A Revision of the Asian Mastacembelid Fish Genus Macrognathus

Abstract

The highly specialized Asian mastacembelid genus Macrognathus, hitherto considered monotypic, comprises three morphologically distinct species with nearly contiguous ranges: M. aral, from the Indian subcontinent, including Sri Lanka and Burma; M. siamensis, from the Chao Phrya and Mekong basins of Thailand and Kampuchea, and the northernmost part of the Malay peninsula; and M. aculeatus, from the southern Malay peninsula, Sumatra, Borneo and Java. The species differ sharply in number of rostral toothplates and other meristic characters as well as in coloration. The specific status of M. aculeatus from Java, and that of M. dhanashorii from Assam (placed here as a synonym of M. aral), should be reconsidered when adequate study material becomes available. Mastacembelidae form two groups, possibly phyletic, based on structure of the rim of the anterior nostril. All or almost all African Mastacembelus and several Asian species (usually the larger species, including M. mastacembelus) have the nostril rim with two flaps and two fimbriae, whereas Macrognathus and several smaller species of Asian Mastacembelus (including M. pancalus and M. circumcinctus) have the nostril rim with six fimbriae.