Effects of replacement of fish meal by soybean meal on growth characters of Siganidae(<I>Siganus guttatus</I>)

Abstract

A 49-day feeding experiment was conducted to evaluate the effects of replacement of fish meal by soybean meal in Siganus guttatus[with the initial weight(104.64±2.76)g]diets on fish growth performance,body composition and biological indices and to determine the optimum soybean meal concentration in S.guttatus diets.Five isonitrogenous and isoenergetic diets were formulated containing 35% protein and 19.00 MJ/kg gross energy.The replacement ratio(soybean meal∶fish meal)was 0∶1(D1),1∶2(D2),1∶1(D3),2∶1(D4),1∶0(D5).S.guttatus which were fed to satiate twice daily,were cultured in conical rearing tanks(0.5 m3)with 25 ind per tank and three replications per group.The results showed that the growth performance of S.guttatus was significantly affected by the concentration of soybean meal in the diets.Weight Gain(WG),Special Growth Rate(SGR)and Feed Intake(FI)had a negative correlation with diet soybean meal concentration.WG and SGR were maximized when fish were fed with pure fish meal,24.42% and 0.44 %/d,respectively.Significant differences were observed in SGR in each group.The value of FI in D1 was significantly higher than that in D5.Feed Conversion Rate(FCR)had a positive correlation with diet soybean meal concentration.The lowest value of FCR was found in D1,but there was no significant difference between D1 and D2.There was also no obvious difference between D2 and D3.The replacement had no significant effects on muscle crude protein and moisture but had marked influence on whole body crude protein and fat.The lowest value of whole body crude protein was observed in D5(19.11%).Liver crude protein content tended to increase first and then decrease,with increasing soybean meal concentration in dietsi.Liver crude fat in higher soybean meal concentration diets is significantly lower than in lower soybean meal concentration diets.The replacement had no significant effect on biological indices except Viscerasomatic Index.The replacement ration should be less than 1∶2 in S.guttatus diets based on SGR,FCR,FI and some other parameters.However,considering the muscle quality of S.guttatus,it is indicated that the replacement ratio could amount to 2∶1.