Effect of dietary phosphorus and vitamin D-3 on phosphorus levels in effluent from the experimental culture of rainbow trout (Oncorhynchus mykiss)

Excessive phosphorus (P) levels in aquaculture effluents violate federally mandated limits and pose a serious threat to the freshwater environment. In rainbow trout culture, effluent P probably originates as fecal and metabol ic waste product because assimilation of dietary P is relatively low. We th erefore decreased dietary P and increased dietary vitamin D-3 levels, metho ds that enhance P assimilation in mammals, in purified and semi-purified tr out diets, then monitored effluent P. Soluble effluent P reached a peak rig ht after feeding and returned to baseline levels in between feeding times. The peak and average concentrations of soluble P in the effluent were mainl y influenced by dietary P. Average P in fecal dry matter also decreased wit h dietary P. Neither dietary P nor vitamin D, under the conditions of the e xperiment had significant effects on whole body P ceffluent indicating a st rategy whereby effluent P concentrations can be reduced by regulation of P metabolism content but P deposition (as a percentage of P intake) decreased with increased dietary P. The dietary combination of low P and high vitami n D-3 decreased soluble and fecal P levels in the (C) 2001 Elsevier Science BN. Ail rights reserved.