| Summary: | Abstract This study evaluated the dietary lysine requirement by measuring the plasma free lysine concentrations in rainbow trout, Oncorhynchus mykiss after dorsal aorta cannulation. A basal diet containing 36.6 % crude protein (29.6 % crystalline amino acids mixture, 5 % casein and 2 % gelatin) was formulated to one of the seven L-amino acid based diets containing graded levels of lysine (0.72, 1.12, 1.52, 1.92, 2.32, 2.72 or 3.52 % dry diet). A total of 35 fish averaging 512 ± 6.8 g (mean ± SD) were randomly distributed into seven groups with five fish in each group. After 48 h of feed deprivation, each group of fish was fed one of the experimental diets by intubation at 1 % body weight. Blood samples were taken at 0, 5 and 24 h after intubation. Post-prandial plasma free lysine concentrations (PPlys, 5 h after intubation) of fish fed diets containing ≥ 2.32 % lysine were higher than those of fish fed diets containing ≤ 1.92 % lysine. Post-absorptive free lysine concentrations (PAlys, 24 h after intubation) of fish fed diets containing 2.32 and 3.52 % lysine were higher than those of fish fed diets containing ≤ 1.52 % lysine. The broken-line regression analysis on the basis of PPlys and PAlys indicated that the lysine requirement of rainbow trout could be 2.34 and 2.20 % in diet. Therefore, these results strongly suggested that the dietary lysine requirement based on the broken-line model analyses of PPlys and PAlys could be greater than 2.2 but less than 2.34 % (corresponding to be 6.01 % ≤, but ≤ 6.39 % in dietary protein basis, respectively) in rainbow trout. Also, these results shown that the quantitative estimation of lysine requirement by using PPlys and PAlys could be an acceptable method in fish.
|
|---|