The Piranha is a hostile Mob in Mechanic Miner.
The Piranha can only be found in the marsh in the first lake you'll meet.
Nearing the Piranha will aggravate it, and cause it to attack you. The Piranha is fairly fast, but can only move in water, thus it will only attack the player when he's in the water.
The Piranha will drop experience on death, and can be harvested for Fish Oil.