The Murray cod (Maccullochella peelii) is a large Australian predatory freshwater fish of the genus Maccullochella in the family Percichthyidae. Although the species is called a cod in the vernacular, it is not related to the Northern Hemisphere marine cod (Gadus) species. The Murray cod is an important part of Australia's vertebrate wildlife—as an apex predator in the Murray-Darling River system—and also significant in Australia's human culture. The Murray cod is the largest exclusively freshwater fish in Australia, and one of the largest in the world. Other common names for Murray cod include cod, greenfish, goodoo, Mary River cod, Murray perch, ponde, pondi and Queensland freshwater cod.
The scientific name of Murray cod derives from an early Australian fish researcher with the surname McCulloch and the river from which the explorer Major Mitchell first scientifically described the species, the Peel River. This was for a number of years changed to M. peelii peelii to differentiate Murray cod from Mary River cod, which were designated as a subspecies of Murray cod. However, as of 2010, Mary River cod have been raised to full species status (M. mariensis), thus Murray cod have reverted simply to M. peelii.
Murray cod populations have declined severely since European colonisation of Australia due to a number of causes, including severe overfishing, river regulation, and habitat degradation and are now a listed threatened species. However, they once inhabited almost the entire Murray-Darling basin, Australia's largest river system, in very great numbers.
A long-lived fish, adult Murray cod are carnivorous and mainly eat other fish. The species exhibits a high degree of parental care for their eggs, which are spawned in the spring and are generally laid in hollow logs or on other hard surfaces. Murray cod are a popular angling target and aquaculture species. Often available through the aquarium trade, they are also a popular aquarium species in Australia.
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CongregatoryCongregatory animals tend to gather in large numbers in specific areas as breeding colonies, for feeding, or for resting.
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OviparousOviparous animals are female animals that lay their eggs, with little or no other embryonic development within the mother. This is the reproductive...
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SocialMi
MigratingAnimal migration is the relatively long-distance movement of individual animals, usually on a seasonal basis. It is the most common form of migrati...
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starts withThe Murray cod is a large grouper-like fish with a deep, elongated body that is round in cross section. It has a broad, scooped head, and a large mouth lined with pads of very small, needle-like teeth. The jaws of the Murray cod are equal, or the lower jaw protrudes slightly.
The spiny dorsal fin of Murray cod is moderate to low in height and is partially separated by a notch from the high, rounded soft dorsal fin. Soft dorsal, anal, and caudal (tail) fins are all large and rounded, and are dusky grey or black with distinct white edges. The large, rounded pectoral fins are usually similar in colour to the flanks. The pelvic fins are large, angular, and set forward of the pectoral fins. The leading white-coloured rays on the pelvic fins split into two trailing white filaments, while the pelvic fins themselves are usually a translucent white or cream, tending toward opacity in large fish.
Murray cod are white to cream on their ventral (belly) surfaces. Their backs and flanks are usually yellowish-green to green, overlain with heavy darker green, but occasionally brown or black, mottling. The effect is a marbled appearance sometimes reminiscent of a leopard's markings. Colouration is related to water clarity; colouration is intense in fish from clear water habitats. Small to medium-sized Murray cod from clear-water habitats often have striking and very distinct colouration. Very large fish tend towards a speckled grey-green colouration.
Murray cod are large fish, with adult fish regularly reaching 80–100 cm (31–39 in) in length. Murray cod are capable of growing well over 1 m (3.3 ft) in length and the largest on record was over 1.8 m (5.9 ft) and about 113 kg (249 lb) in weight. Large breeding fish are rare in most wild populations today due to overfishing.
The Murray cod is named after the Murray River, part of the Murray-Darling basin in eastern Australia, Australia's largest and most important river system, draining around 14% of the continent. The Murray cod's natural range encompasses virtually the whole Murray-Darling basin, particularly the lowland areas, and extending well into upland areas — to about 700 m (2,300 ft) elevation in the southern half of the basin and to about 1,000 m (3,300 ft) in the northern half of the basin.
Consequently, Murray cod inhabit a remarkably wide variety of habitats, from cool, clear, fast-flowing streams with riffle-and-pool structure and rocky substrates in upland areas to large, slow flowing, meandering rivers in the extensive alluvial lowland reaches of the Murray-Darling basin.Murray cod have died out in many of their upland habitats, particularly in the southern Murray-Darling basin, due to a combination of overfishing, siltation, dams and weirs blocking migration, pollution from arsenic-based sheep-dips, mining, and in some cases, introduced trout stockings, which causes competition between juvenile Murray cod and introduced trout species.Murray Cod have also been introduced into other drainage basins, such as the Cooper Basin in Queensland.
The Murray cod is the apex aquatic predator in the rivers of the Murray-Darling basin, and will eat almost anything smaller than itself and anything in its way, including finned fishes such as smaller Murray cod, golden perch, silver perch, bony bream, eel-tailed catfish, western carp gudgeon, and Australian smelt and introduced fish such as carp, goldfish, and redfin (English perch), as well as crustaceans such as yabbies, freshwater shrimp, and Murray crayfish. Fish compose the majority of the diet of mature Murray cod in lowland river and impoundment habitats, and that Murray cod are apex predators in these habitats. Murray cod have also been known to eat ducks, cormorants, freshwater turtles, water dragons, snakes, mice, and frogs. The observations of the recreational fishermen fishing for Murray cod with surface lures at night reveal that the popular description of Murray cod as a demersal ambush predator is only partially correct. While this behaviour is typical during the day, at night, Murray cod are active pelagic predators, venturing into shallow waters and frequently taking prey from the surface.
Murray cod reach sexual maturity between four and six years of age, generally five years. Sexual maturity in Murray cod is dependent on age. Therefore, roughly 70% of wild river Murray cod, with their slower growth rate, have reached sexual maturity by 50 cm (20 in) in length. Wild Murray cod in impoundments like Lake Mulwala, with their faster growth rates, do not reach sexual maturity until they are well over 60 cm (2.0 ft) in length. These data strongly indicate the 50-cm (20-in) size limit for Murray cod is inadequate and should be increased substantially to allow for a greater chance of reproduction before capture.
Large female Murray cod in the 15– to 35-kg (35– to 80-lb) range are the most important breeders because they produce the most eggs and for other reasons; large females in most fish species are also important because they produce larger larvae with larger yolk sacs, and are also more experienced breeders that display optimal breeding behaviours. Such large females may also have valuable, successful genes to pass on. All of these factors mean the spawnings of large female fish have far higher larval survival rates and make far greater reproductive contributions than the spawnings of small female fish. Not surprisingly, there is no truth to claim made by some recreational fishers that "large Murray cod don't breed".
Female Murray cod, upon first reaching sexual maturity, have egg counts of no more than 10,000. Very large female Murray cod can have egg counts as high as 80,000–90,000, although a recent, very large 33-kg specimen yielded an egg count of 110,000 viable eggs. Egg counts in female Murray cod of all sizes are relatively low compared to many fish species.
Murray cod spawn in spring, cued by rising water temperatures and increasing photoperiod (daylight length). Initially, fish biologists working with Murray cod considered spring floods and temperatures of 20–21 °C (68–70 °F) to be necessary and that spring flooding is critical for successful recruitment (i.e. survival to juvenile stages) of young cod by providing an influx of pelagic zooplankton and early life-stage macroinvertebrates off the flood plain into the main river channel for first feeding, but more recent research has shown Murray cod breed annually, with or without spring floods, and at temperatures as low as 15 °C (59 °F). Additionally, recent research has shown abundant epibenthic/epiphytic (bottom dwelling/edge clinging) prey in unflooded lowland rivers, traits in Murray cod larvae that should allow survival in a variety of challenging conditions, and a significant proportion of Murray cod larvae feeding successfully in unflooded rivers.
Latest research has also shown that Murray cod in fact live their entire lifecycle within the main channel of the stream. Earlier ideas that Murray cod spawn on floodplains, or the larvae feed on floodplains, are incorrect. Murray cod breed in the main river channel or, in times of spring flood, the inundated upper portion of the main channel and tributary channels, but not on floodplains. Murray cod larvae feed within the main river channel or, in times of spring flood, on the inundated upper portion of the main channel and the channel/floodplain boundary, but not on the floodplain.
Spawning is preceded by significant upstream migrations if high spring flows or floods allow. Radio-tracked Murray cod in the Murray River have migrated up to 120 km (75 mi) upstream to spawn, before returning to exactly the same snag from where they departed, an unusual homing behaviour in a freshwater fish. Decades of observations by recreational and commercial fishermen suggest such spring spawning migrations are common across the Murray cod's geographical range. Spawning is initiated by pairing up and courtship rituals. During the courtship ritual a spawning site is selected and cleaned — hard surfaces such as rocks in upland rivers and impoundments, and logs and occasionally clay banks in lowland rivers, at a depth of 2–3 metres (6.6–9.8 ft), are selected. The female lays the large adhesive eggs as a mat on the spawning surface, which the male fertilises. The female then leaves the spawning site. The male remains to guard the eggs during incubation, which takes six to 10 days (depending on water temperature), and to guard the hatched larvae for a further week or so until they disperse. Larvae disperse from the nest site by drifting in river currents at night, and continue this behaviour around four to seven days. During this dispersal process, larvae simultaneously absorb the remainder of their yolk sac and begin to feed on pelagic zooplankton, small, early life-stage macroinvertebrates and epibenthic/epiphytic (bottom dwelling/edge clinging) microinvertebrates. It may be that Murray cod are the first freshwater fish identified as having long-term pair-bonding in its repertoire of mating strategies in the wild.
The relationship between river flows and Murray cod recruitment are more complex than first thought, and in less regulated rivers, Murray cod may be able to recruit under a range of conditions including stable low flows. (Significant recruitment of Murray cod in low-flow conditions in less regulated lowland rivers has now been proven.) This information also suggests that nonriver-regulation-related causes of degradation are playing a larger role in the survival and recruitment of Murray cod larvae than first thought; competition from extremely large numbers of invasive carp larvae are negatively affecting the survival and recruitment of Murray cod larvae to a much greater degree than first thought; and that decades of overfishing is playing a far larger role in the current state of Murray cod stocks, through depletion of spawning adults, than first thought.
These findings do not mean that river regulation and water extraction have not had adverse effects on fish stocks. Rather, river regulation has been a major factor in the decline of Murray cod and other native fish. Thermal pollution is also a major problem, evidence indicates strong Murray cod recruitment events (which may be important for sustaining Murray cod populations over the long term) can result from spring flooding, and the health of Australian lowland river ecosystems generally rely on periodic spring flooding. Also, due to the regulation of most of the rivers in the Murray-Darling River system, mainly for irrigation purposes, only exceptional spring floods manage to "break free". The long-term viability of wild Murray cod, other native fish species and river ecosystems, in the face of this fact, are of great concern.
Since 3 July 2003 and as of August 2023, the Murray cod is listed as a vulnerable species under the EPBC Act (Environment Protection and Biodiversity Conservation Act 1999). It is listed as a species of Least Concern on the IUCN Red List of Threatened Species, but under state legislation in both South Australia and Victoria, it is an endangered species.
A study published in Biological Conservation in March 2023 listed 23 species which the authors considered to no longer meet the criteria as threatened species under the EPBC Act, including the Murray cod. The team, led by John Woinarski of Charles Darwin University looked at all species listed as threatened under the act in 2000 and 2022. The Murray cod was the only fish on the list, and the reason for their assessment was given as "Actual recovery over the period 2000–2022, from long period of decline".
State government fisheries departments support Murray cod populations by stocking with hatchery-bred fish, especially in man-made lakes. Important issues affecting restoration of cod populations, such as the need for spring floods and excessive angler take, are slowly being acknowledged but are yet to be definitely addressed. Other concerns such as the stocking of Murray cod in areas where trout cod (M. macquariensis) are recovering encourages hybridisation and needs consideration for future restocking programs.
Murray cod play a very important role in the mythology of many Aboriginal tribes in the Murray-Darling basin, and for some tribes, particularly those living along the Murray River, Murray cod were the icon species. The myths of these tribes describe the creation of the Murray River by a gigantic Murray cod fleeing down a small creek to escape from a renowned hunter. In these myths, the fleeing Murray cod enlarges the river and the beating of its tail create the bends in it. The cod is eventually speared near the terminus of the Murray River, chopped into pieces, and the pieces thrown back into the river. The pieces become all the other fish species of the river. The cod's head is kept intact, told to "keep being Murray cod", and also thrown back into the river.
Social animals are those animals that interact highly with other animals, usually of their own species (conspecifics), to the point of having a rec...