The Mary River cod (''Maccullochella mariensis'') is a

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

of temperate perch native to the coastal Mary River system of southern

Queensland Queensland ( , commonly abbreviated as Qld) is a States and territories of Australia, state in northeastern Australia, and is the second-largest and third-most populous state in Australia. It is bordered by the Northern Territory, South Austr ...

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

. Mary River cod are one of Australia's most endangered freshwater fishes and are notable for being the most northerly of the four '' Maccullochella'' cods found or once found in coastal river systems of eastern Australia. The endangered status of the fish was one of the reasons that the Traveston Crossing Dam was not able to be built. The species is very territorial, staying in the same spot for 98% of the time, leaving only to feed and breed.

Description

The Mary River cod is a large fish recorded up to almost 40 kg and 120 cm in the early years of European settlement, but now are mostly less than 5 kg and 70 cm. Very similar in appearance to

Murray cod The Murray cod (''Maccullochella peelii'') is a large Australian predatory freshwater fish of the genus '' Maccullochella'' in the family Percichthyidae.Dianne J. Bray & Vanessa J. Thompson (2011Murray Cod, Maccullochella peelii Fishes of Au ...

and eastern freshwater cod, they are striking looking, golden-yellow to dark green or brown, deep-bodied fish with dark green to black mottling. Curiously, Mary River cod have a slightly shorter, thicker caudal peduncle (tail wrist) than the other cod species.

Conservation

The Mary River Cod is listed as

Endangered An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching, inv ...

under the

Environment Protection and Biodiversity Conservation Act 1999 The ''Environment Protection and Biodiversity Conservation Act 1999'' (Cth) is an Act of the Parliament of Australia that provides a framework for protection of the Australian environment, including its biodiversity and its natural and cult ...

and is estimated to only occur in less than 30% of its historic range. Incredibly abundant at the time of the first European settlement, Mary River Cod were grossly

overfished Overfishing is the removal of a species of fish (i.e. fishing) from a body of water at a rate greater than that the species can replenish its population naturally (i.e. the overexploitation of the fishery's existing fish stock), resulting in the ...

with nets, lines, and

explosives An explosive (or explosive material) is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An exp ...

by the early European settlers and, as with other ''Maccullochella'' cods, were even used as pig feed. This

overfishing Overfishing is the removal of a species of fish (i.e. fishing) from a body of water at a rate greater than that the species can replenish its population naturally (i.e. the overexploitation of the fishery's existing Fish stocks, fish stock), resu ...

, combined with the massive

siltation Siltation is water pollution caused by particulate terrestrial clastic material, with a particle size dominated by silt or clay. It refers both to the increased concentration of suspended sediments and to the increased accumulation (temporary o ...

of their habitats by

land clearing Deforestation or forest clearance is the removal and destruction of a forest or stand of trees from land that is then converted to non-forest use. Deforestation can involve conversion of forest land to farms, ranches, or urban use. About ...

, destruction of riparian vegetation and cattle trampling river banks, and

dam A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use, aqua ...

s and weirs blocking migration, rapidly caught up with this large, slow-growing, long-lived ''Maccullochella'' cod species, as it has with all its close relatives. It is estimated that just 600 individuals survived in the wild in the 1980s. Outside of a few stocked Queensland impoundments- upstream of the walls of Cressbrook, Hinze, Maroon, Moogerah, North Pine, Somerset, and Wivenhoe Dams and lakes Dyer (Bill Gunn dam) and Clarendon- the fish is a no-take species, and any caught should be carefully released. A strict bag limit of one fish with a minimum size of 50 cm applies to the stocked impoundments.

Classification

Taxonomically, the Mary River cod was originally described as a subspecies of the Murray cod, ''Maccullochella peelii'' based on studies of muscle proteins and enzymes. As of 2010, after studies of mitochondrial and nuclear DNA, the Mary River cod has been raised to full species status.Nock C.J., Elphinstone M.S., Rowland S.J. and Baverstock, P.R. (2010). Phylogenetics and revised taxonomy of the Australianfreshwater cod genus, ''Maccullochella'' (Percichthyidae). ''Marine and Freshwater Research'' 61: 980–991. This research reveals the Mary River cod's closest relative is the eastern freshwater cod (''Maccullochella ikei'') of the Clarence River system.

References

* Rowland, S.J. (1993). ''Maccullochella ikei'', an endangered species of freshwater cod (Pisces: Percichthyidae) from the Clarence River System, NSW, and ''M.peelii mariensis'', a new subspecies from the Mary River System, QLD. ''Records of the Australian Museum'' 45: 121-145. * Simpson, R.R. and Mapleston, A.J. (2002). Movements and Habitat Use by the Endangered Australian Freshwater Mary River cod, ''Maccullochella peelii mariensis''. ''Environmental Biology of Fishes'' 65: 401–410. {{Taxonbar, from=Q6780612 Mary River cod Mary River (Queensland) Freshwater fish of Queensland Mary River cod