Gastromyzon

[[Gastromyzon]] The genus Gastromyzon, which is endemic to Borneo, exhibits extreme external morphological adaptations for life in torrential waters. Obligate bottom dwellers, the included species have lost the ability to hover or swim in the mid-water column, and as a consequence have evolved new modes of locomotion, which involve creeping and crawling over submerged rocks. Locomotion in the genus has been studied by Wickler (1971) using aquarium stocks of G. ctenocephalus (misidentified as G. borneensis). The horizontally oriented pectoral fins, fused pelvic fins, and depressed head and body collectively form a suction cup, which enables the fish to adhere to the submerged rocky substrate of fast-flowing stream habitats. In addition, the genus is characterized by greater numbers of pectoral and pelvic-fin rays, these numbering 20-30 and 16-24 branched rays, respectively. This compares to the other 250 or more species of cyprinoids in the Sunda Islands, in which the number of branched pectoral rays usually does not exceed 17 and the number of branched pelvic rays does not exceed 12 (with the latter usually no more than 8; Inger & Chin, 1961). Unicellular horny projections, or unculi, on the ventral surfaces of the fish apparently also serve to increase adhesion on smooth rock surfaces (Roberts, 1982a, 1982b, 1989). The morphological adaptations described above are shared by the closely related balitorid genera Hypergastromyzon and Neogastromyzon, which are also endemic to Borneo. During the course of a taxonomic revision of Gastromyzon, collaborations were made with regional scientists to facilitate research and collections, which resulted in discovery of the three new species described in this paper.
Published as part of H. H. Tan & C. U. M. Leh, 2006, Three new species of Gastromyzon (Teleostei: Balitoridae) from southern Sarawak., pp. 1-19 in Zootaxa 1126 on pages 1-2