Phosphorus utilization by Atlantic salmon (Salmo salar) reared in freshwater is not influenced by higher dietary calcium intake
1998
Vielma, J. | Lall, S.P.
To decrease the phosphorus (P) load of fish farms, factors affecting dietary P utilization need to be known in more detail. A study was conducted to examine the effect of dietary calcium (Ca) level on dietary P utilization of Atlantic salmon reared in freshwater. Salmon fingerlings (initial weight 42.1 g) were fed a semi-purified diet (1.3 g kg-1 Ca, 3.1 g kg-1 P) with or without Ca and P supplement for 15 weeks. Fish fed no P supplement showed bone deformities and low Ca and P content of vertebrae. An increase in supplementary Ca level from 0 to 1.5% (increase in Ca:P ratio from 0.2 to 2.1) had no significant effect on bone mineralization when dietary P content was at the requirement level of Atlantic salmon. Plasma phosphate concentration in fish fed diets supplemented with 5 g P kg-1 was decreased by dietary Ca supplementation of 15 g kg-1. An increase in supplementary Ca from 0 to 0.75% had a positive effect on bone mineralization when dietary P content was below the requirement level. Correlation between scale and bone mineralization was significant. Magnesium level in plasma and deposition in calcified tissue decreased with increasing dietary Ca and P levels. Hepatic cholecalciferol (vitamin D3) content was 58.5 ng g-1 in fish fed without Ca or P supplements, and 9-10 ng g-1 in fish fed with either Ca or P supplements indicating its involvement in the regulation of Ca and P homeostasis. The results suggest that in commercial salmonid diets, a high Ca:P ratio is unlikely to interfere with dietary P utilization. However, the possibility of improving the performance of plant protein based diets of low Ca:P ratio by Ca supplementation exits.
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