Phosphorus requirements of gilthead sea bream (Sparus aurata L.) juveniles

A trial was conducted to evaluate the phosphorus requirements of gilthead sea bream juveniles. Seven semipurified diets were formulated to contain 54% crude protein and 15% lipids and phosphorus (dicalcium phosphate) levels ranging from 0.37% to 1.5% (DM basis). Each diet was fed to duplicate groups of 25 fish with an initial average weight of 5 g over 42 days. The fish were fed by hand to visual apparent satiety twice daily, six days a week. At the end of the trial growth rate was not significantly different in groups fed diets containing 0.75% phosphorus or higher, while growth rate of fish fed the 0.37% phosphorus diet was significantly lower than all the other diets. Feed efficiency ratio, protein efficiency ratio and N retention were significantly lower in fish fed the 0.37% phosphorus diet than in those fed diets with 0.75% and higher phosphorus levels. Phosphorus content of the fish averaged 2% (on a dry weight basis) and was not significantly affected by dietary phosphorus content. Phosphorus retention averaged 6.6 g kg(-1) weight gain and was not statistically different among groups. Phosphorus retention (% phosphorus intake) decreased with the increase of dietary phosphorus content, being even higher than 100% in groups fed diets with 0.37% and 0.57% phosphorus, indicating phosphorus absorption from the water, The results of this study indicate that phosphorus requirements of gilthead sea bream juveniles were satisfied with a diet including 0.75% phosphorus.