Influence of low dietary cholecalciferol intake on phosphorus and trace element metabolism by rainbow trout (Oncorhynchus mykiss, Walbaum)

A study was conducted to investigate the relationship between dietary chole calciferol and phosphorus (P) metabolism in rainbow trout (Oncorhynchus myk iss). Triplicate groups of rainbow trout fingerlings, initial weight 12.4 /- 0.7 g, were fed to satiation one of four semipurified diets containing e ither 3.2 or 5.6 g kg(-1) P and either 100 or 2600 IU kg(-1) cholecalcifero l in a 2 x 2 factorial design. The fish were reared in freshwater for 20 we eks on a 12 h photoperiod regime without exposure to UV-radiation. Growth a nd feed efficiency of fish were not influenced by dietary cholecalciferol a nd P levels. Fish fed the diet containing 3.2 g P kg(-1) exhibited poor bon e mineralization, low plasma phosphate level and reduced carcass P concentr ation. The low level of dietary vitamin D-3 (100 IU kg(-1)) significantly i mproved bone mineralization. Liver cholecalciferol concentration was higher (4.9 vs 9 ng g(-1)) at 2600 IU kg(-1) cholecalciferol but dietary P had no effect on the liver content of this vitamin. Higher dietary P significantl y increased urine P concentration whereas dietary cholecalciferol level had no effect. Dietary P supplementation increased body ash, Ca and P but Mg a nd Mn levels decreased significantly. Although cholecalciferol supplementat ion increased Mn deposition, carcass Zn content decreased. While tripling i n weight during the trial, rainbow trout reared in freshwater effectively u tilized phosphorus from a low-cholecalciferol diet. (C) 1999 Elsevier Scien ce Inc. All rights reserved.