Elevated Water CO 2 Can Prevent Dietary-Induced Osteomalacia in Post-Smolt Atlantic Salmon ( Salmo salar , L.).

Expansion of land-based systems in fish farms elevate the content of metabolic carbon dioxide (CO 2 ) in the water. High CO 2 is suggested to increase the bone mineral content in Atlantic salmon ( Salmo salar , L.). Conversely, low dietary phosphorus (P) halts bone mineralization. This study examines if high CO 2 can counteract reduced bone mineralization imposed by low dietary P intake. Atlantic salmon post-seawater transfer (initial weight 207.03 g) were fed diets containing 6.3 g/kg (0.5P), 9.0 g/kg (1P), or 26.8 g/kg (3P) total P for 13 weeks. Atlantic salmon from all dietary P groups were reared in seawater which was not injected with CO 2 and contained a regular CO 2 level (5 mg/L) or in seawater with injected CO 2 thus raising the level to 20 mg/L. Atlantic salmon were analyzed for blood chemistry, bone mineral content, vertebral centra deformities, mechanical properties, bone matrix alterations, expression of bone mineralization, and P metabolism-related genes. High CO 2 and high P reduced Atlantic salmon growth and feed intake. High CO 2 increased bone mineralization when dietary P was low. Atlantic salmon fed with a low P diet downregulated the fgf23 expression in bone cells indicating an increased renal phosphate reabsorption. The current results suggest that reduced dietary P could be sufficient to maintain bone mineralization under conditions of elevated CO 2 . This opens up a possibility for lowering the dietary P content under certain farming conditions.