Arapaima

The Arapaima is a Hardmode fish-type enemy that appears in the Jungle/Underground Jungle. It is immune to the Confused debuff. They are an easy enemy to kill if one starts hardmode with a weapon such as the Night's Edge, or makes a Hardmode sword like a Cobalt Sword or Palladium Sword.

Trivia

 * Arapaima are the largest freshwater fish native to South America, sometimes reaching lengths of more than 2 meters.
 * They were once featured in an episode of "River Monsters" (a fishing special on Animal Planet).