Methionine requirement of juvenile Japanese flounder Paralichthys olivaceus

Growth studies were conducted to determine the dietary methionine requireme nt of juvenile Japanese flounder Paralichthys olivaceus. A basal diet was f ormulated to contain 50% crude protein from casein and gelatin, as intact p rotein sources, supplemented with crystalline L-amino acids (CAA), to corre spond to the amino acid pattern found in the whole body protein of the juve nile Japanese flounder, except methionine. Test diets contained six graded levels of L-methionine 0.53, 0.83, 1.13, 1.43, 1.73, and 2.03% of diet (dry matter basis) or 1.06, 1.66, 2.26, 2.86, 3.46 and 4.06% of protein. To pre vent leaching losses of water-soluble amino acids, CAA were pre-coated with carboxymethylcellulose (CMC), and diets were further bound with both CMC a nd K-carrageenan after addition of the pre-coated CAA. Weighing about 2.80 g, each triplicate group of the juvenile flounder were fed test diets twice a day (5% of body weight) for 40 d. Survival rate, specific growth rate, f eed conversion efficiency and apparent protein retention were significantly (P < 0.05) affected by dietary methionine concentrations. The optimum diet ary level of methionine in the presence of 0.06% of dietary cystine for Jap anese flounder juvenile was estimated by using break point analysis. The va lues determined based on weight gain and feed efficiency were 1.49% of diet (or 2.98% of protein) and 1.44% of diet (or 2.88% of protein), respectivel y. These requirement values are close to the methionine level of flounder w hole body protein.