S.A. Redtail Catfish (Phractocephalus hemioliopterus)

Redtail catfish are one of the most infamous "outgrows the tank" fish in the hobby: a cute six-inch juvenile with a vivid red tail that, given years and a steady diet, becomes a four-foot-plus adult capable of swallowing tankmates whole. Anyone taking one home should already have a plan for the 500-gallon-plus setup it'll eventually demand — this isn't a fish you grow into gradually.

Care level: Moderate · Temperament: Peaceful, predatory to small fish · Max size: ~48"+ · Min tank: 500+ gal (adult) · Diet: Carnivore, live/frozen meaty foods