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). Maximum weight gain (WG), specific growth rate (SGR), feed efficiency ratio, protein efficiency ratio and protein productive value (PPV) occurred at 17.2 g methionine kg )1 diet, beyond which they showed declining tendency. Protein contents in whole fish body and dorsal muscle were positively correlated with dietary methionine level, while muscle lipid content was negatively correlated with it. Apparent digestibility coefficients (ADCs) of dietary nutrients were significantly affected by dietary treatments except for ADCs of crude lipid. Fish fed the grade level of methionine demonstrated a significant improvement in wholebody methionine content, total essential amino acids ( P EAA), total non-essential amino acids ( P NEAAs) and P EAA/ P NEAA ratio (P < 0.05). Regarding serum characteristics, significant differences were observed in total cholesterol, glucose and free methionine concentration (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. KEY WORDS

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The 8-week experiment was conducted to evaluate the effects of partial replacement of fish meal (FM) with soybean protein concentrate (SPC) on juvenile black sea bream, Acanthopagrus schlegelii (10.70 ± 0.04 g). Diets were formulated to replace FM protein by SPC at 0, 8, 16, 24, 32 or 40% (designated as T1, T2, T3, T4, T5 and T6, respectively). Diets except T1 were supplemented with phytase at 2000 phytase activity U kg )1 . The results showed that survival rate, growth performance and feed utilization were not significantly affected by increasing dietary SPC. Fish fed diet T3 had higher feed intake compared to those fed T1, T2 and T5 diets. Whole body compositions of black sea bream were significantly influenced by SPC replacing FM except for protein, ash and phosphorus content. Condition factor of fish was significantly lower in T2 than that of fish in T3 group. Apparent digestibility coefficients (ADCs) of dry matter was higher in fish fed T6 diet than those of fish fed T1 and T2 diets, ADCs of phosphorus increased with dietary SPC level up to T3 and then decreased. The results obtained in this study indicate that FM protein could be effectively replaced by SPC protein with phytase in diet of black sea bream. KEY WORDS