Spinous loach, Cobitis biwae, lives in slow-flowing and stagnant waters in Honshu, Shikoku and the eastern part of Kyushu. There are two local races in spinous loach different in body size. The small race of the Kantô district is diploid with 48 chromosomes and the large race of the Kansai district is tetraploid with 96 chromosomes. Both races were examined for the relationship between the somatic chromosome number and erythrocytic size. The small race from Aki River, Tokyo, had 48 chromosomes with small erythrocytes and the large race from Yoshii River, Okayama Pref., had 96 chromosomes with large erythrocytes. The ratios of surface areas of the tetraploid erythrocytes and of their nuclei to those of the diploid ones were 1.62 and 1.74, respectively. These results show that tetraploid spinous loach is exactly discriminated from diploid one by the determination of erythrocytic size.
The Japanese Society of Fisheries Science