Gymnocorymbus

The silver tetra, Gymnocorymbus bondi, is a characid from the Rio Orinoco basin in Colombia and Venezuela. It inhabits small tributaries, streams and creeks. Juveniles have reddish unpaired fins that fade as they mature, and the fairly bland adults are not often seen in the hobby. Peaceful and hardy, it is sometimes labelled G. socolofi, a name now considered a junior synonym of G. bondi.

The black widow tetra, Gymnocorymbus ternetzi, is a characid from the Rio Paraguay and Guaporé basins in Brazil, Bolivia and Argentina. All the fish in the trade are captive bred and unfussy about water chemistry and diet. The intense black of juveniles fades as they grow. Long-finned and 'golden' (leucistic) forms exist, the latter often sold as the 'white skirt tetra', and artificially dyed fish also turn up, a stressful process that often shortens their lifespan considerably.