Carassius praecipuus, a dwarf new species of goldfish from the Mekong drainage in central Laos (Teleostei: Cyprinidae)

Carassius praecipuus, new species, is described from a hill stream in the upper Nam Ngum watershed in Mekong drainage in central Laos. It is distinguished from all congeners by the short dorsal fin, a small number of branched dorsal-fin rays, lateral line scales and gill rakers. It reaches sexual maturity around 70 mm SL. This is the first species of the genus discovered outside East and North Asia and Europe. The upper Nam Ngum watershed includes a part of the Plain of Jars, which had been hypothesised to have allowed the movement of a number of fish lineages between the rivers flowing to the Gulf of Tonkin and the Mekong drainage.