Conversion of beta-carotene, canthaxanthin and astaxanthin to vitamin A in Atlantic halibut (Hippoglossus hippoglossus L.) juveniles

Larval Atlantic halibut fed Artemia has previously been shown to contain lower levels of Vitamin A compared to larvae fed zooplankton. The two types of live prey contain small or no amounts of vitamin A, but high levels of carotenoids that can be converted to vitamin A in other fish species. The purpose of this study was to investigate the ability of Atlantic halibut juveniles to convert beta-carotene, astaxanthin and canthaxanthin to vitamin A. Three levels of each carotenoid and retinyl acetate were fed to Atlantic halibut juveniles for 60 days. A vitamin A and carotenoid deficient diet was fed in triplicate as control. A HPLC method modified from Noll (1996) and validated for fish matrix was used to quantify both all-trans-retinol and 3,4-didehydro retinol. By comparing regression coefficients we observed that the increasing levels of carotenoids in the diets were reflected in increasing levels of vitamin A in both whole fish and liver samples. All carotenoids were converted to vitamin A, but to different degrees. Retinyl acetate and beta-carotene resulted in whole fish vitamin A levels significantly higher than canthaxanthin and astaxanthin. 3,4-didehydro retinol was not detected when the overall level of all-trans-retinol was low. When 3,4-didehydro retinol appeared, it was always in lower levels than all-trans-retinol.