Growth performance, digestive enzyme, transaminase and GH-IGF-I axis gene responsiveness to different dietary protein levels in broodstock allogenogynetic gibel carp (Carassius auratus gibelio) CAS III

Abstract

A 60-day growth trial was conducted to investigate the effect of dietary protein levels on growth performance, digestive enzyme activities, transaminase activities and GH-IGF-I axis gene expression of broodstock gibel carp (initial body weight, 180.3 +/- 0.4 g) using diets containing white fishmeal and casein as the main protein sources. Six isolipidic (100 g kg(-1)) and isoenergetic (gross energy 17.5 kJ g(-1)) diets were prepared, with protein levels ranging from 200 to 400 g kg(-1) at 40 g kg(-1) increments. Each diet was fed by hand to triplicate groups of 22 fish each to apparent satiation four times a day. Results indicated that specific growth rate (SGR), feed efficiency (FE) and protein retention efficiency (PRE) significantly increased with the increase of dietary protein levels from 200 to 360 g kg(-1), after that, SGR and FE plateaued while PRE notably decreased. Whole-body and muscle crude lipid increased and moisture decreased with increasing dietary protein levels; whereas crude protein and ash in whole-body and muscle, condition factor, vicerosomatic index and hepatosomatic index showed no obvious differences between treatments. Plasma ammonia concentration, hepatic alanine transaminase and aspartate transaminase activities markedly enhanced with the increase of dietary protein level up to 320-360 g kg(-1). Intestinal trypsin activity peaked in fish fed protein level of 320 g kg(-1), and then remarkably descended; while no significant differences were observed in intestinal lipase and alpha-amylase. The relative mRNA abundance of insulin like growth factor-I (IGF-I) in liver notably up-regulated with dietary protein level increasing to 360 g kg(-1), and down-regulated at higher protein level. Pituitary growth hormone (GH) mRNA showed an almost opposite trend with IGF-I. In conclusion, based on a broken-line analysis of SGR, the recommended dietary protein level for broodstock gibel carp was 369 g kg(-1), which was higher than that for sub-adult fish.