Maccullochella peelii peelii
Other Common Names
Cod, codfish, goodoo, greenfish, Murray perch (incorrectly, in fishmongers)
Will reach at least 60 cm and 3 to 4 Kg in the small streams.
Murray Cod in larger waterways usually reach 90 to 100 cm and 15 to 20
Kg, if not taken by anglers. Occasionally recorded from 120 to 130 cm and
35 to 45 Kg.
The largest Murray cod ever officially recorded was 183 cm, 113 Kg (6
ft, 250 lbs), although there have been unsubstantiated claims for larger
Unfortunately, excessive recreational fishing pressure has lead to a serious
lack of large, mature brood fish in wild populations with an almost total
absence of year classes above 50 cm (the minimum legal angling size) throughout
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.
Vulnerable, Listed under the Victorian Flora & Fauna
Threatened, Species of National Significance, Listed under the Commonwealth
Environmental Protection & Biodiversity Conservation (EPBC) Act
Widespread throughout the Murray-Darling system originally being found
in virtually 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
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.
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
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.
(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
Reproduction and Biology
Murray cod are extremely long-lived. Specimens regularly
reach ages of 30-35 years. The oldest specimen yet recorded is 48 years
of age, but they
almost certainly reach far greater ages, most likely as much as 100 years.
Extreme longevity is a survival strategy for many native fish and particularly
Murray cod. This enables them to outlast prolonged periods of drought,
so as to capitalise on exceptional conditions for spawning and recruitment
when they do occur. SE Australia's current (as at May 2007) decade-long
drought is a case in point of the sort of prolonged dry period which has
figured in Australia's climate for millenia — on average a drought
of this magnitude occurs about once every century or so — and is
just the sort of event for which Murray cod have had to develop a survival
Murray cod reach sexual maturity at 4 to 6 years
of age (most fish 5 years) and 2 to 3 kg in weight. The species has relatively
low fecundity (fertility)
compared to many other freshwater fish. Egg counts range from <10,000
eggs for a barely mature female to approximately 90,000 for females around
the 22 kg mark. It is likely that large female Murray cod that are in the
15-25 kg range and "in their prime" are perhaps the most important
breeders because they produce the most eggs and for other reasons; research
is now showing 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 (e.g. Trippel, 1995;
Marteinsdottir & Steinarsson, 1998; Marteinsdottir & Begg, 2002).
Both 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. Such large females may also have
valuable, successful genes to pass on.
Breeding of Murray cod is a complicated subject, not yet fully understood,
although great strides have been made in that understanding in recent years.
Based on preliminary research from the 1960s, it is popularly believed
that Murray cod need spring floods to breed, will not spawn in reservoirs
and dams, spawn on the actual floodplain in times of flood, do not migrate
and, to make matters worse, the lowland Murray-Darling rivers in low flow
conditions lack the necessary food for Murray cod larvae. Research has
demonstrated that none of these beliefs are correct.
In reality: Murray cod will breed with or without spring-floods, including
in low flow conditions in lightly regulated rivers; they will spawn in
reservoirs and farm dams (although survival of larvae is very poor, for
reasons not known); cod do not spawn on the floodplain; and, Murray cod
actually undertake quite significant migrations. Further, lowland rivers
in low flow conditions abound in benthic (river-bed-based) zooplankton
that Murray cod and other native fish larvae can and do feed on.
It should be noted that the now out dated spring-flood only theory, with
its emphasis on floodplain inundation, only ever applied to lowland river
habitats, and not the many upland river habitats in which Murray cod were
and sometimes still are found, since upland rivers generally do not have
floodplains, a fact that seems to have been overlooked!
The picture has now changed when it comes to the breeding biology of Murray
cod. Previously Murray cod were considered by many to be odd fish with
odd larvae that do not survive unless they hatch into extremely food-rich,
spring-flood conditions. Today this fish is recognised as an adaptable
and flexible one with large, well-nourished, strongly swimming and flexible
larvae. These larvae are evolved to survive and recruit under a variety
of natural river flow conditions and habitats, including during times of
low flow as well as in upland habitats. In lowland habitats, while Murray
cod have recruited most strongly in the past under spring-flood conditions,
and those conditions may well be the most ideal for Murray cod recruitment,
it is clear that successful recruitment in low flow conditions is possible
and does actually occur.
A number of caveats apply:
* Recruitment of Murray cod in low flow conditions requires rivers that
are in reasonable environmental health, are not heavily regulated, and
offer reasonable habitat for all life-stages;
* Heavy river regulation does appear to create recruitment failure in Murray
cod for reasons that are not yet clear;
* The creation of impoundments also appears to create recruitment failure in
Murray cod, despite the species commonly spawning in impoundments, for reasons
that are also not yet clear; and,
* Spring-floods are still essential for river ecosystems, including maintaining
fish habitat and allowing the migration of adult and juvenile Murray cod and
for recolonisation of areas of low population. Indeed, the virtual elimination
of spring floods from the Murray-Darling system due to river regulation is
of great concern.
However, given that we now know Murray cod can recruit to some extent
in low flow conditions, it is still an excellent question as to is why
Murray cod do not recruit more successfully in low conditions in more lightly
regulated rivers in the Murray-Darling Basin. Other reasons for this poor
recruitment in these rivers must be found. Likely culprits include severe
and continuing over fishing of spawning adults, desnagging and other habitat
loss and massive competition between Murray cod larvae and (literally)
billions of exotic carp larvae (carp being an illegal and enormously damaging
introduction to Australia and the Murray-Darling River system).
On a more general note, research over the last several decades, has revealed
the general spawning biology of Murray cod to be as follows:
Female Murray cod carry out the majority of egg development over winter
(June, July, August), prior to their spring spawning. Anglers are advised
that research indicates capture and release of Murray cod brood fish in
winter causes resorption of the eggs and spawning failure (Lake, 1967;
Rowland, 1988, 2005). As a result, NFA discourages targeting this species
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°C 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.
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 logs and occasionally clay banks in
lowland rivers, at a depth of 2 to 3 m, 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 6-10 days (depending on water temperature),
and to guard the hatched larvae for a further week or so until they leave
the nest site (dispersal). Larvae leave the nest site by drifting in river
currents at night, and continue this behaviour for around 4-7 days. During
this dispersal process, larvae simultaneously absorb the rest of their
yolk sac and begin to feed on pelagic ("surface layer") zooplankton,
small, early life-stage macroinvertebrates and epibenthic/epiphytic (bottom
dwelling/edge clinging) microinvertebrates.
Murray cod 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 whom 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.
These radio-tracking studies and other research demonstrates that Murray
cod do not spawn on the actual floodplain during spring-flood conditions,
as was previously conjectured, but rather, they spawn on the flooded margin
of the main river channel. It appears that under these conditions, eggs
are spawned on and subsequently hatch in the heavy timber at the edge of
the channel and, after hatching, the larvae lurk at the edge of the channel,
intercepting zooplankton and other prey as the food-rich floodplain waters
spill over the edge of the channel. The overall picture is of a fish that
spends the vast majority of its life cycle within the main river channel.
Indeed contrary to earlier beliefs, Murray cod could be considered to be
a main channel specialist at all life stages.
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 super natural
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 serious 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.
The decline in Murray cod numbers is due to multiple factors. Contrary
to popular belief, over fishing has played a massive role in the decline
of Murray cod. Murray cod were grotesquely over fished 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 inexhaustible.
Sadly today we know that it was not. Yet, excessive angler kill continues
to cause profound problems for these long-lived fish.
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 over fishing had severely 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,
these dams and weirs curtail or halt completely the spring floods in lowland
rivers that create the zooplankton-rich conditions which are one of the
conditions under which the strongest recruitment occurs. With no spring
floods, Murray cod are unable to recruit in large numbers in many lowland
rivers and opportunities for migration and colonisation are also lost.
All the while river ecosystems lose productivity boosts and events that
maintain habitat. Meanwhile, heavy river regulation and/or habitat loss,
competition with exotic carp larvae and other factors preclude or diminish
recruitment in low flow conditions in many lowland rivers.
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 desnagging 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
invertebrates. 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-hooved animals such as cattle which trample the
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 diversity 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-bottomed 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.
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 continuous 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 catchments in Australia, an issue
which politicians seem reluctant to tackle head-on or to provide effective
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
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 likelihood 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.
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
In fact, 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
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
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!
Murray cod will do well in unheated aquarium indoors,
but generally it is best to use a heater to put a floor under the temperature.
this way the heater should be set to around 18°C at which temperature
the fish will remain active and feeding all year round. Some enthusiasts
will set the temperature up to around 24°C while the fish are young
to encourage fast growth until the fish reaches a size of around 150-200
mm when it may conveniently be fed on live feeder fish. The heater is then
gradually turned down to 18°C - if done in summer, this can be achieved
without risk of chilling the fish since ambient temperatures are likely
to be above 20°C anyway in most places.
Very small Murray cod, such as those newly purchased from an aquarium
shop, sometimes appear to be very timid and will hide much of the time.
Most fish will grow out of this, however you can assist the progress by
providing plenty of cover for the fish, depending on fish size such things
as small sections of PVC tube, broken terracotta flower pots and so on
will help the fish become more confident. In particular many young Murray
cod do not like to have a light coloured substrate and these fish will
feel more secure if the substrate is darker, or if running in a bare tank,
with a sheet of dark plastic under the tank.
Like for most Australian native fish, salt is a very useful agent for
managing the health of captive Murray cod. A salinity of 0.5 to 1 gram
per litre is a good general purpose tonic for maintenance and in times
of illness or stress the salinity can be bumped up to 6-8 g/l. The salt
acts to reduce stress and in particular osmotic stress in sick or injured
fish, as well as helping control parasites such as white spot or Lernaea,
which may be accidentally introduced with feeder fish. As an aid to reducing
the likelihood of this sort of introduced infection, it is best if all
live food is quarantined for at least a week, but if this is not possible,
the food can be placed in a salt bath (a salt solution of around 10 g/l)
for an hour or so prior to feeding it to the Murray cod. When using salt,
it must not contain any additives like Iodine, copper salts (often used
in swimming pool salt in tropical areas) or free flow agent (used in some
cooking salt). Ideally use sea salt but if it is unavailable a good, inexpensive
source is to buy swimming pool salt, just make a call to the manufacturer
and ask if the particular brand available to you is suitable for aquaculture.
Water quality is important and pH should be maintained at neutral or slightly
alkaline ideally at around 7.0-7.5, although a range of 7.0 to 8.0 is acceptable.:nbsp;
Care should be taken to prevent the water becoming acidic and the use of
granular Calcium Carbonate (do not use powder) or shell grit is recommended
to act as a pH buffer. If running at an elevated temperature or if feeding
heavily it is important to monitor ammonia levels and any trace of ammonia
shown by a test kit should be treated as an emergency and a significant
water change (at least 30%) should be undertaken immediately.
Murray cod make very rewarding aquarium fish and often become very attached
to their owners. Many owners hand feed their fish and if kept in a location
where there is a lot of activity they can become very interactive. A Murray
cod of around 50 to 60 cm is certain to provoke comment from your visitors!