Boreogadus saida, known as the polar cod or as the Arctic cod, is a fish of the cod family Gadidae, related to the true cod (genus Gadus). Another fish species for which both the common names Arctic cod and polar cod are used is Arctogadus glacialis.
Description
alt=The image shows a close-up view of five Boreogadus saida lying horizontally in a pile within a plastic basket with orange slats. Each fish has a number label placed above it, ranging from 1 to 5, helping distinguish them from one another. These fish appear similar in shape and color, with silvery bodies, large eyes, and prominent mouths. However, the top three fish, labelled 1 to 3, are slightly darker in color. The bottom two fish, labelled 4 to 5, are slightly lighter in color and smaller.|thumb|Dark (1,2,3) and Light (4,5) [[Polymorphism (biology)|morphotypes described by Inuit fishers
Arctic cod are frequently misidentified as polar cod (Arctogadus glacialis) during their larval and early juvenile stages. The species can be differentiated through the analysis of otoliths or molecular data.
Arctic cod grow to an average length of 25 cm (9.8 in), and a maximum length of . (beyond 84°N) with a circumpolar distribution spanning the entire North Polar Basin above Russia, Alaska, Canada, and Greenland. More specifically, in the Arctic Ocean, Bering Sea, Chukchi Sea, Beaufort Sea, Hudson Bay, Baffin Bay, Greenland Sea, Barents Sea, Kara Sea, Laptev Sea and the Eastern Siberian Sea. In the Canadian Arctic, Arctic cod will separate vertically in the water column by size, with younger fish in the upper of the water column, and juvenile and immature fish below .
Arctic cod can also be found in dense schools near glacial fronts and polynyas. The key adaptation that allow for a decrease in their freezing point lies in their blood: specifically, high molecular mass antifreeze glycoproteins. These special proteins decrease the freezing point of ice, preventing the formation of ice crystals in the blood. This adaptation, shared with Antarctic notothenioid fish, help the cod retain vital antifreeze glycoproteins in their blood. It also prevents the fish from experiencing osmotic stress, as the high salt content of the Arctic Oceans draws water out of their bodies.]]
Arctic cod are a keystone species in Arctic marine food webs.
Arctic cod are locally dominant prey for Atlantic cod, Arctic char, and Greenland halibut. They are also prey for seabirds, specifically the thick-billed murre, black guillemot, common murre, northern fulmar, black-legged kittiwake, ivory gull, and glaucous gull. Arctic cod are the primary food source for species endemic to the Arctic, namely narwhals, belugas, ringed seals, and harp seals. Arctic cod larvae feed on eggs, nauplii, and copepods.]]
The development and viability of Arctic cod eggs depend heavily on temperature. Eggs develop normally between ; however, hatching success severely declines above .
Fishery
thumb|215x215px|Arctic cod frozen at sea from a Russian vessel. Typically 10 or 16 kg net weight.thumb|296x296px|Uummannaq fishers preparing their [[Longline fishing|longlines onboard dinghies used for Greenland halibut fishing, July 2022. The same dinghies are used for Arctic cod fishing, with nets instead of longlines. Climate models predict that ice algae populations will increase because of decreases in ice thickness, allowing more light for primary production. This change will be favorable for young Arctic cod, but inter-annual variability in primary production might lead to different long-term outcomes.
Less sea ice will lead to increased anthropogenic activities in the Arctic, especially commercial shipping. Experimental studies have shown that Arctic cod respond to noise pollution from moving shipping vessels by retreating to areas with lower noise levels. Arctic cod also tend to aggregate in the presence of vessel noise. Increased usage of shipping lanes through the Arctic will likely fragment habitat for Arctic cod. With shipping comes the possibility of oil spills, which will also affect Arctic cod as they lack glomeruli to filter out toxins from their blood.