Abstract
Catlocarpio siamensis Boulenger is a gigantic cyprinid of the subfamily Barbinae occurring in the Menam Chao Phrya River in Thailand and the Mekong River systems in Laos, Cambodia and Vietnam. Due to its morphological resemblance to the Indian and Burmese Catla catla (Hamilton-Buchanan), this species has often been assigned to the genus Catla or even identified as Catla catla (or its synonym, Catla buchanani).
Karyologically, Catla catla is known to be a diploid species with a diploid chromosome number of 50 (Manna and Khuda-Bukhsh, 1977), but the chromosomes of Catlocarpio siamensis have not been studied. In the present study, we found that Catlocarpio siamensis has a diploid chromosome number of 98 and most probably there is a diploid-tetraploid relationship between the two species.
