Effect of dietary calcium and phosphorus on growth, feed efficiency, mineral content and body composition of juvenile grouper, Epinephelus coioides

A study was conducted to investigate the effects of dietary calcium (Ca) and phosphorus (P) on juvenile grouper, and to characterize P deficiency signs. Six isoenergetic and isonitrogenous diets with two P levels (with or without P supplement) were prepared using casein and gelatin as the main protein sources. Juvenile grouper with an initial weight of 29.8 ± 0.15 g were fed to satiation with one of the six diets for 10 weeks. Fish fed diets without P supplement showed reduced growth, poor feed efficiency, loss of appetite, reduced ash content and mineral (Ca, P and Mg) deposition in scales, vertebrae and opercula, and an increase in body lipid content. When P was not supplemented, Ca supplement of 6 g kg^{- 1} had no significant effect on growth, ash content in scales, vertebrae and opercula, or mineral (Ca, P, Mg and Zn) deposition in scales and vertebrae, but increased feed efficiency, and Ca and P depositions in opercula, and lowered protein level in liver. When diets were supplemented with 6 g kg^{- 1} P, Ca supplement of 6 g kg^{- 1} had no significant effect on growth, or the ash and mineral (Ca, P and Mg) content in scales, vertebrae and opercula, but excess Ca supplement (up to 12 g kg^{- 1}) had a negative effect on scale ash, mineral (Ca, P and Mg) deposition and vertebrae Zn deposition. Second-degree polynomial regression analysis has revealed a slight trend towards reduced growth at the high Ca levels. Interestingly, dietary Ca supplement also increased feed efficiency at the level of 6 g kg^{- 1} supplemental P. If feed efficiency and scale mineralization are taken into account, Ca supplement of 6 g kg^{- 1} (Ca / P = 1) might be optimum when diet was supplemented with 6 g kg^{- 1} P.