The Alaska blackfish, Dallia pectoralis, is a fish that grows to 7 inches (180 mm) in length. It is elongate and cylindrical, with a dark olive-brown coloration. Four to six dark blotches run vertically along the sides, and the belly is white. The fins have reddish-brown speckles. Once thought to be an herbivore, its primary diet is midges and mosquito insect larvae. Alaska blackfish are found in swamps, ponds, lakes, and streams with vegetation for cover, in tundra and forested locations not far inland. Their range includes Alaska and the Bering Sea islands. Alaska Natives once ate these fish and fed them to their dogs, catching them in the fall and freezing them for use over winter.
The hardiness of the Alaska blackfish is of mythical proportions, including tales of reviving fish after they are frozen solid. The fish survive the cold winters by moving to a depth of 7-8 metres (23-26 ft) when the surface becomes solid ice. Large gills protected by gill covers help them to survive the winters where the water temperatures drop to 0 ºC (32 ºF). Though the Alaskan blackfish can be supercooled for short periods at temperatures as low as -20 ºC (-4 ºF) in controlled environments without contact with ice crystals, no Alaska blackfish has ever survived for even as much as an hour under these freezing conditions. Freezing any part of the body results in necrosis.