The Brisbane River cod was a unique form of Maccullochella

Maccullochella

Maccullochella is a genus of large Australian predatory freshwater fish within the Percichthyidae family. The Maccullochella genus was named after an early Australian fish researcher with the surname McCulloch....

cod that occurred naturally in the Brisbane River

Brisbane River

The Brisbane River is the longest river in south east Queensland, Australia, and flows through the city of Brisbane, before emptying into Moreton Bay. John Oxley was the first European to explore the river who named it after the Governor of New South Wales, Thomas Brisbane in 1823...

 system, an east coast river system in south east Queensland

Queensland

Queensland is a state of Australia, occupying the north-eastern section of the mainland continent. It is bordered by the Northern Territory, South Australia and New South Wales to the west, south-west and south respectively. To the east, Queensland is bordered by the Coral Sea and Pacific Ocean...

, Australia

Australia

Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

. Their exact taxonomic status is not known, but based on several genetic studies it is suspected that Brisbane River Cod were a species intermediate between Eastern Freshwater Cod

Eastern freshwater cod

Eastern freshwater cod, Maccullochella ikei, also known as eastern cod, are a large and striking predatory freshwater fish of the Maccullochella genus and the Percichthyidae family, that occur in the coastal Clarence River system of north-eastern New South Wales...

 (Maccullochella ikei) of the Clarence River

Clarence River (New South Wales)

The Clarence River is situated in northeastern New South Wales, Australia. The river originates on the watershed that marks the Queensland border. After flowing south and northeast for 394 km it then empties into the Pacific Ocean at Iluka/Yamba. On its journey it passes through the towns of...

 and Richmond River systems in northern New South Wales and Mary River Cod

Mary River cod

Mary River cod are a Maccullochella cod found in the coastal Mary River system of southern Queensland, Australia...

 of the Mary River

Mary River (Queensland)

The Mary River is a river system in South East Queensland, Australia. The river rises at Booroobin in the Sunshine Coast hinterland, west of Landsborough...

 in central Queensland.

All naturally occurring Maccullochella

Maccullochella

Maccullochella is a genus of large Australian predatory freshwater fish within the Percichthyidae family. The Maccullochella genus was named after an early Australian fish researcher with the surname McCulloch....

cod in east coast drainages ultimately originate from Murray cod

Murray Cod

The Murray cod is a large Australian predatory freshwater fish of the Maccullochella genus and the Percichthyidae family. Although the species is a called cod in the vernacular, it is not related to the northern hemisphere marine cod species...

, Maccullochella peelii that entered an east coast river system, likely the Clarence, via a natural river capture

River capture

Stream capture, river capture, or stream piracy is a geomorphological phenomenon occurring when a stream or river drainage system or watershed is diverted from its own bed, and flows instead down the bed of a neighbouring stream...

 event somewhere between 0.62 and 1.62 million years ago (mean estimate 1.1 million years ago), as estimated by DNA

DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

 divergence rates.

Brisbane River cod are extinct, from overfishing

Overfishing

Overfishing occurs when fishing activities reduce fish stocks below an acceptable level. This can occur in any body of water from a pond to the oceans....

, habitat destruction

Habitat destruction

Habitat destruction is the process in which natural habitat is rendered functionally unable to support the species present. In this process, the organisms that previously used the site are displaced or destroyed, reducing biodiversity. Habitat destruction by human activity mainly for the purpose of...

 and siltation

Siltation

Siltation is the pollution of water by fine 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 of fine sediments on bottoms where they are undesirable...

, and whole-of-catchment scale bushfires and ash fish kill

Fish kill

The term fish kill, known also as fish die-off and as fish mortality, is a localized die-off of fish populations which may also be associated with more generalised mortality of aquatic life...

s in the 1930s.

The Brisbane River has now been restocked with Mary River cod

Mary River cod

Mary River cod are a Maccullochella cod found in the coastal Mary River system of southern Queensland, Australia...

from the Mary River system.