Dietary l-methionine requirement of juvenile black sea bream (Sparus macrocephalus) at a constant dietary cystine level

Abstract

An 8-week feeding trial was conducted to determine the effects of dietary methionine level on juvenile black sea bream Sparus macrocephalus. Fish (initial body weight: 14.21 ± 0.24 g) were reared in eighteen 350-L indoors flow-through circular fibreglass tanks (20 fish per tank). Isoenergetic and isonitrogenous diets contained six levels of L-methionine ranging from 7.5 to 23.5 g kg−1 of dry diet in 3.0 g kg−1 increments at a constant dietary cystine level of 3.1 g kg−1. Growth performance and feed utilization were significantly influenced by dietary methionine levels (P 0.05), while total protein level and triacylglycerol concentration kept relatively constant among treatments (P < 0.05). Analysis of dose response with second-order polynomial regression on the basis of either SGR or PPV, the optimum dietary methionine requirements of juvenile black sea bream were estimated to be 17.1 g kg−1 of diet (45.0 g kg−1 methionine of protein) and 17.2 g kg−1 of diet (45.3 g kg−1 methionine of protein) in the presence of 3.1 g kg−1 cystine, respectively.