Vitamin D requirement of juvenile channel catfish reared in calcium-free water

Typescript (photocopy).Two experiments were conducted with juvenile channel catfish reared in calcium-free well-water. The first experiment was designed to evaluate four vitamin D-deficient diets and graded levels of vitamin D₂ or D₃ within the range reported as optimum. The second experiment was designed to evaluate dietary hypervitaminosis D₃. Requirement estimates were 250 or 1000-2000 IU/kg of diet, depending on the criteria used to determine the minimum dietary level. Because this range is similar to previous estimates using fish reared in calcium-replete water, the lack of environmental calcium apparently does not influence the dietary vitamin D requirement. Vitamins D₂ and D₃ were equally efficacious in promoting weight gain of fish when fed at levels up to 1500 IU/kg of diet, but vitamin D₂ depressed weight gain when fed at 2000 and 2500 IU/kg of diet. Serum vitamin D metabolite samples had similar liquid chromatographic retention times to standards of vitamin D₃ origin, except for 25-hydroxyvitamin D from vitamin D₂-fed fish. The metabolite appeared to be 25-hydroxyvitamin D₂. There were no apparent toxic effects of feeding up to 1x10⁶ IU/kg of diet as vitamin D₃ for a period of fourteen weeks. Serum potassium concentrations were significantly higher in fish fed between 1000 and 2000 IU/kg of diet compared to fish fed higher or lower levels of either form of the vitamin. Calcium and phosphorus concentrations of serum and bone were not affected by feeding graded levels of vitamin D in calcium-free water