PIGMENTATION OF RAINBOW-TROUT FROM START FEEDING TO SEXUAL-MATURATION

Rainbow trout were fed diets supplemented with either 100 mg astaxanthin/kg [(3S,3'S)-, (3R,3'S)-, (3R,3'R)-optical isomers; 1:2:1 ], 100 mg canthaxanthin/kg, or without carotenoids added in an experiment lasting for 140 weeks. During the experiment the fish weight increased from 0.13 g to 3 kg. From weeks 23 to 58 after start feeding, astaxanthin was significantly more efficiently utilized for flesh pigmentation than canthaxanthin. The carotenoid concentration in flesh of immature trout fed diets with carotenoids reached a final level of 20 mg/kg. The carotenoid concentration in skin of immature trout fed carotenoids increased during the first 49 weeks and decreased thereafter. The carotenoid concentration in skin of trout fed astaxanthin tended to be higher than that of the fish fed canthaxanthin, while the opposite was found for liver. The total carotenoid contents of sexually mature females and males were 73-79% and 18-19% of that in the immature fish, respectively. The carotenoid content in female gonads increased moderately with sexual maturation, and the carotenoid content in skin of males increased strongly. No significant difference was observed between optical isomer composition of astaxanthin in the flesh and that in feed. Skin of fish fed astaxanthin mainly contained astaxanthin esters and skin of fish fed canthaxanthin contained canthaxanthin and its reductive metabolites. A slight accumulation of the (3S,3'S)-isomer of astaxanthin was observed in skin. This was rationalized by accompanied accumulation of (3S,3'S)- and (3R,3'S)-zeaxanthin.