Murray cod was originally distributed trhoughout the Murray-Darling river system in southeastern Australia, except for the upper reaches of the southern tributaries. Murray cod have been widely translocated to waters within their natural range and introduced to waters outside it throughout this and last century. In 1990, Murray cod have been introduced to the Cooper Creek system in central Australia (Ref. 27499). Very few of the earlier stocked populations have survived (Ref. 27446), but some are still present in many farm dams and water supply reservoirs.

Stock structure: It has been demonstrated that populations of Murray cod, Maccullochella peelii, from the Murray-Darling basin were genetically divergent from Murray cod populations occurring in two coastal rivers of eastern Australia (Ref. 27444).

Commercial fishery: The Aborigines were the first to fish for Murray cod, using traps, spears, nets and poisons. Early European explorers were quick to realise its value. The first commercial inland fishery began on the Murray-Darling river system in the mid to late 1800s. Murray cod dominated the early catches, with records (Ref. 27446) showing that it comprised 75% of the river fish available at the Melbourne Wholesale Fish market in 1900. Total inland catch declined from a peak in 1918, yet in 1940-51 Murray cod still comprised 42-65% of the total inland catch in New South Wales. It is now less than 10% of this catch (Ref. 27498). In South Australia Murray cod made up only 0.4% of the State's inland catch by 1988-89.

As of 1993, the commercial fishery for Murray cod is concentrated on the lower reaches of the Murray and Murrumbidgee rivers, from Deniliquin to the South Australian border, the Edward and Wakool rivers and Lake Victoria. Gillnets and drum nets are the main nets used. Drum nets are set close to the banks in flowing water with their opening facing downstream. Gillnets are set in still waters and generally left overnight (Ref. 27500).

All Murray cod caught are for domestic consumption. They are sold as wet, gutted fish in local markets and through the fish markets in Melbourne, Adelaide and Sydney.

Recreational fishery: Murray cod is a highly valued recreational species because of its size, its value for sport and its edibility. Recreational fishing for Murray cod is concentrated around the major towns on the lower Murray, Murrumbidgee and Lachlan rivers and the Darling River (downstream from Menindee) and impoundments on or near these river sections (Ref. 27447). Murray cod are also keenly sought in the Barwon, Macintyre and other northern rivers.

Anglers targeting Murray cod have most success using set lines with live bait such as small fish, yabbies (Cherax species) and 'bardi grubs' (burrowing moth and beetle larvae - Lepidoptera). Murray cod are also taken using rod-and-line with artificial lures (Ref. 27498). The recreational catch of Murray cod probably now surpasses the commercial catch. Although individuals exceeding 50 kg are rarely taken, small numbers of fish between 20 kg and 40 kg are regularly caught by experienced anglers. According to records of the Australian Anglers Association the largest fish taken weighed 50.4 kg, and was caught in South Australia in 1967.

Resource status: Heavy commercial fishing pressure in the period up to the 1930s saw the decline of Murray cod in the inland catch. In the mid-1930s catches declined to levels unprofitable for large-scale operators. Catches of Murray cod increased again between 1940 and 1951, but declined in following years, stabilising around the current low levels in the 1960s (Ref. 27446).

While much of the decline in Murray cod numbers up until the 1930s can be attributed to over-fishing, environmental changes such as those caused by removal of snags or by the construction dams, levee banks, and high level weirs throughout the Murray-Darling river system have undoubtedly had a major effect since the 1950s. These constructions have altered the natural flow and temperature regimes of the river and reduced the incidence of seasonal flooding. Flooding promotes the production of zooplankton on which Murray cod larvae feed, and its suppression has probably reduced larval recruitment and hence Murray cod numbers. Poor juvenile recruitment is probably the main reason for the continued decline in the Murray cod populations within the river system (Ref. 27446).

Another possible factor contributing to the decline of Murray cod in the Murray-Darling river system is the introduced fish, redfin, Perca fluviatilis. The diets of these 2 fish species overlap extensively and it is also possible that juvenile redfin prey on cod larvae. Redfin also spawn earlier in water temperatures of around 12°C. As a result there is competition for resources, particularly during drought periods (Ref. 27446).

Murray cod are now classified as a vulnerable species in Victoria (that is, a species that has undergone a substantial reduction in range and abundance and that is likely to become an endangered or threatened species if current trends continue) (Ref. 6987). Murray cod fishing is now banned in South Australian waters.