Gastromyzon

H. H. Tan & Z. H. Sulaiman, 2006, Three new species of Gastromyzon (Teleostei: Balitoridae) from the Temburong River basin, Brunei Darussalam, Borneo., Zootaxa 1117, pp. 1-19 : 1

[[ Gastromyzon ]]

The genus Gastromyzon , a unique group of fishes endemic to the island of Borneo, exhibits extreme morphological adaptations for life in torrential waters. The included species, which are obligate bottom dwellers, are poor swimmers that have lost the ability to hover or swim in mid-water. As a consequence, the genus has evolved new modes of locomotion, which involve creeping and crawling along the bottom. Balitorid locomotion had been studied by Wickler (1971) using aquarium stocks of G. ctenocephalus (misidentified as G. borneensis ). He found that the horizontally oriented pectoral fins, fused pelvic fins, and depressed head and body collectively form a suction cup that enables the fish to adhere to the submerged rock substrate of fast flowing streams. The genera Gastromyzon , Hypergastromyzon and Neogastromyzon are characterized by fused pelvic fins; and a higher number of branched pectoral and pelvic-fin rays (numbering 20-30 and 16-24 respectively) than are found in the other 250 or more species of cyprinoids in the Sunda Islands, in which the number of branched pectoral rays does not usually exceed 17 and branched pelvic rays does not exceed 12 (and is usually not more than 8; Inger & Chin, 1961). Unicellular horny projections, or unculi, on the ventral surfaces of the fish’s body apparently also serve to increase adhesion on smooth rocky surfaces (Roberts, 1982a, 1982b, 1989).