Wild Red Belly Piranha (Pygocentrus nattereri)

Piranha replace their teeth in a genuinely unusual pattern: rather than losing individual teeth at random like most animals, an entire quadrant of the jaw drops and regrows together, alternating sides so there's always a fully functional set of interlocking teeth ready to bite. Wild-caught fish like this one bring home the real deal — that classic fiery red belly and a temperament that actually mellows out in a proper shoal rather than kept alone.

Care level: Moderate · Temperament: Semi-aggressive, shoaling · Max size: ~10" · Min tank: 75 gal · Diet: Carnivore, meaty foods