Dietary arginine requirement of juvenile blunt snout bream, Megalobrama amblycephala

A 9-week feeding trial was conducted to quantify the dietary arginine requirement of juvenile blunt snout bream. Six isonitrogenous and isoenergetic semi-purified diets (34.0% crude protein) were formulated to contain graded arginine levels (0.83% to 3.36% of dry weight) at 0.5% increments replaced by equal proportions of glycine. At the end of the feeding trial, the results showed that survival rate was not significantly affected by dietary arginine level. Final weight, specific growth rate (SGR), feed efficiency ratio (FER), protein efficiency ratio (PER) and protein productive value (PPV) increased with increasing dietary arginine level from 0.83 to 1.81% (P < 0.05), thereafter showed a declining trend but the differences were not significant. Whole body compositions were independent of dietary arginine levels (P > 0.05). Plasma arginine concentration increased with the increase of dietary arginine from 0.83% to 1.81%, and thereafter was relatively constant, while lower lysine content in plasma was observed in fish fed the diet with 3.36% arginine level compared to those fed diets with 0.83-2.35% arginine (P < 0.05). Significantly higher plasma urea content was observed in fish fed diet with 3.36% arginine compared with those fed 0.83% arginine diet (0.83%). Significantly lower plasma total nitric oxide synthase (T-NOS) activities were observed in fish fed 0.83% arginine diet than those fed diets with 2.35-3.36% arginine. Plasma superoxide dismutase (SOD) activities and ammonia contents were not significantly affected by dietary arginine levels. Based on SGR, FER and PER, the optimal dietary arginine requirement of juvenile blunt snout bream was estimated to be 2.46% of the diet (7.23% of dietary protein), 2.28% (6.71% of dietary protein) and 2.26% of the diet (6.65% of dietary protein), respectively.