Golden Carp

Golden Carp are a type of fish which are found extremely rarely by fishing in any biome in any layer, with the exception of the Desert /  an Ice biome that is Corrupted, Crimsoned, or Hallowed. Their sole use is to be sold for a large amount of coins.

Trivia
It has been observed that Golden Fishing Rods tend to reel in more Golden Carp than other rods, however this isn't proven and could simply be coincidence.