The tryosinase activity and the concentration of carotenoids and luteins in blood serum,skin and squama of seven freshwater fishes,such as Ctenopharyngodon idellus,Carassius auratus auratus,Megalobrama amblycephala,Pelteobagrus fulvidraco,Monopterus albus,Misgurnus anguillicaudatus and Ictalurus punctatus,were determined in order to discover the differences among species and the different parts of the same fish.The results showed that the tryosinase exists in blood serum,skin and squama.The concentration of carotenoids and luteins in skin and squama also have remarkable difference among different species.Concentration of carotenoids and luteins in backside and belly skin of Monopterus albus and Misgurnus anguillicaudatus were higher than other species(P<0.05).Concentration of carotenoids and luteins in skin and serum of ctenopharyngodon idellus,carassius auratus auratus and megalobrama amblycephala were also high.Concentration of carotenoids and luteins in backside skin were higher than that in belly skin for the same kind of fish.From this experiment,we know that melanin and carotenoids both have effect on the skin colour of fish.The depth of yellowness has a direct connection with the concentration of carotenoids and luteins;Besides,the depth of blackness also has a direct connection with the tryosinase activity.