Arapaima

The Arapaima is a fish-type enemy that is immune to the Confused debuff. This enemy appears after the Wall of Flesh has been defeated and the world has entered Hardmode, and appears in the Jungle, Crimson and Underground biomes. 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. They were once featured in an episode of "River Monsters" (a fishing special on Animal Planet).