Essentiality of phosphorus, magnesium, iron, zinc, and manganese in milkfish diet

Abstract

Six semi-purified casein based diets were formulated to contain either a complete mineral mixture (control) or mineral premixes from which a specific test mineral was deleted to obtain phosphorus(P)-free, magnesium(Mg)-free, iron(Fe)-free, zinc(Zn)-free, or manganese(Mn)-free diets. These diets were fed to juvenile milkfish (mean initial weight 2.60±0.08g) for a 22-week experimental period. Final mean percent weight gain ranged from 1022 to 1379% with P-free (1022%) and Fe-free (1066%) diets obtaining a significantly lower weight gain (p<0.01) than the control diet (1270%). Survival was greater than 90% and did not differ significantly among treatments.

Upon termination of the growth experiment, milkfish flesh, bones, and combined samples of head, skin, and scales were dissected and analyzed for ash, P, Ca, Mg, Fe, Zn, and Mn content. The deletion of P or Fe from mineral mixture lowered P content in flesh and bone. Zn content in bone of fish was also lowered by exclusion of Zn, Mn, Mg or Fe. The result of this study demonstrated that it is necessary to supplement P and Fe even to semi-purified casein based diets.