--- title: "Atlantic Cod (Gadus morhua) | AnimalTracks.wiki" description: "A big bottom predator that lost an immune pathway jawed vertebrates normally keep." image: "https://animaltracks.wiki/images/animals/atlantic-cod-1.webp" published: "2026-10-11" updated: "2026-10-11" --- # Atlantic Cod (*Gadus morhua*) > **Status**: Checked against 5 sources, listed under Sources below. > **Tagline**: A big bottom predator that lost an immune pathway jawed vertebrates normally keep. > **Soundtrack Vibe**: 90s Riot Grrrl & Grunge // Sleater-Kinney, "Dig Me Out" > **Soundtrack Links**: [Spotify](https://open.spotify.com/track/1YdCuoPvDDVyHa3YomPb1B) > **Vibe Match**: The Atlantic cod has lost the genes for MHC II, a part of the immune system jawed vertebrates normally keep, and carries a highly expanded set of MHC I genes instead. Sleater-Kinney have no bass player, so on Dig Me Out a guitar tuned low covers the missing part. ## Biological Superpowers & Stats - **Taxonomy**: *Gadus morhua* - **Danger Level**: Low - **Conservation Status**: Vulnerable ([IUCN Red List](https://doi.org/10.2305/iucn.uk.1996.rlts.t8784a12931575.en)) - **Superpower**: Has lost the genes for MHC II, a standard part of the jawed-vertebrate immune system, but carries a highly expanded set of MHC I genes - **Habitat**: Cold North Atlantic and Arctic seas, from Greenland and Iceland to the Bay of Biscay and, on the American side, south to Cape Hatteras - **Diet**: Invertebrates and fish, including young cod - **Tags**: fish, ocean, predator ## Natural History & Behavior ## A fish with a hole in its immune system In 2011, researchers sequenced the cod's genome and found something strange. The genes for MHC II, CD4 and invariant chain were simply missing. Together they run a pathway of the adaptive immune system, and that pathway is a standard feature across jawed vertebrates. What the cod does have is a highly expanded number of MHC I genes and an unusual mix of Toll-like receptor families. > **Missing genes** > The cod has no genes for MHC II, CD4 or invariant chain, yet in natural conditions it is not especially prone to disease. The authors take the extra MHC I genes and the odd receptor mix as signs that the cod evolved compensating mechanisms in both adaptive and innate immunity. ## Heavy body, one whisker The cod is a thick, heavy fish with a big head, a blunt nose and a single whisker, called a barbel, hanging from its chin like a catfish's. Colour runs from yellowish-green to red and olive, and an individual can change colour readily. FishBase lists a maximum length of 200 cm, a common length of 100 cm and a maximum published weight of 96 kg. The oldest cod on its record was 25 years old. ## Cold water, hungry at dusk The cod lives across the North Atlantic and Arctic, from Ungava Bay in Canada south to Cape Hatteras, North Carolina, around Greenland and Iceland, and across to the Barents Sea and the Bay of Biscay. It is found from the shoreline to 600 m, usually at 150 to 200 m, in water from 0 to 15 degrees C. Young cod prefer shallow water with seagrass, gravel or boulders to shelter in. Adults are usually found in deeper, colder water. By day they school about 30 to 80 m above the bottom, then spread out at night to feed on invertebrates and fish, including young cod. Cod mostly stay within the area of their own stock, and trips over 200 km are rare. ## Millions of eggs, then a crash Cod spawn in winter and early spring. FishBase gives 2.5 million eggs for a 5 kg female and a record of 9 million for a 34 kg female. Off southern Labrador and eastern Newfoundland, the populations known as northern cod crashed in the late 1980s and early 1990s, one of the worst collapses fisheries have seen. Canada closed directed fishing for northern cod in July 1992, and in 2004 the authors reported the populations still historically low after a decade-long offshore moratorium. Up to the moratorium, the fish had been maturing at earlier ages and smaller sizes, a shift the authors suggest is fisheries-induced evolution. The IUCN Red List rates the species Vulnerable, in an assessment made in 1996, which FishBase still lists as the Red List status. ## Frequently Asked Questions ### How big does an Atlantic cod get? The longest on record reached 200 cm and the heaviest published weight is 96 kg, but 100 cm is a more common length. *(Source: [FishBase]())* ### How long can a cod live? The oldest age reported for the species is 25 years. *(Source: [FishBase]())* ### Does a cod really lack part of its immune system? Yes. Its genome has lost MHC II, a conserved part of adaptive immunity in jawed vertebrates, along with CD4 and invariant chain, which that pathway needs. The authors still found it not exceptionally prone to disease in natural conditions. *(Source: [Star et al. 2011]())* ## Sources 1. [Sobel (1996). Gadus morhua. The IUCN Red List of Threatened Species 1996: e.T8784A12931575.]() 2. [Star et al. (2011). The genome sequence of Atlantic cod reveals a unique immune system. Nature.]() 3. [Olsen et al. (2004). Maturation trends indicative of rapid evolution preceded the collapse of northern cod. Nature.]() 4. [Gadus morhua, Atlantic cod. FishBase.]() 5. [Atlantic Cod. NOAA Fisheries.]() *Published October 11, 2026. 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