The story of the Murray Cod mirrors that of most Australian endangered species. Because of its abundance, the cod was commercially fished from the early years of European settlement.
Changes to its natural habitat and competition from introduced fish have also had a big impact on cod numbers.
In 1883, commercial fisheries sent 147,000kg of cod from the Murray River town of Moama to Melbourne for sale. By the 1920s cod were in short supply and the commercial fishing industry stopped.
The fish was an important source of food to Indigenous people. Its cultural significance differs depending on the Indigenous nation and the area inhabited.
One of the most common stories comes from Ngarrindjeri Country, close to the mouth of the Murray in South Australia. It concerns Ponde or Pondi, a giant ancestral cod. Ngurunderi, a great hunter, chased Ponde. Ponde’s thrashes and gyrations while trying to escape formed the bends and billabongs of the Murray.
Ngurunderi speared the fish at Lake Alexandrina, cut it up and threw some of the parts into the water. These then became other Murray River fish species. One part of Ponde, which was also thrown into the water, remained the Murray cod.
Murray Cod appearance
The Murray Cod is Australia’s largest freshwater fish. The biggest recorded was 1.8m long and weighed 113kg!
The cod’s size depends on its habitat, with those living in smaller waterways reaching at least 60cm and between 3kg to 4kg. In larger waterways they grow to 100 cm or more and weigh up to 20kg.
The cod is one of Australia’s prettiest fish. It's white underneath and yellowish-green to green on its back. This is overlaid with darker green mottling, which gives the fish leopard-like spots.
It's one of four sub-species in the genus Maccullochella. The others are the Mary River Cod, the Trout Cod, the Eastern Freshwater Cod.
None of these are related to the northern hemisphere cod, which is part of the Gadus species.
Where do Murray Cod live?
The Murray Cod inhabits the Murray-Darling basin, which spreads through New South Wales, South Australia and Victoria. Thousands of interconnected creeks and rivers run through the basin. Some of the basin’s major rivers are the Murray, Darling, Warrego, Murrumbidgee, Lachlan, Goulburn, Campaspe, Mitta Mitta and Loddon.
Below the basin is a complex system of aquifers and groundwater. Most of the waterways eventually connect to the Murray River. The cod lives in warm water habitats ranging from clear, rocky streams to slow-flowing turbid rivers and billabongs.
Murray Cod behaviour
Also known as 'pigs of the waterways' Murray Cod are very aggressive and highly territorial. They'll also eat almost anything that gets in their way.
Their diet is mostly other fish, including introduced species such as perch, juvenile carp and goldfish. It's also been known to eat ducks, cormorants, freshwater turtles, water dragons, snakes, mice, and frogs.
A Murray Cod can live for more than 50 years, which gives it a greater chance of reproducing despite extreme weather events such as droughts.
The cod reaches sexual maturity at between four and six years old. It moves upstream to spawn, often travelling as far as 120km. This usually occurs in late winter or early spring when river levels are high.
Eggs are adhesive and placed on a hard surface such as logs, rocks or clay banks. Once the eggs are laid, the fish will move back downstream, usually to exactly the same place it began. The male guards the eggs, which hatch between 5 and 13 days after being laid.
Threats to Murray Cod
Murray Cod, once listed as 'Critically Endangered' on the International Union for Conservation of Nature's Red List have been upgraded to 'Of Least Concern' as numbers increase. They're still listed as 'Vulnerable' under the Environmental Protection of Biodiversity and Conservation Act. According to some estimates, cod numbers have been as low as 10% of those that existed before European settlement.
The cod has moved from being considered as a plentiful source of food to an important but threatened part of the Murray Darling ecosystem.
What’s Bush Heritage doing?
Our efforts to protect the cod centre on Scottsdale Reserve, just 40km from Canberra. We acquired Scottsdale, on the upper reaches of the Murrumbidgee, in 2006. The Murrumbidgee forms the western and northern boundaries of the property for a distance of about 4.5km.
Bush Heritage is involved in a regional partnership that aims to improve water quality and habitat along a 100km stretch of the river called the Upper Murrumbidgee Demonstration Reach. Amongst the projects this group has undertaken, is work focused on European carp control.
Since the carp was introduced about 150 years ago, it's become a pest. More than 96 out of every 100 fish caught in the demonstration reach is a carp. The effects of carp on native fish populations are not well understood. It's thought, however, that high carp numbers are preventing the recovery of native fish such as the nationally threatened Murray Cod, Macquarie Perch and Trout Cod, as well as locally (ACT) threatened Murray River Crayfish, Silver Perch and Two‑spined Blackfish.
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