Establishing an upper level of intake for vitamin A in Atlantic salmon (Salmo salar L.) postsmolts

The vitamin A (VA) concentration in salmon aquaculture feeds is varying and may lead to sublethal adverse effects. In this study, 135g Atlantic salmon postsmolts were given eight diets in duplicates with 6, 12, 26, 55, 82, 112, 360 and 749mg retinol (ROL)kg(-1) for 116days. Subsequently, fish given 6, 82 and 749mg ROL kg(-1) were transferred to a common net pen and given a standard commercial diet for further 28weeks. Feed conversion rate, liver functionality and markers of VA homoeostasis were not negatively affected by dietary VA level, but chronic high VA intakes led to adverse effects on growth and bone health. In plasma, there was an antagonistic effect of dietary ROL on circulating 1,25 (OH)(2) vitamin D-3 (calcitriol). Moreover, a dose-response of VA on craniofacial deformities, condition factor and vertebral morphometry and mechanical strength was observed. Vertebral deformities were observed after 28weeks on a standard diet and not immediately after the 116days on the experimental diet. Elevated VA is a risk factor for bone deformities, and the dietary intake of VA should not exceed 37mg ROLkg(-1) body weight day(-1) in Atlantic salmon postsmolts.