Dietary phosphorus requirement of juvenile Japanese seabass, Lateolabrax japonicus

A feeding trial was conducted to estimate the optimum requirement of dietary available phosphorus for juvenile Japanese seabass in floating sea cages (1.5 × 1.5 × 2 m). Five practical diets were formulated to contain graded levels (0.31%, 0.56%, 0.70%, 0.93% and 1.17%) of available phosphorus from dietary ingredients and monocalcium phosphate (MCP). Each diet was randomly assigned to triplicate groups of fish, and each group was stocked with 60 fish (initial body weight, 6.28 ± 0.1 g). Fish were fed twice daily (06:30 and 16:30) to satiation for 8 weeks. During the experimental period, the water temperature fluctuated from 26.5 to 32.5 °C, salinity from 32‰ to 36‰ and dissolved oxygen was approximately 7 mg l^{- 1}. Specific growth rate (SGR) significantly increased with increasing available phosphorus from 0.31% to 0.70% of diet (P < 0.05), and then leveled off. The body composition analysis showed that the carcass ash, lipid and protein, as well as phosphorus contents in the whole body, vertebrae and scales, were significantly affected by dietary available phosphorus (P < 0.05). The blood biochemistry analysis showed that plasma phosphorus and plasma alkaline phosphatase (ALP) activity increased with the increase of dietary available phosphorus levels (P < 0.05). Broken-line analysis based on SGR indicated that the minimum available phosphorus requirement for the optimal growth of juvenile Japanese seabass was 0.68%. Based on the phosphorus content either in whole body or vertebrae, the requirements were 0.86% and 0.90%, respectively.