RESPONSE OF SERUM CAROTENOID LEVELS TO DIETARY ASTAXANTHIN AND CANTHAXANTHIN IN IMMATURE RAINBOW-TROUT ONCORHYNCHUS-MYKISS

Rainbow trout were fed a diet supplemented with astaxanthin (89 mg/kg) or canthaxanthin (116 mg/kg)in two different experiments: experiment 1 was designed to measure the kinetics of the appearance and disappear ance of carotenoids in the serum; experiment 2 was undertaken to estab lish the serum dose-response to synthetic astaxanthin and canthaxanthi n for immature rainbow trout. The serum carotenoid concentrations of i mmature rainbow trout increased when fish were fed carotenoid suppleme nted feed and then reached a plateau after 1 day of intake for astaxan thin and after 2 days for canthaxanthin. Circulating astaxanthin repre sented a value 2.3 times that of canthaxanthin. After dietary suppleme ntation was discontinued, the serum carotenoid concentrations decrease d within 3 days for both carotenoids. The average decreasing slopes fo r the two carotenoid pigments were parallel, indicating a similarity i n the rate of which astaxanthin and canthaxanthin are utilized by rain bow trout. The serum dose-response of trout that received dietary keto -carotenoids increased with increasing pigment levels. The hypothesis that absorption of dietary carotenoids in 12.5-200 mg/kg range of conc entration across the gut wall may be by passive diffusion is proposed.