Karyotypes and distribution of nucleolus organizer regions in four cyprinid species from Thailand

Abstract

Rainboth (1996b) has varified all Puntius species of Smith (1945) into 4 genera, Puntius, Systomus, Barbodes and Hypsibarbus by taking their distinctive external morphological differences into account. Since cytotaxonomy by the studying of karyotypes and distributions of nucleolus organizer regions (NORs) might provide possible useful data to support such taxonomic problem or vice versa. This study was therefore designed to do comparative study by examining some external morphological features but emphasizing on the comparison of karyotypes and distributions of NORs of a representative cyprinid species of those above 4 genera, they are Puntius brevis, Systomus orphoides, Barbodes gonionotus and Hypsibarbus wetmorei, respectively. The fish materials in this study were obtained from middle plain of the Chao Phraya river system. Each species was taken at the place as many as enough for selection. For morphometric and meristic studies ten specimens of each species were encountered. Whereas another ten specimens of both Barbodes gonionotus and hypsibarbus wetmorei, eight specimens of Puntius brevis and 6 specimens of Systomus orphoides were used for the studies of karyotypes and distribution of NORs. From the obtainable data on the external morphology of the sole representative species of the four genera, they exhibit a number of distinctive feature to render the agreeable separation of the species at the generic level. To support the above taxonomic throught, this further study on karyotypes and distributions of NORs have shown that although all the four species of different genera has similarly 50 diploid chromosome number(2n), however, the combinations of chromosome types, arm number (NF), number and location of NORs are likely different. For Puntius brevis, the karyotypes comprise of 2m, 2sm, 2st and 44a; 54 for NF and NORs have one pair which locate on the satellited regions of a subtelocentric pair on short arms. Systomus orphoides, the karyotypes comprise of 12m, 20sm, 4st and 14a; 82 for NF and NORs have one pair which locate on the satellited regions of a submetacentric pair on short arms. Barbodes gonionotus, the karyotypes comprise of 6m, 16sm, 6st and 22a; 72 for NF and NORs have two pairs which locate on the satellited regions of a submetacentric pair on short arms and on the satellited regions of an acrocentric pair on short arms. Hypsibarbus wetmorei, the karyotypes comprise of 12m, 4st and 55a; 74 for NF and NORs have one pair which locate on the satellited regions of an acrocentric pair on long arms.