| Phosphorus is an essential micronutrient for aquatic animals. This study aims to research the effect of different levels of dietary phosphorus on growth, body proximate composition, tissue phosphorus content and its biochemical indexes of black seabream (Sparus macrocephalus). Based on bone phosphorus content, the optimal total phosphorus requirement are also determined.The black seabream juveniles were randomly allotted to six groups. Each replicate was composed of 25 fish with an mean weight of 11.45 ±0.02g. One group was fed the basal diet, which contained 0.49% total phosphorus, other five groups were fed experimental diets with 0.71%, 0.90%, 1.12%, 1.32% and 1.59% total phosphorus, respectively. After 8 weeks of feeding, fish were killed to collect the carcass, liver, muscle, scales, skin, vertebra, and plasma samples, then the body proximate composition, phosphorus content and biochemical parameters were analyzed.The growth trial suggested that the supplementation of dietary phosphorus could improve the growth of black seabream. Weight gain ratio (WGR), special growth rate(SGR), feed efficiency (FE) and,protein conversion efficiency (PCR) of fish were improved by the elevation of dietary phosphorus level and reached maximal value at 1.32% total phosphorus. No significant (P > 0.05) changes exist in condition factor of black seabream fed different levels of phosphorus, but the HSI (hepatosomatic index) was significantly improved with the increasing supplementation of dietary phosphorus. Phosphorus utilization efficiency and phosphorus retention coefficient attained optimal levels at 0.89% and 1.26% total dietary phosphorus by analysis, respectively.Supplementation of dietary phosphorus had no significant effect on the muscle moisture, muscle protein, lipids and the carcass moisture, but there was some effect on the carcass lipids and protein content, the carcass lipids content decreased with the increase of dietary phosphorus and no evident correlation between dietary phosphorus and carcass protein. Liver moisture, protein and lipids content were significantly influenced by dietary phosphorus: the first two indexes were positive with the supplementation but the latter was negative.There were positive correlations between ash, calcium and phosphorus content in carcass, skin, vertebra, scale of black seabream juveniles and dietary phosphorus. Among these indexes, phosphorus content in skin was the most sensitive to the dietary phosphorus. As well, the ash content in liver increased with elevation of dietary phosphorus content, but no significant changes were found in the muscle ash, phosphorus and calcium content(P>0.05). Dietary phosphorus and calcium/phosphorus ratio cannot exert significant influences on the calcium/phosphorus ratio in scales and vetebra, but the ratio in skin is affected to some extent.Dietary phosphorus supplementation had some influence on triglycerides (TG), cholesterol (CHO), lysozyme (LSZ), alkaline phosphatase (AKP) and creatine phosphoransferase (CK). With the elevation of dietary phosphorus, plasma CHO and TG content and liver CK activity decreased and reached the bottom at the total phosphorus levels of 1.12%, and then increased with further adding phosphorus. Muscle and plasma CK decreased while plasma LSZ activity increased with the phosphorus supplementation. Plasma AKP activity reduced to the lowest at 1.32%total phosphorus, and then increased with the further adding of dietary phosphorus. No significant correlation was found between liver AKP activity and dietary phosphorus levels.Based on ash content in vertebra of black seabream juveniles as the evaluating index, we can conclude that when the water temperature is 28 + TC, the optimal requirement of dietary phosphorus for black seabream juveniles of an initial mean weigh of 11.45g, is 1.39% orl3.9g per kilogram dry diet.
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