A 126-day experiment was carried out under controlled conditions to compare the effects of five levels (50, 100, 150, 200 and 250 mg kg-1) of annatto seed meal (ANS) on the blood carotenoid content (BCC) and fillet color stability of rainbow trout (87.25±1.42 g). BCC increased significantly (p<0.05) in fish fed the diets containing 200-250 mg kg-1 ANS compared to other diets. There was a significantly (p<0.05) linear regression (r2=0.75) between BCC and fillet carotenoid content. At the end of experiment, there were significantly (p<0.05) positive relationships between BCC and final weight and specific growth rate (SGR), while a negative relationship was observed between BCC and feed conversion ratio (FCR). Fillet color parameters (L*, a* and b*) were significantly (p<0.05) correlated to BCC in the rainbow trout fed dietary ANS. There were no significant differences in the carotenoid content of refrigerated (4°C) stored fillet after 14 days. The significantly (p<0.05) least loss of total carotenoid content in the frozen stored fillets after 6 (8.4%) and 12 months (19.2%) were observed for fish fed the diets containing 250 mg kg-1 ANS. The frozen stored fillets of fish fed the diets containing from 100 to 200 mg kg-1 ANS showed significantly (p<0.05) lower total carotenoid content loss (27.2-36.0%) than those of fed the astaxanthin-based diet (70.5%) and control (88.78%) after 12 months. The present results showed that dietary ANS exerted positive effects on BCC and color stability of fillets.

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