Flesh pigmentation of rainbow trout fed astaxanthin or canthaxanthin at different feeding rates in freshwater and saltwater

Abstract

Rainbow trout with a mean initial weight of 111 g were fed diets supplemented with 25 or 50 mg astaxanthin or canthaxanthin/kg for 8 weeks. The five diets, including a control diet without carotenoid supplement were fed at feeding rates (FR) of 0.5, 1.0 and 1.5% body weight (BW)/day in freshwater and 1.0% in saltwater. Significant differences in growth and feed conversion were caused only by feeding rate. FR=0.5% resulted in a significantly slower growth than the other two. The feed conversion was not significantly different between FR=0.5% and FR=1.0%, while the values obtained for the trout fed FR=1.5% were higher. The trout fed diets with astaxanthin contained about 1.5 times more carotenoids in the flesh than those fed diets with canthaxanthin. A diet containing either 25 mg astaxanthin or canthaxanthin/kg resulted in an average carotenoid concentration of 2.1 mg/kg flesh. There was a tendency toward lower carotenoid content in the flesh of the fish fed at FR=0.5% than at the other two feeding rates. The retention of carotenoids in the flesh was significantly different for the two carotenoid sources (retention of astaxanthin, 11.4%; canthaxanthin, 7.1%) and feeding rates (12.5% retention at FR=0.5%, 9.3% retention at FR=1.0% and 6.1% retention FR=1.5%). There was a tendency toward higher retention for the lower dietary carotenoid concentration. A comparison between the trout in saltwater and freshwater did not reveal significant differences in growth, feed conversion and carotenoid retention. The carotenoid concentration in the flesh, however, was higher in freshwater (2.2 mg/kg) than in saltwater (1.7 mg/kg).