Growth, bone mineralization, and heat and low oxygen tolerance in European whitefish (Coregonus lavaretus L.) fed with graded levels of phosphorus

Trials were conducted to determine the dietary phosphorus (P) requirement of European whitefish, and to assess the effects of sub-optimal P feeding on growth, bone mineralization, lipid accumulation in the body and on heat and low-oxygen tolerance. Four replicate groups of whitefish fingerlings were fed in excess with one of five semipurified diets containing 4.4 to 14.9 g P kg(-1). The P requirement was estimated by nonlinear curve fitting to bone mineralization and growth rate data. Dietary P and energy availabilities were measured at the determined requirement level. Fish fed no P supplement showed typical hypophosphatemia in poorly mineralized bones, a low whole-body P content and a low plasma phosphate concentration. Hypophosphatemic fish grew slower and had elevated whole body lipid concentrations. To obtain 95% of the maximum vertebra ash concentration and maximum growth, respectively, 6.5- and 6.2-g available P kg(-1) diet was required. Fish fed low dietary P contents had higher whole body lipid levels than fish fed P at or above the determined requirement level. Hypophosphatemic fish had slightly, although statistically significant, lower upper lethal temperature than fish fed with adequate P contents (28.8 vs. 29.4 degreesC). Tolerance of low dissolved oxygen did not differ between fish fed low or high P contents (1.47 vs. 1.45 mg l(-1)) (C) 2002 Elsevier Science B.V. All rights reserved.