This study was designed to test the effects of dietary astaxanthin on growth, muscle pigmentation, antioxidant activity and biochemical composition of juvenile rainbow trout (Oncorhynchus mykiss). Experimental diets were formulated to contain 50, 75 and 100 ppm astaxanthin (designed as AS50, AS75 and AS100). The diet without supplementation of astaxanthin was considered as the control diet. Each experimental diet was fed to three replicate groups of fish (18.5 g/fish) to visual satiation two times a day for 10 weeks. Growth performance and proximate composition of muscle of fish were not affected by dietary AS levels (P> 0.05). Total carotenoid concentration in the muscle of fish fed the AS50 diet was higher than that of fish fed the control diet, but no different to that of fish fed the AS75 and AS100 diets. The astaxanthin concentration in the muscle of fish fed AS50, AS75 and AS100 diets were higher than that of control diet. The redness (a*) of the muscle of fish fed AS50, AS75 and AS100 diets were higher than that of fish fed the control diet (P 0.05) nije uticao na performansu rasta i hemijski sastav mišića ribe. Ukupna koncentracija karotenoida u mišiću ribe koja je hranjena AS50 hranom bila je viša nego kod riba hranjenih kontrolnom hranom, ali nije bila drugačija od riba hranjenih AS75 i AS100 hranom. Koncentracija astaksantina u mišiću riba hranjenih AS50, AS75 i AS100 hranom bila je viša nego kod riba hranjenih kontrolnom hranom. Crvena boja (a*) mišića ribe koja je hranjena AS50, AS75 i AS100 hranom bila je jača nego kod ribe hranjene kontrolnom hranom (P< 0.05). Antioksidantna aktivnost DPPH, radikala hidroksila i alkila u plazmi i jetri riba nisu zavisili od nivoa astaksantina osim kod plazme koja je imala antioksidantnu aktivnost alkilnih radikala. Rezultati ove studije nagoveštavaju da se hrana koja sadrži 50 ppm astaksantina može koristiti da bi se poboljšala crvena boja mišične pigmentacije kod mlađi kalifornijske pastrmke
