were significantly increased(P<0.05),no significant difference was found between surfactin supplementation group and bile acids supplementation group(P>0.05).The activities of superoxide dismutase,catalase and total antioxidant capacity level were significantly improved by surfactin or bile acids supplementation(P<0.05),levels of malondialdehyde were decreased significantly(P<0.05).The glutathion peroxide activity of bile acids supplementation group was significantly increased compared with other groups(P<0.05).The levels of reactive oxygen species in control group was significantly higher than that of others groups(P<0.05).The hepatopancreas cell membrane structures were integrated,and the nucleus was clearly visible,the hepatopancreas tissue fat vacuoles of control group were increased obviously.Fat content of body and muscle were improved by bile acids supplementation(P<0.05),the muscle fat content of surfactin supplementation group was significantly decreased(P<0.05).It was concluded from the above results that 50 mg/kg surfactin supplementation level or 300 mg/kg bile acids supplementation level in diet of tilapia colud promote the growth of fish and have beneficial effects on physiological and biochemical indexes,and no significant difference was found between the two groups.While 500 mg/kg lecithin supplementation level in tilapia diet has no significant promotion effect on fish growth,some physiological and biochemical indexes of GIFT tilapia were improved.