How mesmerizing are Penguin Tetras!? It’s very easy to tell why these guys are so popular! Penguin tetras stay small (about 2 inches) and are a gorgeous addition to community aquariums. These tetras are known to nip long fins. However, if kept in a large enough school, that behavior is rarely seen. They are peaceful and do good with other tetras such as bloodfins, serpaes and emperor tetras. They also do good with most rasboras and small catfish. Penguin tetras are omnivorous so should be fed a high quality pellet with frozen foods such as bloodworms on the side.