Sulphur amino acid requirement of juvenile Asian sea bass Lates calcarifer

The dietary requirement of juvenile Asian sea bass Lates calcarifer Bloch for total sulphur amino acids was studied. Fish (average initial weight of 2.59 +/- 0.08 g) were reared in twelve 500 L fibreglass tanks provided with flow-through seawater at 26 degrees C and salinity of 31 p.p.t. for 12 weeks. They were fed semipurified test diets containing 6.2, 7.2, 8.1, 9.0, 10.8, or 12.6 g methionine kg-l dry diet and a basal level of 3.1 g cystine kg(-1) dry diet. The mean crude protein of the diets (containing defatted Peruvian fishmeal, squid meal, soybean meal, and free amino acid mixture to simulate the pattern of hydrolysed sea bass protein) was 46.02%. The crude fat content of the diets was 10.51% from a 1:1 mixture of cod liver oil and soybean oil. Survival was 100% in all treatments. On the basis of the growth response, the total sulphur amino acid requirement of juvenile Asian sea bass was estimated to be 13.4 g kg(-1) dry diet (2.9% of protein). Fish fed low levels of L-methionine had significantly lower weight gains and feed efficiency ratios as well as slightly higher hepatosomatic indices. No nutritional deficiency signs were observed other than growth depression in fish fed on diets that were low in methionine. This information is valuable in further refinement of formulations of practical diets for the Asian sea bass.