DIGESTIBILITY OF ASTAXANTHIN AND CANTHAXANTHIN IN RAINBOW-TROUT AS AFFECTED BY DIETARY CONCENTRATION, FEEDING RATE AND WATER SALINITY

The digestibility of astaxanthin and canthaxanthin in rainbow trout wa s studied in two different experiments. In the first experiment, the t rout were fed, at a rate of 1.0% body weight/day (BW/d), diets contain ing various concentrations (12.5, 25, 50, 100 and 200 mg carotenoid/kg feed) of astaxanthin or canthaxanthin in fresh water. The overall app arent digestibility of astaxanthin was higher than that of canthaxanth in whatever the dietary concentration of the carotenoid. Apparent dige stibility coefficients were maximum for astaxanthin (79.1 +/- 1.3%) at 25 mg/kg feed and for canthaxanthin (68.6 +/- 2.8%) at 50 mg/kg feed, and then decreased at higher dietary levels of carotenoids. In the se cond experiment, only diets containing 25 or 50 mg carotenoid/kg feed of either of the two carotenoids were fed to trout in fresh water at f eeding rates of 0.5, 1.0 and 1.5% BW/d, and in sea water (30-32 ppt) a t a rate of 1.0% BW/d. Neither the feeding rate nor the salinity affec ted the digestibility of the two carotenoids.