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Rainbow trout (Oncorhynchus mykiss) with a mean (SD) weight of 120 (2)g were fed diets supplemented with astaxanthin extracted from the yeast Phaffia rhodozyma (OYl = 50 mg carotenoids kg& feed, OY2 = 100 mg carotenoids kg-' feed), astaxanthin (AX = 100 mg astaxanthin kg-' feed) and canthaxanthin (CX = 100 mg canthaxanthin kg' feed) for 4 weeks. Muscle analyses at the end of the experiment indicated a significantly higher carotenoid concentration in the AX group, while CX and OYl groups were similar in spite of the differences in dietary concentration. The measure of total muscle colour difference (AE*& between initial samples and 4 week ones was higher for the AX fish group but showed no significant difference between OYl, OY2, and CX. The hue and the reflectance ratio (f&,o:R~lo) of fish muscle increased in proportion to carotenoid intake. Digestibility (ADC) of yeast astaxanthin in OYl and OY2 groups was significantly higher than that in the AX group. Canthaxanthin ADC was about one sixth of that of astaxanthin (AX group). Carotenoid retention in the muscle, expressed as a percentage of carotenoid intake, was higher for the AX group than that recorded for OYl and OY2. According to ADC, carotenoid retention showed a marked lower value for the CX group. Muscle retentions were similar for astaxanthins from both sources.

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