The fisher, also known as the ‘fisher cat’, is a large, dark, long-haired member of the weasel family. Their stature is relatively low to the ground, with short legs, small ears and a well-furred tail. The color of their fur varies from dark brown to nearly black. Females and juveniles usually have a more uniform color, and males will have a blonde or grizzled appearance due to multi colored guard hairs around the neck, upper back and shoulders.

There is considerable evidence of dimorphism between the sexes, with males weighing between 7 and 13 pounds, and females between 3 and 7 pounds. Total lengths for males range from 35-47 inches, and females, 30-37 inches.

Fisher have large, wide feet with five toes on each foot and semi-retractable claws. This makes them well adapted for walking on snow, climbing trees and grasping and killing prey. They are capable of rotating their hind feet nearly 180º, which allows for a headfirst descent from trees. As with all members of the weasel family, both sexes have large anal scent glands which may be used to mark territories or attract potential mates.