Effects of different dietary protein, lipid and digestible energy levels on growth and body composition of juvenile channel catfish(Ictalurus punctatus)

Abstract

A 60-day feeding trial including diets with two protein levels(22%,28%),two lipid levels(10.0%,14.0%)and two digestible energy levels(12.56 kJ/g,14.23 kJ/g)designed with three replications was conducted to investigate the growth,nutrient utilization and body composition of juvenile channel catfish.Four hundred and eighty fish(initial weight,141.5±1.0 g)were randomly distributed into 24 tanks(3.0 m×0.8 m×0.8 m)at a rate of 20 fish per tank and fed three times daily.Fish were fed respectively to apparent satiation by experimental diets named P28L10E14.23,P28L14E14.23,P22L10E14.23,P22L14E14.23,P28L10E12.56,P28L14E12.56,P22L10E12.56 and P22L14E12.56.Final weight,weight gain,specific growth rates(SGR)and feed conversion ratio(FCR)were not significantly affected by dietary protein or dietary lipid or dietary digestible energy(P0.05),but were significantly affected by a dietary protein×lipid interaction(P0.05),and extremely significantly affected by a dietary protein×lipid×digestible energy interaction(P0.01).With the protein/energy ratio increasing,it took an increasing trend to final weight,weight gain and SGR(P0.05),except that fish fed diet P28L10E12.56.The digestibility of dietary protein,lipid,energy and dry matter is increasing when dietary digestible energy decreased(P0.05)and dietary lipid increased(P0.05).With the dietary protein decreasing,it took a decreasing trend to the digestibility of dietary protein,energy and dry matter(P0.05).The digestibility of dietary protein,lipid,energy and dry matter is increasing by dietary lipid levels(P0.05).Nitrogen retention was significantly increased as dietary protein levels decreased(P0.05),lipid retention decreased significantly with dietary digestible energy and lipid levels decreasing(P0.05),protein efficiency ratio(PER)was significantly increased as dietary digestible energy decreased(P0.05).Carcass protein and lipid were not significantly affected by dietary digestible energy concentrations(P0.05);however,carcass lipid tended to improve(P=0.066)as dietary digestible energy levels increased.The results of this study indicated that the diet containing 28% protein with 14% lipid and 12.56 kJ/g digestible energy is optimal for growth of juvenile channel catfish(150 to 300 g weight).However,group P28L10E14.23 and P22L10E12.56 got second best weight,highest nutrient utilization and best body composition of juvenile channel catfish.It also indicates that lipid saved protein in diet of juvenile channel catfish.