The dietary valine requirement for rainbow trout, Oncorhynchus mykiss, can be estimated by plasma free valine and ammonia concentrations after dorsal aorta cannulation

This study was carried out to evaluate the dietary valine requirement by measuring means of the plasma free valine and ammonia concentrations in rainbow trout, Oncorhynchus mykiss, after dorsal aorta cannulation. A total of 35 fish averaging 498 +/- 7.2 g (initial body weight, mean +/- SD) were randomly distributed into seven groups with five fish in each group. After 48 h of feed deprivation, each group was fed one of seven L-amino acid based diets containing graded levels of valine (0.45, 0.95, 1.20, 1.45, 1.70, 1.95 or 2.45% of diet, dry matter basis) by intubation at 1% body weight. Blood samples were taken at 0, 5 and 24 h after intubation. Post-prandial plasma free valine concentrations (PPval, 5 h after intubation) and post-absorptive free valine concentrations (PAval, 24 h after intubation) of fish fed diets containing 1.45% or more valine were significantly higher than those of fish fed diets containing 1.20% or less valine (P < 0.05). Post-prandial plasma ammonia concentrations (PPA, 5 h after intubation) remained low or constant from fish fed diets containing 0.45-1.45% valine, but increased linearly from fish fed diets containing 1.45-2.45% valine. Post-absorptive plasma ammonia concentrations in the present study were not significantly different among the groups. Broken-line model analyses on PPval, PAval and PPA indicated that the dietary valine requirements of rainbow trout was between 1.41 (3.85) and 1.50% (4.10) of diet (% of dietary protein on a dry matter basis).