Influence of low dietary cholecalciferol intake on phosphorus and trace element metabolism by rainbow trout (Oncorhynchus mykiss, Walbaum)
1999
Vielma, J. | Lall, S.P. | Koskela, J. | Mattila, P.
A study was conducted to investigate the relationship between dietary cholecalciferol and phosphorus (P) metabolism in rainbow trout (Oncorhynchus mykiss). Triplicate groups of rainbow trout fingerlings, initial weight 12.4 +/- 0.7 g, were fed to satiation one of four semipurified diets containing either 3.2 or 5.6 g kg(-1) P and either 100 or 2600 IU kg(-1) cholecalciferol in a 2 x 2 factorial design. The fish were reared in freshwater for 20 weeks on a 12 h photoperiod regime without exposure to UV-radiation. Growth and feed efficiency of fish were not influenced by dietary cholecalciferol and P levels. Fish fed the diet containing 3.2 g P kg(-1) exhibited poor bone mineralization, low plasma phosphate level and reduced carcass P concentration. The low level of dietary vitamin D3 (100 IU kg(-1)) significantly improved 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 significantly increased urine P concentration whereas dietary cholecalciferol level had no effect. Dietary P supplementation increased body ash, Ca and P but Mg and Mn levels decreased significantly. Although cholecalciferol supplementation increased Mn deposition, carcass Zn content decreased. While tripling in weight during the trial, rainbow trout reared in freshwater effectively utilized phosphorus from a low-cholecalciferol diet.
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