EFFECTS OF DIETARY PROTEIN AND LIPID LEVELS ON GROWTH, FEED UTILIZATION AND BODY COMPOSITION OF CYPRINUS LONGIPECTORALIS

Abstract

Cyprinus longipectoralis,also known as the spring carp,is a native fish with high economic and ecological value in the Erhai Lake,Yunnan Province,China.Since the 1970’,this fish species seldom appeared in the catch of Erhai Lake,because of overfishing and some other ecological reasons.In recent years,spring carps were recruited through artificial breeding and stock enhancement.However,during the artificial breeding process,farmers could not find a suitable commercial feed because little was known about the nutrient requirements of this species.As two main dietary nutrients,protein and lipid play a key role in fish growth and development.Therefore,this study was designed to investigate the effects of dietary protein and lipid levels on the growth,feed utilization and body composition of juvenile spring carps and the dietary protein and lipid requirements of this fish with initial body weight of 0.55 g,based on the broken-line method.The experimental diets were formulated based on casein,wheat middling,fish oil,corn oil and corn starch.This study adopted a factorial design of 3(protein level) × 3(lipid level) and the nine isocarlorie(17.8 kJ/g) diets contained the protein concentrations of 33%,39% or 45% and the lipid concentrations of 5%,8% or 11%,respectively.One of the nine experimental diets was fed to 30 fish in each tank(67 cm × 46 cm × 50 cm,with a water volume of 130 L) in triplicate for 56 days.During the experiment,the fish were fed by hand to satiation twice daily in an indoor flow system at(28±2)℃,and unconsumed feeds were siphoned 1h after feeding,dried and weighed.The results showed that there were no significant effects of dietary protein and lipid levels on growth,feed utilization and body composition except whole body moisture content(P0.05).Feeding rate decreased significantly while feed efficiency,energy retention efficiency,whole body protein and moisture content significantly increased with the increasing crude protein concentrations(P0.05).Specific growth rate,protein efficiency ratio,protein retention efficiency,and whole body ash content were not significantly affected by dietary crude protein concentrations(P0.05).Whole body lipid content significantly increased while specific growth rate,protein retention efficiency and whole body protein content significantly decreased with the increasing crude lipid concentrations(P0.05).However,feeding rate,feed efficiency,energy retention efficiency and whole body ash content were not significantly affected by dietary crude lipid levels(P0.05).Broken-line analysis based on specific growth rate showed that the optimum dietary protein/lipid ratio of juvenile spring carps was 7.30.We concluded that 33%—34% dietary crude protein level and 4%—5% lipid level were optimal for juvenile Cyprinus longipectoralis.