Interactions of phosphorus levels and abiotic factors for the occurence of vertebral deformities

Phosphorus is considered the main nutritional risk factor for skeletal deformities in Atlantic salmon. To avoid deformities, industry is pushing its limits for phosphorus inclusion levels in fish diets. Phosphorus is a limited and expensive resource, and aquaculture competes with agriculture for its inclusion in diets. Moreover, oversupply of phosphorus in diets results in water pollution, eventually leads to anoxic zones in water that lead to fish deprived of oxygen, and eventually dies. However, our previous trials at Skretting ARC have demonstrated that the phosphorus deficient or surplus diets did not induce/promote any vertebral deformities in Atlantic salmon (Witten et al., 2016). Further trial showed that phosphorus deficiency is reversible and fish bones can be re-mineralized without tissue alterations (Witten et al., 2018). Fish lives in water and water parameters (CO2, temperature, pH, etc.) are difficult to control and often times go above limits in common farming conditions that may result in reduced fish welfare. To replicate true farming conditions, we would like to test in a systematic manner the inclusion of different phosphorus levels in feed at normal and higher CO2 levels in water in 1200 farmed Atlantic salmon (S. salar). This will enable us to test the effects of water parameters in relation to phosphorus levels on the occurrence of vertebral deformities in Atlantic salmon. Additionally, appropriate phosphorus inclusion levels and their potential effects will be determined. Due to the unknown aetiology of deformities in salmonid aquaculture live animals must be used, however, the number used in the experiment is limited to that which will provide significant differences between control and experimental groups (assuming an alpha value of 0,05 and a power of 0,8).