What order includes piranhas and tetras?

What order includes piranhas and tetras? The answer is Characiformes.

Characiformes is the order of ray-finned fishes that includes piranhas, tetras, characins, and numerous related freshwater groups. Most species live in South and Central American rivers and lakes, although several characiform families are native to Africa.

The order contains many small, schooling fishes prized in aquariums, including neon tetras and other brightly colored species. It also includes larger or more specialized forms: piranhas are members of the family Serrasalmidae, while African groups include distichodontids, citharinids, alestids, and hepsetids.

Characiformes belongs to the otophysan branch of bony fishes, alongside orders such as Cypriniformes and Siluriformes. Many characiforms possess a Weberian apparatus, a chain of bones linking the swim bladder to the inner ear and helping with sound detection and balance. Most have scales and many have teeth, reflecting diets that range from insects and plants to other fish.

Piranhas and tetras are therefore not separate orders. They are very different-looking members of one broad evolutionary order, although classification within Characiformes continues to be refined as genetic studies revise relationships.