fisher, name of a large North American marten, Martes pennanti. This carnivorous, largely arboreal mammal is found in hardwood forests of Canada, the extreme N United States, and mountain ranges of the W United States. Fishers have dark brown fur shading to black and frosted with white-tipped hairs. Males are over 3 ft (90 cm) long, including the bushy tail, which may reach 15 in. (38 cm), and weigh 6 to 12 lb (1.8–3.6 kg); females weigh about half as much. Active both by night and by day, on the ground and in trees, the fisher makes its den in a hollow tree or a hole in the ground. It feeds on small mammals, birds, carrion, and fruits. Despite its name, it does not catch fish, although it will eat them. It is one of the few animals that eats porcupines, which it attacks by striking at the unprotected underparts. The fisher is not abundant and is difficult to trap; its beautiful fur brings high prices. Once considered threatened with extinction, fishers are now increasing in numbers. They are classified in the phylum Chordata, subphylum Vertebrata, class Mammalia, order Carnivora, family Mustelidae.