Effects of different dietary vitamin A levels on growth and serum biochemical parameters for Japanese seabass(Lateolabrax japonicus)

A 9-week feeding experiment was conducted to evaluate the effect of dietary vitamin A level on growth and serum biochemical parameters for juvenile Japanese seabass,Lateolabrax japonicus.Six groups of isonitrogenous(43% crude protein)and isoenergetic(20 kJ/g dry matter)purified diets(Diets 1-6)containing 245,1 005,1 835,3 781,7 583 and 15 273 IU vitamin A(supplied as retinyl acetate)per kg diet were fed twice daily to triplicate groups(10 fish/group)of fishinitial weight(10.20±0.14)g/fishin 120 L plastic tanks.Fish fed the basal diet(Diet 1)developed heavy mortality,exophthalmos,haemorrhages at the base of the fins and distortion of operculum.None of these deficiency signs were observed in fish fed the vitamin A supplemented diets(Diet 2-6).Carcass lipid content significantly increased with dietary increasing vitamin A level,while protein and moisture showed no significant differences.The analyses of serum parameters showed that the activity of alkaline phosphatase(AKP),the content of triacylglycerol(TG)and total cholesterol(TC)all significantly increased with the increase of dietary vitamin A level,while the activities of glutamate transaminase(ALT)and aspartate aminotransferase(AST)had the reverse trend.Broken-line regression analysis of weight gain or liver vitamin A content showed that juvenile Japanese seabass require a minimum of 1 934.8 IU vitamin A/kg diet for maximal growth or 3 546.6 IU vitamin A/kg diet for maximal liver vitamin A deposition.