There are many evidences that carotenoids may act as antioxidants and protect humans from serious disorders such as skin degeneration and aging, cardiovascular disease, certain types of cancer, and age-related diseases of the eye. Carrots (Daucus carota L.) are consumed as an important dietary source of b-carotene, a-carotene and lutein. Astaxanthin, a keto-carotenoid has been used to raise red color of fish body and to improve immune activity in fish-breeding industry. In this study, transgenic carrot plants were generated to overproduce carotenoids including astaxanthin, a non-natural ketocarotenoid in this plant, using an efficient storage root-expression system. Among the nineteen transgenic carrot plants, transformed by a storage root-specific (ibMads) or a storage root (ibAGP1) or the constitutive CaMV35S promoters with three genes involved in carotenoid synthesis [Psy (Phytoen synthase), Crtl (Lycopen-β-cyclase), CrtO (β-carotene ketolase)], transgenic plants with ibAGP1 promoter, an amyloplast targeting sequence (TP1) and a single CrtO gene gave high content of keto-carotenoids and b-carotene. For fish body coloration, carotenoid extract or astaxanthin significantly made the body color of red seabreams more reddish than those of normal diet-fish in the 3 weeks feeding. In addition, the serum lysozyme activity in carotene-treated fish was significantly higher than that in normal diet-fed fish (P<0.05) in the 6 weeks feeding. In these cases, neither carotenoid extract- nor astaxanthin-contained diet did influence on growth rate and food utilization in red seabreams. These results suggested that carotenoid extract prepared in the present study may be useful in the body coloration and the enhancement of nonspecific immune response of red seabreams. Meanwhile, b-carotene (50 mM) up-regulated peroxisome proliferator-activated receptor a expression (PPAR-a) by about two fold in CV-1 cells, while the carotenoid extracts and astaxanthin failed to affect on the expression. Carotenoid extracts (250 mg/ml) from wild type carrot or transgenic carrots showed moderate DPPH scavenging activity.