Differentiation of freeze-thawed fish fillet from fresh fish fillet by the examination of erythrocyte

A method for differentiation between fresh and freeze-thawed fillets was tested by the use of a trace amount of blood and dark muscle collected from the fillets. The differentiation was accom-plished according to whether intact erythrocytes were recognized or not in the blood and dark muscle. A large number of fresh, refrigerated, and freeze-thawed fillet samples were prepared from red sea bream and Pacific mackerel. A 20 μl or less volume of blood was withdrawn with a capillary tube from the ventral or dorsal aorta of the samples, smeared on a slide glass, dried, and examined microscopically for the presence of intact erythrocytes after staining with Giemsa solu-tion. Besides, a samll amount of surface dark muscle was taken from the samples, smeared on a slide glass, and examined similarly. As the results, intact erythrocytes were recognized in the blood and dark muscles collected from fresh and refrigerated samples but not in those from any freeze-thawed samples. All erythrocytes were destroyed in the freeze-thawed samples. Commercial fillets of flat fish, hair tail, and red horse head and flesh block of tuna were obtained from the market. In the case of these samples, it was also successful to differentiate fresh fillet and fresh block from freeze-thawed by this method.