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Not quite a creature that invokes fear, but definitely grouped in with the fictional group of North American creatures, known as fearsome critters, the fur bearing trout is a fish that supposedly grows a thick coat of fur.
The origin story of this alleged critter stems from the extremely cold waters of the lakes and rivers in the northern U.S, it is said that the fish reach the cold waters and grow fur. The first account of the folklore appeared in 1929, but it is said that people in Arkansas had known of the fur covered fish for centuries.
Iceland has a similar folktale, although slightly darker. The Lodsilungur is the Icelandic furred fish, supposedly the creation of demons and giants. An inedible fish that fills the waters as a punishment for the evils of mankind. The Icelandic furred fish is covered in vivid red hair.
While there are no real furred fish, there is a white, cotton-like mold,
Saprolegnia, that can give certain fish the appearance of having tufts of white hair.