Effects Of Replacement Of Dietary Fish Meal By Soybean Meal On Growth Performance,Digestive Enzyme Activities And Intestinal Tract Structure Of Bullfrog,Rana (Lithobates) Catesbeiana

This experiment was conducted to investigate the effect of replacement of fish meal with soybean meal on growth performance,feed utilization,physical indicators,body composition,amino acid composition of whole body and muscle,digestive enzyme activities,hepatic biochemical indexes and intestinal tract structure of bullfrog,Rana(Lithobates)catesbeiana.Bullfrogs were randomly assigned to 6 groups of 20 bullfrogs per replicate and fed the experimental diets for 60 days.Six isonitrogenous and isoenergetic diets were formulated to contain different levels of soybean meal based upon the basal diet to replace fish meal 0(D1),20%(D2),40%(D3),60%(D4),80%(D5)and 100%(D6).All the experimental bullfrogs were fed twice to apparent satiation daily.Results of the study were presented as follows:1.Effects of replacement of fish meal by soybean meal on growth performance and body composition of bullfrogs.The results showed that the weight gain rate(WGR),specific growth rate(SGR),protein efficiency ratio(PER)and protein productive value(PPV)were highest(458.37%,2.91%/d,2.92%,47.71%,respectively),and the feed conversion ratio(FCR)was the lowest(0.88)when the replacement ratio of fish meal by soybean meal was 60%(P<0.05).The WGR,SGR,PER and PPV were significantly lower when dietary 100% fish meal was replaced by soybean meal,while FCR was significantly higher than that of the other groups(P<0.05).There were no significant difference among groups of feeding rate(FR),survival rate(SR),hepatic somatic index(HSI)and viscera somatic index(VSI)(P>0.05).Compared to the control group,hind leg index(HLI)decreased with the dietary soybean meal increased(P<0.05).There were no differences on contents of moisture,crude protein,crude ash of bullfrog hind leg muscle among all treatments,however,crude protein content in body was significantly lower in the groups fed with D5 and D6(P<0.05),crude lipid content in body was significantly lower in the groups fed with D6 than D1(P<0.05).The amino acid composition of whole body and hind leg showed no significant difference among all the groups(P>0.05).2.Effects of replacement of fish meal with soybean meal on the digestive enzyme activities and hepatic biochemical indexes of bullfrogs.Compared to the control group,the activity of proteases declined,amylases increased,lipases firstly increased then declined,with dietary soybean meal level increased(P<0.05).The proteases of D5 and D6 were significantly lower than that of the other groups(P<0.05),and the amylases of D6 was significantly higher than that of D1(P<0.05),and the lipases of D1,D2 and D3,were significantly lower than that of D4 and D5(P<0.05).Moreover,the superoxide dismutase(SOD)declined and catalases activity(CAT)firstly increased then declined with the dietary soybean meal level increased(P<0.05).The highest value of SOD or CAT was showed in D4 or D1 group,respectively(P<0.05).No significant difference was found on hepatic malondialdehyde(MDA)among all the experiment groups.3.Effects of replacement of fish meal by soybean meal on the intestinal tract structure of bullfrogs.The intestinal tract structure of bullfrogs showed no significant difference when the replacement ratio with soybean meal was less than 80%(P>0.05),and the structure presented as normal,and the intestinal villus grew well with many goblet cells.However,the replacement ratio with soybean meal was 100%,the thinner intestinal wall,shorter and lower volume of intestinal villus,and damaged epithelial cells was observed in bullfrog fed the diet with none fishmeal supplementation.