Piranha

The Piranha can be found in water pools of the Jungle, Underground, and Cavern layers. They have an increased spawn rate in the Jungle. They swim in a straight line left or right until hitting a wall, where they flip directions. They will swim towards the player if he/she is submerged in water; otherwise they pay no attention to the player. It moves its tail back and forth and swims in a slight zig-zag. Piranhas become Angler Fishes when your world enters Hardmode, however; the piranha spawn is still active in jungle biomes.

History
Piranha Piranha Piranha Пиранья