Mimagoniates is a genus of characid fish from rivers and streams in southern and eastern Brazil, northeastern Argentina and Paraguay. Commonly known as croaking tetra or chirping tetra because they can produce sounds, some of these fish were formerly included in Glandulocauda. They have a supplementary breathing organ located above the gills which makes a faint chirping sound when these fish come to the surface to gulp air. It also plays a role in courtship as the male chases and hovers near the female while taking gulps of air and expelling it to make a rhythmic noise. Croaking behavior may have evolved from a behavior called "surface nipping", which occurs when the fish is searching for food. This gulping of air has no useful respiratory function.