Chromosome studies on the mitten crabs Eriocheir japonica and E. sinensis

ABSTRACT: In recent years, there has been debate from various perspectives on the question of whether the mitten crabs Eriocheir japonica and E. sinensis should be considered as two different species. It has been reported that the chromosome numbers of these two crabs differ from each other; for E. japonica it is 2n = 148, n = 74, whereas for E. sinensis it is 2n = 146, n = 73. These data suggest that E. japonica and E. sinensis are different species. Nevertheless, the chromosome number of E. japonica was obtained in 1937 by the method of paraffin section. This classical gonad (testis) sectioning method is now known as an unreliable method for determining the number of chromosomes. In the present study the number of chromosomes in E. japonica and E. sinensis is re-examined using the air-drying method. The results show that E. japonica and E. sinensis have the same number of chromosomes (2n = 146, n = 73), which means that the number of chromosomes cannot be used as a criterion to distinguish these two species. Even though observation of the chromosomes under the scanning electron microscope was attempted, it was not possible to perform karyotype analysis in the two species because centromeres could not be identified in some of the chromosomes.