Dietary valine requirement of juvenile blunt snout bream (Megalobrama amblycephalaYih, 1955)

Abstract

An 8-week feeding trial was carried out to test the hypothesis that adequate dietary valine might improve growth, feed utilization and protein content in blunt snout bream, whereas a valine deficiency might have adverse effects on these parameters. Six isonitrogenous (34% crude protein) and isoenergetic (14.2 MJ kg−1 digestible energy) experimental diets were formulated to contain graded valine levels (0.66, 0.95, 1.26, 1.55, 1.87 and 2.16% of dry weight) at about 0.30% increments replaced by equal proportions of glycine. At the end of the experiment the survival rate was not significantly affected by the dietary valine level. Final weight, weight gain (WG), specific growth rate (SGR), feed efficiency ratio (FER) and protein efficiency ratio (PER) increased with an increasing dietary valine level up to the 1.26% diet, and thereafter remained relatively constant. Dietary valine levels significantly affected the viscerosomatic index, but not the hepatosomatic index or condition factor. The dietary valine levels significantly affected the protein contents of whole body and plasma. Dietary valine supplementation significantly increased the plasma valine concentration, but not the levels of other branched-chain amino acids (isoleucine and leucine). Based on SGR and FER, the optimal dietary valine requirements of juvenile blunt snout bream were determined to be 1.32% of the diet (3.88% of dietary protein) and 1.26% of the diet (3.71% of dietary protein), respectively, using broken-line regression analysis.