In the 19th century, Americans and Canadians began importing and releasing several fish into the wild, most from northern Europe. [source] Within Icelandic waters, the rare fur-bearing trout generally laid their eggs among those of the brown trout. Found above instead of under the gravel, those who sought brown trout eggs accidentally gathered the other's young; identical in appearance, the unknown, unstudied species was carried away without notice. 

Raised as game fish or part of aquaculture, animals that had never encountered each other in the wild were suddenly sharing space. Fish enthusiasts also kept multiple species in the same tank or pond, hoping to cross-breed them. Some of these attempts were successful; likewise, new species resulted from the animals' newfound proximity throughout the continent. Because of this, there are many hybrid trout in North America: tiger, splake, cutbow, and palomino. [source] 

Fur-bearing trout are also hybrids; like the cutbow, their hybridization occurred naturally, and they are flourishing hybrids. A rarity, these animals can successfully breed, the next generation able to bear young…