Alaska blackfish

The Alaska blackfish is a species of freshwater fish in the family Esocidae, native to Arctic wetlands of Alaska, Siberia and islands in the Bering Sea. It is a small fish, averaging about 108 millimeters in length though some individuals reach 330 millimeters, with a large posterior dorsal fin, large lobed pectoral fins, and dark green to brown coloring with pale blotches. It lives in heavily vegetated swamps, ponds, rivers and lakes. The species has two notable adaptations to its harsh environment: it can breathe atmospheric oxygen through a modified, heavily vascularized esophagus, and it has been reported to survive exposure to temperatures as low as minus 20 degrees Celsius for 40 minutes.