Murray Cod

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ashdavid

In Search Of Better Water Quality
Mar 27, 2005
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I have a request. Please put the Murray Cod in the species profiles. It is a great looking aquarium fish if you have a big enough tank. I should mention it has been known to grow to 250lbs.
 

Nuriel

AC Members
Sep 6, 2004
519
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Seattle, Wa. USA
www.43things.com
why put a fish in the profies that very few will be able to house? if it gets to 250 doesnt sound like it needs a big tank, sounds like it needs a public aqaurium or something!!!!
wow, now i see they have some info on keeping these beasts captive at the bottom of this article, geezus i never would but i bet they are awesome to behold.

Scientific Name

Maccullochella peelii peelii
Other Common Names

cod, codfish, goodoo
Size

Commonly to about 60 cm, 3 to 4 Kg, occasionally 1 m, 28 Kg.
Maximum Recorded size:1.83 m, 113 Kg (6 ft, 250 lbs)

Photo of a Murray cod

Description

A large, elongate, deep bodied fish with small eyes and a short, rounded, depressed snout with a distinctly concave profile. Lower jaw protruding, or jaws equal in some (usually smaller) specimens. Low spiny dorsal fin and large, rounded soft dorsal, caudal (tail) and anal fins.

A light green to dark green colour on the back and sides that is overlain with heavy mottlings in dark green or black. Undersides are a creamy white. Soft dorsal, caudal and anal fins greyish to black in colour with striking white edges. Colouration of Murray cod is dramatic and often strikingly vivid and beautiful in small to medium sized specimens from clear water. Colouration of Murray cod in very turbid water however, tends to be washed out. Some very large Murray cod have a speckled green-grey appearance.

Larger Murray cod increase in size more by weight than length - large specimens are broad across the head and shoulders and are heavily built.
Conservation Status

Vulnerable, Listed under the Victorian Flora & Fauna Guarantee Act
Threatened, Species of National Significance, Listed under the Commonwealth Environmental Protection & Biodiversity Conservation (EPBC) Act


Distribution
Distribution map of Murray cod

Widespread throughout the Murray-Darling system originally being found in vitually all waterways of that system, including some surprisingly small streams. The main exceptions were tiny tributaries and the alpine headwaters of some southern rivers within the basin. Murray cod were extremely abundant in the past and the species was in fact the most common of the larger native fish in the Murray-Darling system at the time of European settlement.

Today Murray cod are massively reduced in numbers. Wild stocks are now estimated to be less than ten percent of the population present at the time of European settlement. Unfortunately, Cod have become locally extinct in many small tributaries in which they once abounded, particularly in upland reaches of the southern and central Murray Darling Basin, and the fish is rare in the majority of the rest of its original range.

Murray cod have been stocked into many water reservoirs throughout the Eastern states and are a popular fish for farm dams in warmer areas. Some re-stocking of river populations has occurred but the most important tool in restoring cod populations to something like their former glory is the appropriate management of the river systems. This is a nettle yet to be fully grasped by government due to the inherent high costs involved.
Habitat

Murray cod are remarkable by any ecologist's standards in their adaptability and the diversity of habitats they occupy. Murray cod habitat varies greatly, from quite small clear, rocky, upland streams with riffle and pool structure on the upper western slopes of the Great Dividing Range to large, meandering, slow-flowing, often silty rivers in the alluvial lowland reaches of the Murray-Darling Basin.

It should be noted that Murray cod are not just inhabitants of the lowland reaches of the Murray Darling Basin (MDB), as is commonly believed. Murray cod had, and in some cases still do have, a significant presence in the upland reaches of the MDB. At the time of European settlement Murray cod appear to have had an altitudinal limit of around 700 metres in the southern half of the MDB, and around 1000 metres in the northern half.

Murray cod prefer deep holes with cover in the form of large rocks, fallen trees, stumps, clay banks and overhanging vegetation.

Very territorial.
Diet

(Top Predator) Murray cod have a varied diet of other fish, spiny freshwater crayfish, Yabbies, shrimp, freshwater mussels, frogs, water fowl, small mammals, tortoises and other reptiles. Virtually anything within its realm that moves and is small enough to fit in its cavernous mouth is considered fair game!


Reproduction

Reaches sexual maturity at 4 to 5 years of age and 2 to 3 kg in weight. Murray cod have relatively low fecundity (fertility) compared to many other freshwater fish. Egg counts range from &lt10,000 eggs for a barely mature female to approximately 90,000 for females around the 22 kg mark.

Breeding of Murray cod is a complicated subject, not yet fully understood. Based on preliminary research from the 1960s, it is popularly believed Murray cod need spring floods to breed, will not spawn in reservoirs and dams, spawn on the actual floodplain in times of flood, and do not migrate. Research has demonstrated that none of these beliefs are correct.

Evidence suggests that Murray cod spawn in spring every year, whether there is a flood or not. Rising water temperatures and increasing photo-period (or length of daylight) are the cues for breeding. If a spring flood coincides with this general ripening period, however, it often will trigger breeding. 20&degC is usually quoted as the temperature threshold for breeding, but this appears to be flexible, and there are strong indications of Murray cod breeding at lower temperatures in Victoria.

Murray cod form pairs prior to breeding. A spawning site is selected, usually a sunken red gum log in lowland rivers, or a submerged rock in upland streams, although Murray cod have been recorded excavating and laying eggs in depressions in clay banks as well. The female is believed to clean the breeding site with her tail before laying her large adhesive eggs as a large mat on the spawning surface. The male then squirts his milt over the eggs fertilising them. The male will then guard and fan the eggs until they hatch in 6-10 days, continuong to guard the larvae for a week or so after hatching by which time they have absorbed the yolk-sac and have become free-swimming. Growth of hatched Murray cod in rivers in southern NSW has been estimated at 230, 340, 460, 560, and 640 mm after years one to five respectively.

Spring floods are critical for high survival of Murray cod larvae, as they create an explosion of zooplankton (tiny aquatic insects) that are the critical food for newly-hatched Murray cod and other native fish. Survival rates of larvae spawned in reservoirs, dams and non-flooded rivers are extremely low due to a lack of zooplankton, In these situations most Murray cod larvae will starve to death.

Will breed in reservoirs, as well as in earthen dams in captivity if provided with suitable spawning sites. 200 litre (44 gal) drums with the ends removed are suitable structures in a farm dam. Fisheries and commercial breeders often use more sophisticated devices to facilitate the removal of eggs, but the general idea is to simulate a large submerged hollow log. In commercial and fisheries department situations, spawning structures are examined for eggs and when present they are removed to a hatchery for incubation. If left in the structure, as would usually be the case in a farm dam, a much lower survival rate is to be expected, although this is not really a problem in that case.

For a long time fish researchers believed Murray cod were sedentary and non-migratory (albeit ignoring the anecdotal evidence of anglers, many of whome had observed strong upstream spawning migrations of Murray cod). The question was settled with a Murray cod radio tracking project in the early 1990s. Large Murray cod were fitted with transmitting radio tags and tracked by foot, boat and aeroplane, revealing that Murray cod make strong upstream spawning migrations in late winter and spring. Migratory tendencies and distances travelled varied considerably between individual Cod, but many fish travelled 40 or 50 kilometres upstream and some travelled up to 120 kilometres upstream. Floods were important in stimulating these migrations - fish tended not to migrate if there were no floods Interestingly, most Murray cod returned downstream to the exact same snag after spawning migrations. This remarkable homing behaviour is almost unknown in freshwater fish and emphasises the importance of snags to Murray cod.

Radio-tracking and other research suggests that larger native fish and particularly Murray cod do not spawn on the actual floodplain in times of flood, but spawn on the flooded margin of the main river channel. It appears that eggs are spawned on and hatch in the heavy timber at the edge of the river channel, and, after hatching the larvae lurk at the edge of the river channel, nailing prey as the food-rich floodplain waters spill over the edge of the river channel.

Murray cod are extremely long-lived. The oldest specimen yet recorded is 48 years of age, but they reaches far greater ages, most likely as much as 100 years. Extreme longevity is a survival strategy for many native fish and particularly Murray cod. These fish survive many years to capitalise on exceptional conditions for spawning and recruitment, when those conditions occur.


History

Murray cod, although arising from a marine ancestor like most freshwater fish, are nonetheless an ancient species. Fossils of fish anatomically identical to modern Murray cod have been unearthed in NSW from strata dating to 26 millions years ago. However, it is possible the species is as old as the Murray-Darling Basin itself about 50 to 60 million years.

Prior to European colonisation aboriginal people were able to exploit the species as a major food source using relatively simple technologies aided by the fish's great abundance. They were impressed by the Murray cod, for in addition to being a major food source, it was the largest, most abundant and most beautiful of the native fish species. These people had and still do have enormous respect and reverence for the Murray cod. The importance of Murray cod to aboriginal people of the Murray-Darling basin is reflected by the fact that many groups living along the Murray River made the Murray cod a central animal in their mythology, including their creation stories. Many Murray River groups believed that the wide reaches and bends of the Murray River were created by a giant Murray cod, swimming down the formerly narrow trickle to the sea, while being pursued by a dream-time hero.

In modern Australia, the Murray cod is nation's largest and best-known freshwater fish. The stuff of legends, the Murray cod is represented in practically every pub in South Eastern Australia by photos and mounted examples. Stories abound of titanic struggles with the almost supernatural fish. Ply an old codger with a few beers and you are likely to hear how when he was a boy one of the local water holes was inhabited by some gigantic Cod. The story usually goes along the lines that some farmer lost a large bait to the fish and kept coming back with heavier and heavier tackle until eventually he turned up with a whole kangaroo as bait on a meat hook connected to the steel cable of the winch on his tractor. The fish in the story then fights the farmer and his tractor to a standstill, usually resulting in the demise of said tractor. You are then invited to inspect the wreck of the machine under an ancient red gum tree near the pub and shown the stretch of water which was straightened by the fish in the struggle!

On a more sersious note, Murray cod were originally extremely common and supported a substantial commercial fishery in the nineteenth century and in the early decades of the twentieth. Records from this fishery indicate that Murray cod were numerically the dominant native fish in the Murray-Darling system until the 1950s.


Decline

The decline in Murray cod numbers is due to multiple factors. Contrary to popular belief, overfishing has played a massive role in the decline of Murray cod. Murray cod were grotesquely overfished by commercial fishermen in the latter half of the nineteenth century. For instance, in year 1883, more than 147 tons of Murray cod were sent to market from just one port (Moama). It is staggering to think that that real figure, incorporating unreported catches, was probably at least double that. It boggles the imagination to think what the total catch for all ports may have been.

During this time, recreational fishermen also massively overfished the species. Old photographs abound of recreational anglers stringing up literally dozens of massive Murray cod at a time. The fishery must have seemed inexhaustable. Sadly today we know that it was not.

By the very early 1900s, alarm was expressed at the decline of Murray cod and a Royal Commission was held on the decline of Murray cod. Unfortunately, no decisive action resulted.

Finally, once overfishing had severly damaged Murray cod stocks, an even more potent agent of decline was to take over - river regulation. The many dams and weirs, and the regulation of river flows that they allow, mean that rivers do not follow natural flow patterns anymore. In particular, the spring floods that create the zooplankton-rich conditions, vital for strong survival and recruitment of Murray cod larvae, have been curtailed or halted completely. With no spring floods Murray cod are simply unable to recruit numbers effectively (the overwhelming majority of cod larvae produced every year starve to death) and Murray cod stocks have consequently crashed.

Dams and weirs have other impacts as well:

* they halt important breeding migrations;
* they allow excessive water extraction for irrigation; and,
* they release extremely cold water, as the result of low level water outlets, which dramatically reduce river temperatures to the point where native fish cannot breed, native fish larvae cannot survive, and indeed sometimes native fish cannot exist at all. This problem, often termed "thermal pollution" or "cold water pollution", is a serious threat, and can affect rivers for anything up to 200 kilometres downstream of a large dam.

Another major cause of decline is river-desnagging. Hundreds of thousands of snags have been removed from Murray-Darling system. Almost unbelievably this still occurs, though thankfully the practice is now frowned upon and is even illegal in some areas. The damage this de-snagging has done to native fish, especially Murray cod, is incalculable. Snags are critical habitat for Murray cod at all sizes, vital spawning sites, and in the silty alluvial lowland rivers of the Murray-Darling system, one of the few hard substrates available and thus critical sites for algae, bacteria, fungi and aquatic invertabrates. In other words, snags are critical sites for food production and ecosystem function in our lowland rivers. Some researchers have described large red gum snags, hundreds or even thousands of years old (redgum are virtually impervious to rot), as the coral reefs of our lowland rivers.

Yet another significant problem, particular for upland rivers or smaller lowland rivers holding Murray cod, has been siltation of the stream bed through clearing of native riparian (river-bank) vegetation and the effects of introduced large, hard-hoofed animals such as cattle which trample the river banks.

Cattle (whichever variety) very quickly obliterate riparian vegetation and crush river banks, destroying the structure of the river. This leads to rapid, massive siltation of deep holes which are habitat for native fish and a complete loss of stream bed diverity which is required by the entire aquatic ecosystem. This is the death knell for Murray cod in these rivers, as well as for the ecosystems concerned. This long established farming practice is unfortunately still widespread and is often unrecognised for the problem it represents. The broad shallow sandy-bottommed streams produced as a result are very picturesque to the casual observer. Consequently it is very difficult to explain to land owners the importance of keeping stock away from streams. Some leadership is needed at all levels of government to get cattle away from all river banks, and to have all rivers replanted with their native riparian vegetation.

Speaking of vegetation, willows are also a problem - to Murray cod, to native fish in general and to rivers and their ecosystems. Compared to indigenous trees willows are incredibly greedy with water, and can suck a small river dry. They cause deoxygenation with mass autumn leaf dumps, wipe out many species of native aquatic invertebrates (fish food) reliant on better water quality and continous leaf fall from native vegetation for food and have other negative effects. Willows are not an asset, and the sooner they are replaced with vegetation native to streams the better.

Murray cod have been stocked into many water reservoirs throughout the Eastern states and are a popular fish for farm dams in warmer areas. However, there are serious inbreeding problems with some hatchery breeding of Murray cod. Inbreeding can produce unhealthy fish and loss of the genetic variation required to be a healthy adaptable predator in the wild, both as individuals and at the population level. Due to logistics, the fish hatcheries produce will always have lower genetic diversity compared to wild bred fish. Thus, hatchery breeding and stocking of Murray cod is not the magic answer and will not ensure their long term survival. (Stocking of hatchery bred Murray cod in rivers can actually cause damage, as remnant wild Cod populations with their diverse gene pool are swamped by hordes of hatchery Cod with a narrow gene pool - as little as two parents in a worst case scenario.)

The only way to ensure the long term survival of Murray cod is to have healthy breeding populations in the wild which requires healthy rivers and more natural flow regimes. This in turn will require some drastic changes to the way we currently manage river catchmentss in Australia, an issue which politicians seem reluctant to tackle head-on or to provide effective leadership for.


Other Cod species

Trout cod Maccullochella macquariensis are a second species of Cod found in the Murray-Darling system, now critically endangered. They appear to be a Cod that has speciated into a specialist inhabitant of the cooler upper reaches of rivers, but their range does overlap with that of Murray cod.

Trout cod have been severely adversely effected by the introduction of trout into upland habitats throughout their range.
Distribution map of Mary River cod

Murray cod have also managed to cross the Great Dividing Range into coastal river systems at least once during their long existence on the Australian continent, via ancient river capture events. Due to isolation from cod of the Murray-Darling Basin, these coastal Cod have diverged into separate species. At the time of European settlement, 4 coastal rivers in northern NSW and southern QLD (the Clarence, Richmond, Brisbane and Mary Rivers) held naturally occurring populations of Cod.

The Richmond River and Brisbane River Cod unfortunately became extinct in the 1950s. Decades of habitat destruction and gross over fishing by European settlers were followed by whole-of-catchment scale bushfires and massive ash fish kills in the late 1930s, causing a terminal decline. The Cod of the Clarence River and Mary River survive, although both are endangered.
Distribution map of Eastern freshwater cod

Clarence River cod are named Eastern freshwater cod Maccullochella ikei being a separate species in the same genus as Murray cod. Based on mitochondrial DNA divergence rates, it is estimated that Cod crossed into the Clarence system somewhere between 0.8 and 1.7 million years ago, with the older date considered more likely.

Mary river cod Maccullochella peelii mariensis are currently formally classified as a sub-species of Murray cod. However, recent genetic analysis now indicates they are actually a sub-species of Eastern freshwater cod. Should this prove to be the case, then their scientific name will change to Maccullochella ikei mariensis.
Distribution map of Mary River cod

This finding has interesting implications. It suggests, for example, that Murray cod only crossed the Great Dividing Range once (into the Clarence River system) and then leap-frogged north into the next 3 river systems via further river capture events albeit dodging the Tweed River. It suggests that all four coastal Cod populations are/were actually sub-species of Eastern freshwater cod Maccullochella ikei.

Another possibility is that the fish did not miss the Tweed river system on their way up the coast. Rather, there may have been cod in that system in the pre-European past. Subsequently then, the fish became extinct before European settlement perhaps as a result of whole-of-catchment scale bushfires and subsequent massive ash fish kills similar to an event which almost claimed Eastern freshwater cod about 2000 years ago, as revealed by genetic analysis. Unfortunately, the likelyhood of ever finding fossil evidence for this is vanishingly small. However, we do have the evidence of the event (as mentioned earlier) which did in fact claim the Richmond and Brisbane River fish in the early twentieth century after their very dramatic decline caused by the early settlers, which suggests that the "cod in the Tweed" scenario is possible.

The Richmond River has now been restocked with Cod from the Clarence River system, while the Brisbane River has now been restocked with Cod from the Mary River system. Grave inbreeding problems have recently surfaced with the breeding and stocking of Cod of the Clarence River system. It is questionable as to whether the genetic guidelines required to be followed in this program have indeed been followed. Breeding and stocking of Cod for the Clarence River has now been suspended for the time being.

The coastal Cod are remarkable fish. Their coastal river habitats can be radically different to Murray cod habitats. For example, former Cod holding tributaries of the Richmond and Brisbane River are rainforest streams with cobble bottoms, tannin-stained water and rainforest trees and ferns - the Cod of these streams were veritable rainforest Cod. It is hard to imagine a more different environment to that which exists through most of the Murray-Darling. As a matter of interest, restocked coastal Cod are doing well in these streams now. It is testament to the resilience and adaptability of the Cod that it has been able to survive in such radically different habitats.
Angling

Generally regarded as Australia's premier freshwater angling species, the powerful Murray cod can be a difficult customer to deal with. Most cod specialists use relatively heavy tackle. Line breaking strains in the 40 to 50 lb or even higher are common amongst those aiming for the larger fish. The new super braided lines have proven useful, especially when trolling in heavy cover, which is where you find the fish.

Cod respond well to large baits and lures. Many cod specialists fish only large trolled or cast deep diving lures with a wide action at dead slow speed. Surface lures work well at night and large flies have been tried with success. Bardi grubs, Yabbies, shrimps and scrub worms all catch cod. Cod have even been caught on such diverse baits as rabbits and hard boiled eggs! If using fly, you need heavy gear, as cod can pull like a steam train. Even small cod will take very large baits and lures, and give you a run for your money to boot.

Fish close to snags and other structure - if you're not getting snagged up, you're not fishing in the right place!

Size and bag limits and closed seasons apply in all States where Murray cod occur, so check your local regulations.

Murray cod are excellent eating in the smaller legal sizes, up to around 6-8 Kg. Can be filleted or steaked and are great on the barbeque. Larger fish can be very oily and are best still swimming in the river <grin>. If fishing for the table NFA recommends that you fish in impoundments that have been stocked by fisheries, rather than in river systems supporting wild populations.

In fac, NFA strongly encourages you to practice catch and release when fishing for Murray cod. This especially applies with large fish which are important breeding stock for the species and which are less palatable in any case.

Recent research has shown that all cod species caught and released during the period prior to the spawning season (ie during winter) re-absorb their eggs and thus do not participate in the breeding season. For this reason NFA very strongly recommends that cod not be targetted during winter, especially so for naturally recruited populations. Please avoid fishing for cod in rivers and most importantly Lake Mulwala, during this time. It is also most important to avoid fishing for Eastern Cod (which are totally protected anyway) or in Eastern Cod habitats at this time. If you feel you really must fish for cod during winter, please target only Murray cod in impoundments supported by stocking and without natural recruitment (this does not include Lake Mulwala).
In the aquarium

Smaller examples make excellent and very impressive aquarium specimens. Juvenile hatchery bred Murray cod are readily available through the aquarium trade. Murray cod should be kept on their own as they are very territorial and aggressive to other fish, including their own species. Best fed on a mixed diet of live yabbies, shrimp (if available) and fish, although cod are easily trained to accept dead food. For anglers, a diet of skinned fillets of carp are an easy to obtain and cheap food. A standard 3 foot aquarium is satisfactory for a small cod, but make sure the space you use will accept a much larger tank. Popular tank sizes (in feet) for cod are 4x2x2 up to 6x2x2 or even 6x3x2, a six foot tank will last a fish for many years. Cod are very strong fish and the tank should be made from heavy glass and have a heavy cover as the fish can accidentally jump out if it makes a strike at an insect on the surface, or even a bubble!
On the web

Australian Desert Fishes Pages - Murray Cod

South Australian Department of Primary Industries: Murray Cod
 
Last edited:

Nuriel

AC Members
Sep 6, 2004
519
0
16
Seattle, Wa. USA
www.43things.com
Nuriel said:
In the aquarium

Smaller examples make excellent and very impressive aquarium specimens. Juvenile hatchery bred Murray cod are readily available through the aquarium trade. Murray cod should be kept on their own as they are very territorial and aggressive to other fish, including their own species. Best fed on a mixed diet of live yabbies, shrimp (if available) and fish, although cod are easily trained to accept dead food. For anglers, a diet of skinned fillets of carp are an easy to obtain and cheap food. A standard 3 foot aquarium is satisfactory for a small cod, but make sure the space you use will accept a much larger tank. Popular tank sizes (in feet) for cod are 4x2x2 up to 6x2x2 or even 6x3x2, a six foot tank will last a fish for many years. Cod are very strong fish and the tank should be made from heavy glass and have a heavy cover as the fish can accidentally jump out if it makes a strike at an insect on the surface, or even a bubble!
note how it says smaller examples???? as in, juvinile? dang, these fish can live for 60+ years?!?! i guess one would raise it for a couple years then release? I have no idea about australias laws on that type of thing. i would think that since the fish is protected it would be illegal to keep at home, but evidently not.
 
Last edited:

ashdavid

In Search Of Better Water Quality
Mar 27, 2005
1,268
1
0
Japan
Sorry i should clarify a little on my requests.What i did mean to say that i would like to see a native Australian fish in the profiles. I know it would be hard to house for most people but the Arapaima gigas(Pirarucu) or the aligator gar(among many others) is on the speices profile which would take just as big a home or even biger to thrive IMHO, and isn't the specise profile just for that purpose to inform people about a particular species.(no offence intended).

Nuriel said:
note how it says smaller examples???? as in, juvinile? dang, these fish can live for 60+ years?!?! i guess one would raise it for a couple years then release? I have no idea about australias laws on that type of thing. i would think that since the fish is protected it would be illegal to keep at home, but evidently not.
It is allowed to be caught by fishermen therefore they do promote releasing back into the wild and because they have breeding programs(which you can buy fingerlings for about $5) to restock rivers and supply for human consumption, it can be easily obtained in the aquarium trade. The Trout cod on the other hand cannot be taken under any circumstance as it is fully protected. It looks very similar the the murry cod but only smaller.
They do live a very long time and you would have to be commited. But they are beautiful fish IMHO.
 

ashdavid

In Search Of Better Water Quality
Mar 27, 2005
1,268
1
0
Japan
Who does the species profiles anyway?
 
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