Mineral balance and bone formation in fast-growing Atlantic salmon parr (Salmo salar) in response to dissolved metabolic carbon dioxide and restricted dietary phosphorus supply

Intensive production of smolts commonly results in reduced water quality (high CO2 and low pH) in tanks with restricted water supply, oxygenated water, and high fish density. In the present study, we investigated the effects of high and marginally low dietary phosphorus (P) content (within currently recommended dietary P range), of suboptimal water quality, and of interactions between these factors on whole body and vertebral mineral content and bone formation. After 30 days, there were no detectable effects on final body weight of any treatment. The parr fed the Low-P diet had significantly higher whole body content of lipid, and lower content of ash, P, Ca, Mg, and Zn than those fed the High-P diet. Similarly, the vertebrae contained less minerals and the Ca:P ratio was lower in fish fed the Low-P diet. Reduced water quality, on the other hand, caused higher content of whole body lipid and some minerals. In the present study, diets with P contents within the recommended range induced critical differences in whole body and vertebral mineral content. The effects caused by reduced water quality were of a lesser magnitude, and towards increased content of some minerals rather than a decrease. Also, there was no evidence that a sub-optimal water quality had an enhancing effect on the mineral imbalance caused by phosphorus deficiency.