Compensatory growth after various levels of dietary protein restriction in rainbow trout, Oncorhynchus mykiss

Abstract

This study was conducted to determine the effects of various levels of dietary protein restriction for 3weeks (phase 1) on compensatory growth, nutrient utilization, body compositions and organ indices of rainbow trout (Oncorhynchus mykiss) during a nine-week realimentation phase (phase 2). Five experimental treatments consisted of four protein restricted diets including 15, 22.5, 30 and 37.5% protein (RP15, RP22.5, RP30 and RP37.5 respectively) and the control diet 45% (C45). All diets were prepared to be isoenergetic at levels of 22.5MJkg−1 gross or 16.3MJkg−1 digestible energy. Each of five treatment groups was tried in triplicate groups of 75 fish with an average initial weight of 62.06±0.38g. Protein restriction in phase 1 linearly decreased specific growth rates of weight and length (SGRW and SGRL), body weight and length as well as feed utilization. The restriction induced a linearly increasing trend in protein retention efficiency, feed intake, organ indices such as viscera, pyloric caecum and hepato-somatic, whole body lipid and lipid/lean body mass whereas it induced a decrease in whole body moisture and protein at the end of phase 1. Protein restriction, except RP37, caused a significant increase in SGRW during phase 2 compared with C45, being most pronounced in the first 3weeks. Repeated measures ANOVA revealed a convergence in trajectories of ln body weight and length at the end of the experiment, suggesting that a complete catch up occurred in body mass and structure. There was also replenishment in distorted organ indices and body compositions, except protein which was still less in R15 than C45. More efficient utilization of feed and dietary protein by previously protein restricted fish during phase 2 appears to be the reason of the compensatory growth. At the end of the experiment, protein restriction was found to be effective in reduction of N loss.