More than 150[1] Tetra is the common name of many small freshwater characiform fishes.

Many of these, such as the neon tetra (Paracheirodon innesi), are brightly colored and easy to keep in captivity.

It is short for Tetragonopterus, a genus name formerly applied to many of these fish, which is Greek for "square-finned" (literally, four-sided-wing).

Tetras generally have compressed (sometimes deep), fusiform bodies and are typically identifiable by their fins.

Ichthyologists debate the function of the adipose fin, doubting its role in swimming due to its small size and lack of stiffening rays or spines.