Rasboras and Danios: close cousins in tropical Asia

Rasboras and Danios are cyprinids that are so closely related that you'd be hard pressed to describe the difference between them: danios generally sport barbels but rasboras never do. Maurice Kottelat and his co-workers are beginning to see the genus Rasbora as a kind of catch-all casserole, out of which they have been pulling separate genera, like the anagrammatic Boraras micros — its minute relative B. maculata appears in some of Takashi Amano's aquaria and turns up on the market sometimes — and a couple of Microrasbora species, the kind of fishes Dr Paul Loiselle called "eyestrain rasboras" in Amazonas July/August 2012. Even the colorful Rasbora axelrodi now has its own genus, Sundadanio: "danio of the Sunda Isles."
 
In 2003 Fang Fang restricted Danio to our familiar Danio rerio and some close allies and set the others apart as Devario. In 2010 Liao has done the same for the Rasborins (Rasbora and allies) employing DNA analysis to supplement morphology.
 
A bucketful of new Danionin species have been found in the last five or six years. Even more from the waters of Burma await formal description. Wikipedia has a list of Danionin species to help guide you through the new thicket. 
 
These small schooling fishes fill the same ecological niches in India and South-East Asia that Characins fill in South America. Investigators found that insects were the primary food of Danio and Devario species in their home waters, supplemented by minute crustaceans and algae and detritus. 
 
Link. Czech aquarists Jaroslav Elias and Frantisek Podvesky's general article, "The minnows called Barbs,  Danios and Rasboras",  is archived at Wet Web Media. 
 
Rasbora at Wikipedia. Rasbora (including former Rasbora) at FishBase.
 
Danio at Wikipedia. Danio (including former Danio) at FishBase.