The Fishotron is a quest item that is needed for the Angler. It can be obtained by fishing in any pure underground waters.
I don't know what's worse, a bone fish or a bone fish with HANDS. This Fish-o-Tron deep in the caverns really freaks me out! I think it's possessed by the same evil spirits that possessed that old man by the dungeon! I double duck dare you to go catch it!