I believe it was PFK’s Matt Clarke who first coined the phrase Danionins back in 2009.
Danios are currently split into two main genera, Danio and Devario, but the group also includes some close relatives like Sundadanio, Danionella and Microrasbora. Rather than call these fish Danios, Matt was suggesting that we call all of the fish in the group “Danionins”, rather than danios.
Quite often you will hear that all “Danionins” are fastswimming, midwater or surfacedwelling fish, that generally live in large groups of 20 or more in fastflowing shallow rivers and streams. At one time that characterization might have been true, but not with today’s “Danionins”.