Growth and tissue calcium and phosphorus deposition of juvenile discus fish (Symphysodon haraldi) fed with graded levels of calcium and phosphorus

Abstract

An 8-week feeding trial was conducted to investigate the effects of different levels of dietary calcium (Ca) and phosphorus (P) on growth performance and tissue Ca and P deposition of juvenile discus fish Symphysodon haraldi. Discus with an initial body weight of 4.98 ± 0.26 g were fed three times daily with one of the 12 experimental diets containing 0, 5, 10 and 15 g/kg of Ca cross with 0, 5 and 10 g/kg P. Levels of aqueous Ca and total P, temperature and pH were detected daily with mean values of 36.50 ± 0.48 mg/L, 1.42 ± 0.04 mg/L, 29.0 ± 0.5 °C and 7.8 ± 0.3, respectively. After 8-week feeding, it showed a remarkable decline on survival with dietary P (P < 0.05) but no such a difference with dietary Ca (P > 0.05). When P inclusion was 5 or 10 g/kg, the specific growth rate and protein efficiency ratio of discus were all reduced with Ca level (P < 0.05). Without dietary Ca, discus fed diet with 10 g/kg P obtained the best growth performance but which was not different from that with 5 g/kg P (P > 0.05). Dietary Ca and P had interactive effects on whole-body crude protein and ash (P < 0.05). Considering the individual element, P supplement significantly increased ash content but reduced lipid accumulation (P < 0.05). Dietary inclusion of Ca and P increased their concentrations in discus vertebra, scale and whole body but did not affect scale Ca/P ratio. Discus fed diet without Ca showed a higher Ca deposition rate than those with it and Ca deposition rate was elevated by dietary P. In the present aqueous Ca and P conditions, dietary inclusion of 5 g/kg P but with no Ca was beneficial for the growth and survival of juvenile S. haraldi.