Effects of replacement of fishmeal by alfalfa protein concentrate on growth performance, body composition, and blood biochemistry in juvenile starry flounder, Platichthys stellatus

Abstract

We evaluated the effects of fishmeal substitution with alfalfa protein concentrate on growth,body composition,and blood biochemistry in juvenile starry flounder.We formulated six isonitrogenous and isoener-getic diets,in which fishmeal protein was replaced by alfalfa protein concentrate in the following proportions: 0%(S0),10%(S10),20%(S20),30%(S30),40%(S40),50%(S50).Specific growth rate(SGR),daily feed intake(DFI),feed efficiency(FE) and protein efficiency ratio(PER) were unchanged in fish fed S0,S10 or S20,but were significantly lower in fish fed S30,S40,or S50(P0.05).The condition factor(CF) was lower and the digestive tract index(DTI) was higher in fish supplemented with alfalfa protein concentrate(P0.05).The apparent digesti-bility of dry matter,protein,and lipid were all linearly decreased by the addition of alfalfa protein concentrate(P0.05).Broken line analysis based on SGR revealed that the optimum replacement ratio was 19.0% in the diets of juvenile black sea bream,body weight(83.0±0.20) g.The levels of muscle lipid were significantly lower in fish fed S40 than those fed diets S0 and S20(P0.05),while there was no obvious effect on the other proximate con-stituents(P0.05).Liver moisture increased significantly in fish fed diets S0,S10,and S20,and then leveled off in fish fed diets S30,S40,and S50.The reverse was true for liver lipid content.Crude protein was significantly higher in the liver of fish fed diets S30 and S50 than in fish fed S0.Liver crude ash content was not affected by fishmeal replacement.The whole fish moisture content was increased whereas crude lipid content was decreased by dietary fishmeal substitution with alfalfa protein concentrate(P0.05).Whole fish crude protein content was highest in fish fed S30 and lowest in fish fed S40.There was no change in whole fish crude ash content(P0.05).Triglycerides were significantly reduced by replacement of 20% fishmeal.Cholesterol content and lysozyme(LSZ) activity were both linearly decreased by alfalfa protein concentrate supplementation(P0.05).Alkaline phosphate(ALP) activity was depressed by diets S20 to S50(P0.05).AST and ALT activities were enhanced by experimental diets with a replacement ratio of 20% and 40%,respectively.There was no difference in malondialdehyde(MDA) content in fish fed diets S10 to S50,which were lower than fish fed diet S0(P0.05).There was no relationship between superoxide dismutase(SOD) activity and the fishmeal replacement ratio.In summary,our results suggest that alfalfa protein concentrate can replace up to 19.0% fishmeal protein in the diets of juvenile starry flounder.