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 very deadly when in the water, and unless dealt with carefully, they can pose a viable threat in swarms. They swim much faster than most fish, so it is recommended that you stay out of the water until there are relatively few remaining.

Trivia

 * Arapaima are the largest freshwater fish native to South America, sometimes reaching lengths of more than 2 meters.