Quantitative methionine requirement of yellowtail (Seriola quinqueradiata)

The quantitative methionine requirement of juvenile yellowtail was determined by feeding diets containing six levels of L-methionine ranging from 0.57 to 1.58% of dry diet in about 0.2% increments. Duplicate tanks, each containing 20 fish, were assigned to each diet, The fish were fed to satiation four times a day for 30 days and weight gain, feed utilisation parameters, hepatosomatic index (HSI), body and liver compositions, and serum components were measured. Weight gain, feed efficiency, protein efficiency ratio, nitrogen retention and HSI increased with increasing levels of methionine up to 1.20% and remained nearly constant thereafter. Protein and fat contents of body and liver were significantly different between treatments. Fish fed the diet with the lowest methionine content gave poor haematological characteristics and serum components. Based on broken line analysis of percent weight gain and feed efficiency, the methionine requirement of juvenile yellowtail was estimated to be 1.11% of the diet or 2.56% of dietary protein in the presence of 0.31% cystine. (C) 1997 Elsevier Science B.V.