RESPONSE TO CAROTENOIDS BY RAINBOW-TROUT IN THE SEA - RESORPTION AND METABOLISM OF DIETARY ASTAXANTHIN AND CANTHAXANTHIN

Rainbow trout (Oncorhynchus mykiss), with an average initial weight of 460 g, were fed diets containing 25, 50 and 100 mg/kg of racemic astaxanthin (1:2:1 mixture of the three optical isomers (3R,3′ R), (3R,3′ S), (3S, 3′ S)), and canthaxanthin, respectively, in comparison with a carotenoidfree control diet. The trout showed an average body weight increase of 450 g during the 16 weeks of feeding in sea pens. There was a tendency for astaxanthin to be more efficiently utilized than canthaxanthin for flesh pigmentation, and a final maximum concentration of 11 mg/kg was obtained when the highest dietary concentration of astaxanthin was fed. The benefit of increasing the dietary carotenoid concentration from 50 to 100 mg/kg was minimal compared with the increase from 25 to 50 mg/kg. The dietary carotenoids were deposited unchanged in the flesh. The trout fed canthaxanthin tended to accumulate more carotenoids in the skin as metabolites. In the skin of the astaxanthin-fed trout, astaxanthin esters predominated with a slight preference for the (3R,3′ S,meso) and (3S,3′ S) isomers relative to the (3R,3′ R) isomer. © 1990.