Methionine
requirement of juvenile Japanese flounder Paralichthys olivaceus
estimated by the oxidation of radioactive methionine
Growth and amino acid oxidation studies were
conducted to estimate methionine requirement of juvenile Japanese flounder, Paralichthys
olivaceus, by using the purified diets containing 500 g kg–1
crude protein from casein, gelatine and crystalline amino acids (CAA). Diets
with six graded levels of methionine (5.3, 8.3, 11.3, 14.3, 17.3 and 20.3 g kg–1
diet) were fed to triplicate groups of the juvenile (initial weight 2.8 ± 0.05 g)
twice a day for 40 days. To prevent leaching losses, CAA were precoated
using carboxymethylcellulose (CMC), and further diets were bound by CMC and
k-carrageenan. Based on broken-line analysis of percentage weight gain and
feed conversion efficiency, the methionine requirements of Japanese flounder
in the presence of 0.6 g kg–1 of cystine were 14.9
and 14.4 g kg–1 dry diet, respectively. After the
growth study was finished, a direct estimate of methionine requirement was
made by examining the influence of dietary methionine level on 14C-methionine
oxidation by determining radioactive carbon dioxide, protein and nonprotein
fractions of the whole body. The dose–response curve between expired
radioactive CO2 and dietary methionine levels showed that the
optimum methionine level for the flounder was estimated to be within the
range of 14.3–17.3 g kg–1 of diet in high agreement
with values obtained from the growth study.
(Laboratory of Aquatic Animal Nutrition, Faculty of
Fisheries, Kagoshima University, Shimoarata 4-50-20, Kagoshima 890-0056,
Japan. E-mail of S. Teshima: teshima@fish.kagoshima-u.ac.jp)