Arctic cod, Boreogadus saida.

The arctic cod is a slender fish that grows to a maximum length of 30 cm, with populations in the North having a larger body size than those in the South. For example, off the coast of northern Labrador, the arctic cod is typically 25 to 30 cm, while individuals off eastern Newfoundland rarely exceed 18 cm in length. Although this species has a similar appearance to other codfishes, it is easily recognized by its slender body, deeply forked tail, projecting mouth, and small chin barbels. It is plainly coloured, brownish, spotted above, and silvery on the belly. Its typical, cod-like fins are almost black, with a pale streak at the base.

The arctic cod has a circumpolar distribution and occurs farther north than any other marine fish. Its vast distribution spans the Arctic seas off northern Russia, Alaska, Canada, and Greenland. In Canada, it frequents the Beaufort Sea, the Arctic Archipelago, Hudson Bay, Baffin Bay, and along the coasts of Labrador and Newfoundland. Arctic cod are most common at the water's surface, but they also occur at depths below 900 metres. In ice-free waters, this fish forms gigantic schools, but when under the ice, it prefers a rough under-surface where it can hide in the cracks.

In the polar waters of northern Canada, arctic cod spawn each year in the late fall and early winter. Amazingly, up to 10% of a male's body weight consists of gonads! At spawning time, females produce from 9000 to 21,000 eggs that are 1.5 mm in diameter. However, little is known about its mating behaviour.

The arctic cod favours temperatures below 4°C and it is one of the few fish that thrives in temperatures below 0°C. Antifreeze proteins in its blood are one adaptation responsible for this ability. With its widespread distribution and abundance, this fish is a key component of Arctic food webs and is a primary food source for narwhals, belugas, ringed seals, and seabirds. It is also preyed upon by other fishes such as arctic charr, Greenland halibut, and Atlantic salmon. Arctic cod are the main consumers of plankton in the upper water column (unlike their relative, the Atlantic cod, which feeds on the bottom). As they grow, they graduate from a diet of copepods to a diet of marine worms, adult copepods, shrimp and may even become cannibalistic. With a usual lifespan of no more than six years, they are relatively short-lived. The age of an arctic cod can be determined by counting annual rings of growth in its otoliths, the tiny bones in their inner ear, much like counting the rings of a tree.

The arctic cod is not commercially harvested in Canada, but is considered an excellent table fish in Russia. Offshore fishing boats from Russia often haul in large numbers of these fish as a by-catch of the capelin fishery.