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

Six semi-purified casein based diets were formulated to contain either a co mplete 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 wer e fed to juvenile milkfish (mean initial weight 2.60+/-0.08 g) for a 22-wee k experimental period. Final mean percent weight gain ranged from 1022 to 1 379% with P-free (1022%) and Fe-free (1066%) diets obtaining a significantl y 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 combi ned 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 mix ture lowered P content in flesh and bone. Zn content in bone of fish was al so lowered by exclusion of Zn, Mn, Mg or Fe. The result of this study demon strated that it is necessary to supplement P and Fe even to semi-purified c asein based diets.