Phylogeny and species diversity of the South and southeast Asian cyprinid genus Danio Hamilton (Teleostei, Cyprinidae)

Danio Hamilton, in the wide sense, consists of 66 nominal species, of which about 45 are valid. Four species, viz. D. kakhienensis, D. laoensis, D. shanensis and D. browni, were revalidated in papers revising the genus. Six species were found to be new to science: Danio maetaengensis from northern Thailand; D. kyathit from northern Myanmar; D. apopyris, D. acrostomus and D. leptos form northern Laos; and D. roseus from northeastern Thailand and northwestern Laos. Daniops myersi was confirmed to be a junior synonym of D. laoensis. Three species groups have been recognized among Danio (s. l.) species based mainly on colour pattern and other morphological characters: the striped danios, the barred danios and the Danio dangila species group. The striped danios differ from barred danios in having more branched dorsal-fin rays, a complete lateral line, two pairs of short barbels and a P stripe extending to the end of the caudal-fin rays (instead of the P stripe being confined to the caudal peduncle). A few characters common to both striped and barred danios but absent in the Danio dangila species group are, e. g., a cleithral spot immediately behind the gill-opening and a skin groove on the supraorbital shelf. A phylogenetic analysis shows that Danio is paraphyletic. Two monophyletic groups can be recognized within the non-monophyletic genus Danio, one comprising only the Danio dangila species group, and the other including all the striped and barred danios. The first group thus represents the genus Danio (s. str.), and the latter a distinct genus Devario, with the type species D. devario. The monophyly of Danio is strongly supported, and its sister group is Esomus. Chela and Inlecypris are closely related to each other, and they form the sister group of Devario. Brachydanio is confirmed to be a junior synonym of Danio (s. str.). Danio erythromicron is excluded from both Danio (s. str.) and Devario. Its generic status is pending further study. The phylogenetic relationships of Sundadanio axelrodi and Danionella translucida to Danio (s. str.) and Devario remain unresolved.