From the Super Mario Wiki
Battle Salmon are mechanical fish in the Smithsnorian Museum of Wario: Master of Disguise. They appear in an underwater part of the museum. They are thin fish that to do damage by colliding into Wario and destroying themselves. 23 appear in the game.
A paper-thin fish that moves with the speed of 10,000 winds and sacrifices its own life to damage enemies. ...What a jerk.
Names in other languages