Differentiation of Freeze-Thawed Fish from Fresh Fish by the Examination of Blood

Abstract

At present, a large number of freeze-thawed fish have been sold without being distinguished from fresh fish at the final stage of marketing. It is important to establish a practicable method for differentiating freeze-thawed fish from the fresh one. Some studies have been reported on the differentiation, which is by means of the observation of the destruction of the red blood cells by a microscope, the opacity of the central part of the crystalline lens and the enzymatic methods.
In the present study, the author employed the hematocrit value as the destruction index of red blood cells in the unfrozen and the freeze-thawed fish. The experimental results obtained by carp indicated that the changes in hematocrit values during the unfrozen and the frozen storage reflected well the destruction degrees of red blood cells. In the case of many species of commercial freeze-thawed fish, all their hematocrit values closed upon 0%. Since the microscopic observation of the destruction of the red blood cells is trouble some, the author insists that the determination of hematocrit value is the simplest to differentiate the freeze-thawed fish from fresh one.