Seems to be some fantasy thing :
"The Mushtash Fish eats wood, and especially likes backyard decks. Beware bringing them home, for they will jump out of the tank to find any source of wood, and then grow at an alarming rate. They are known to grow from a polite minnow-sized aquarium fish to a hefty three-foot monster within minutes. They are capable of staying out of water for an hour, and stomping on them will not kill them (be careful of the secondary mouth on its back!). Several dashes of pepper is your best choice against this common pest."

http://elfwood.lysator.liu.se/art/t/a/taski/mushtashfish.jpg.html