Trout Cod
Encyclopedia
The trout cod or bluenose cod, Maccullochella macquariensis, is a large predatory freshwater fish of the Maccullochella
genus and the Percichthyidae family which was originally found in the south-east corner of the Murray-Darling river system in Australia
. It is closely related to the Murray cod
.
In the 19th and early 20th centuries, when trout cod were widely recognised as a separate species by commercial fishermen, recreational fishermen, riverside residents and fisheries scientists, they were generally known as bluenose cod or simply bluenose, particularly in Victoria
. In some parts of New South Wales
however they were also known as trout cod, and this common name was adopted when the species status of the fish was finally confirmed by genetic studies in the early 1970s. This choice of official common name was perhaps unfortunate; it has been suggested that bluenose cod is a more appropriate name as the name trout cod causes confusion amongst the Australian public. (Trout cod are an Australian native freshwater fish; they are not a hybrid between Murray cod and introduced trout species.)
Trout cod are a listed species on a number of different registers including Endangered under the New South Wales Fisheries Management Act 1994, the Australian Commonwealth’s Environment Protection and Biodiversity Conservation Act 1999, the Australian Capital Territory's Nature Conservation Act 1980 and by the World Conservation Union (IUCN). They are also listed as Threatened under the Victorian Flora and Fauna Guarantee Act 1998.
Trout cod are broadly similar to the Murray cod, however there are some distinct differences in morphology and colouration.
Trout cod are a small to medium groper-like fish with a deep, elongated body that is round in cross section. In contrast to Murray cod, trout cod have a pointed head with the top jaw overhanging the bottom jaw, and the slope of the head is straight. The eyes are slightly larger and more prominent than in Murray cod. The head tends to be free of speckling however a distinct dark stripe through the eye is usually present.
Trout cod are cream to light grey on their ventral (“belly”) surfaces. Their back and flanks are most commonly bluish-grey in colour, overlain with irregular black speckling, but this can be highly variable depending on the habitat specimens come from, and can range from almost white to light grey-green, light brown, dark brown or almost black. The black speckling on the back and flanks is consistent however.
The spiny dorsal fin is moderate 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 light grey to dark grey or black with distinct white edges. The large, rounded pectoral fins are usually similar in colour to flanks. The pelvic fins are large and 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 cream or light grey.
Smaller trout cod tend to be more slender than equivalent sized Murray cod; curiously, very large trout cod appear to develop deeper shoulders than equivalent sized Murray cod.
While trout cod were only conclusively described as a separate species to Murray cod in 1972, commercial and recreational fishermen and early fishery biologists were in no doubt that there were two separate species of cod in the Murray-Darling system from the 1850s onwards, and noted the trout cod's different appearance and spawning biology and preference for cooler, faster flowing water and upland habitats. During the 19th and early 20th centuries trout cod were recognised by the scientific community as separate species, due to differing habitat preferences, morphological differences (especially the much smaller size at sexual maturity) and differing spawning times. It was really only post World War II
— by which time trout cod had become very rare or even extinct in much of their original range — that the erroneous idea that they were really just anomalous Murray cod gained any currency.
and one or both of the blackfish
species. Historical research is confirming a primarily upland distribution for trout cod; recent governmental literature lacking such historical research and suggesting trout cod are primarily a lowland fish species must be considered inaccurate.
Division into specialist upland and primarily lowland species is a relatively common phenomena in native fish genera of the Murray-Darling and East Coast systems with other notable pairs are shown in the following table:
Trout cod are often found close to cover and in faster currents and in cooler waters than Murray cod. Their diet is essentially the same as Murray cod with adjustment made for size, eating mainly other fishes, freshwater mussels
, crustacean
s, aquatic insect
s, small mammals and water fowl. However, recent anecdotal evidence suggests terrestrial insects made up a significant proportion of the trout cod's diet in upland rivers and streams.
In the surviving Murray River population trout cod tend to stick to areas of deep water near banks, around snags, rocks or other large structure. However, historical accounts of trout cod in upland river habitats stated that trout cod were often found in shallow riffles and runs. Generally speaking, radio-tracked trout cod in the surviving Murray River population have small home ranges and may be a species which does not move away from their original base, except during the breeding season when they follow a common trend in Murray-Darling fish of migrating upstream prior to spawning. It seems likely that trout cod follow a similar pattern to Murray cod and return post spawning to their original location.
In more lowland river habitats, river regulation and habitat degradation through activities like de-snagging, and overfishing, are probably the primary causes of decline. Heavy predation by introduced redfin perch
, which were present in great numbers in the lowland reaches of the southern MDB for several decades, also played a large role in the decline of native fish in those reaches including trout cod. The possibility that trout cod populations in upland habitats were the ultimate source of trout cod populations in lowland habitats (i.e. source and sink populations) over long time frames (i.e. decades) cannot be discounted however. Historical accounts such as those from J.O.Langtry indicate lowland trout cod populations were secondary populations in secondary habitats, clearly in the minority to more abundant primarily lowland native fish species such as Murray cod, golden perch and silver perch. Therefore it is doubtful whether strong trout cod populations can ever be established in lowland habitats, and therefore the issue of upland habitats, and the return of some upland habitats in trout-free form, needs to be addressed in trout cod conservation.
Historical evidence indicates trout cod (and Macquarie perch) were abundant in most of the larger upland rivers and streams in the south-east corner of the Murray-Darling river system, and that these upland river habitats were their primary habitats. The extinction of trout cod populations in every one of its upland river habitats is an unresolved issue. Contrary to popular belief, many of these upland rivers still contain significant stretches of unregulated, high quality habitat. While dams, thermal pollution, siltation and other forms of habitat modification and degradation are responsible for the trout cod's extinction in many upland river habitats, it is almost certain that the reason for the trout cod's extinction in higher quality upland river habitats, that have not experienced serious modification and degradation, is the heavy domination of these habitats by introduced trout species, which are aggressive, predatory fish.
Every single larger upland river and stream in south-eastern Australia is dominated by introduced trout species (rainbow trout and brown trout), with many having been continually stocked with introduced trout species for more than a century, and not a single larger upland river or stream in south-eastern Australia has been reserved in a trout-free state for larger upland native fish species. The effects of this course of action by fishery departments has been stark, and catastrophic events such as drought or bushfire, after which introduced trout species were restocked but upland native fish were not restocked, have shifted the balance further. The net result is that a number of upland native fish species including trout cod (and Macquarie perch) have completely died out or nearly so in their upland river habitats in the wild, apparently unable to cope with massive predation on their larvae/juveniles by introduced trout species and unable to cope with massive competition from introduced trout species for food and habitat at all life stages.
Scientific studies to document and quantify the impacts of introduced trout on trout cod (and Macquarie perch) in upland river habitats, and develop a more scientific approach to trout cod conservation and re-establishment efforts, including in upland river habitats, are desperately needed. Given the strong cultural cringe towards introduced trout in the wider community and the management bias towards introduced trout amongst fishery agencies these studies may be some way off.
Two small populations of trout cod that have shown indications of breeding have been created by hatchery stockings in the lowland reaches of Murrumbidgee River
at Gundagai and Narranderra, although it is far from clear whether these populations will be self-sustaining in the long term. Many other stockings of trout cod have failed, which is not surprisingly considering the small number of trout cod fingerlings stocked, and the that fact that trout cod were frequently stocked into upland river habitats where introduced trout species wer heavily entrenched, and in at least one case, were carried in conjunction with far larger stockings of introduced trout. A semi-natural population exists in a stretch of the very small upland Seven Creeks, which was established by translocations of trout cod (and Macquarie perch) above a set of falls in the 1920s. The Seven Creeks population is not a wholly artificial population, or a wholly unrepresentative habitat, as often claimed, as some of the trout cod translocated came — literally — from the base of the falls.
In the meantime the fishers of south-eastern Australia are missing out on a unique part of their heritage; a beautiful upland native fish that is vastly superior in sporting and fighting qualities compared to introduced trout species, and was revered by early fishers.
Maccullochella
Maccullochella is a genus of large Australian predatory freshwater fish within the Percichthyidae family. The Maccullochella genus was named after an early Australian fish researcher with the surname McCulloch....
genus and the Percichthyidae family which was originally found in the south-east corner of the Murray-Darling river system in Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
. It is closely related to the Murray cod
Murray Cod
The Murray cod is a large Australian predatory freshwater fish of the Maccullochella genus and the Percichthyidae family. Although the species is a called cod in the vernacular, it is not related to the northern hemisphere marine cod species...
.
In the 19th and early 20th centuries, when trout cod were widely recognised as a separate species by commercial fishermen, recreational fishermen, riverside residents and fisheries scientists, they were generally known as bluenose cod or simply bluenose, particularly in Victoria
Victoria (Australia)
Victoria is the second most populous state in Australia. Geographically the smallest mainland state, Victoria is bordered by New South Wales, South Australia, and Tasmania on Boundary Islet to the north, west and south respectively....
. In some parts of New South Wales
New South Wales
New South Wales is a state of :Australia, located in the east of the country. It is bordered by Queensland, Victoria and South Australia to the north, south and west respectively. To the east, the state is bordered by the Tasman Sea, which forms part of the Pacific Ocean. New South Wales...
however they were also known as trout cod, and this common name was adopted when the species status of the fish was finally confirmed by genetic studies in the early 1970s. This choice of official common name was perhaps unfortunate; it has been suggested that bluenose cod is a more appropriate name as the name trout cod causes confusion amongst the Australian public. (Trout cod are an Australian native freshwater fish; they are not a hybrid between Murray cod and introduced trout species.)
Trout cod are a listed species on a number of different registers including Endangered under the New South Wales Fisheries Management Act 1994, the Australian Commonwealth’s Environment Protection and Biodiversity Conservation Act 1999, the Australian Capital Territory's Nature Conservation Act 1980 and by the World Conservation Union (IUCN). They are also listed as Threatened under the Victorian Flora and Fauna Guarantee Act 1998.
Description
Trout cod have been reliably recorded to at least 80 cm and 16 kg, but there are some credible anecdotal accounts of larger specimens.Trout cod are broadly similar to the Murray cod, however there are some distinct differences in morphology and colouration.
Trout cod are a small to medium groper-like fish with a deep, elongated body that is round in cross section. In contrast to Murray cod, trout cod have a pointed head with the top jaw overhanging the bottom jaw, and the slope of the head is straight. The eyes are slightly larger and more prominent than in Murray cod. The head tends to be free of speckling however a distinct dark stripe through the eye is usually present.
Trout cod are cream to light grey on their ventral (“belly”) surfaces. Their back and flanks are most commonly bluish-grey in colour, overlain with irregular black speckling, but this can be highly variable depending on the habitat specimens come from, and can range from almost white to light grey-green, light brown, dark brown or almost black. The black speckling on the back and flanks is consistent however.
The spiny dorsal fin is moderate 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 light grey to dark grey or black with distinct white edges. The large, rounded pectoral fins are usually similar in colour to flanks. The pelvic fins are large and 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 cream or light grey.
Smaller trout cod tend to be more slender than equivalent sized Murray cod; curiously, very large trout cod appear to develop deeper shoulders than equivalent sized Murray cod.
While trout cod were only conclusively described as a separate species to Murray cod in 1972, commercial and recreational fishermen and early fishery biologists were in no doubt that there were two separate species of cod in the Murray-Darling system from the 1850s onwards, and noted the trout cod's different appearance and spawning biology and preference for cooler, faster flowing water and upland habitats. During the 19th and early 20th centuries trout cod were recognised by the scientific community as separate species, due to differing habitat preferences, morphological differences (especially the much smaller size at sexual maturity) and differing spawning times. It was really only post World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
— by which time trout cod had become very rare or even extinct in much of their original range — that the erroneous idea that they were really just anomalous Murray cod gained any currency.
Habitat
Although there is/was a very substantial overlap in range, trout cod are essentially a more specialised upland sister species to Murray cod. Therefore, the trout cod's main habitats were the larger upland rivers and creeks, which they usually co-inhabited with Macquarie perchMacquarie perch
The Macquarie perch is an Australian native freshwater fish of the Murray-Darling river system. It is a member of the Percichthyidae family and is closely related to the golden perch ....
and one or both of the blackfish
Two-spined blackfish
The two-spined blackfish, Gadopsis bispinosus, is an Australian native freshwater fish. It is a speciated, more specialised upland variant of the river blackfish, Gadopsis marmoratus....
species. Historical research is confirming a primarily upland distribution for trout cod; recent governmental literature lacking such historical research and suggesting trout cod are primarily a lowland fish species must be considered inaccurate.
Division into specialist upland and primarily lowland species is a relatively common phenomena in native fish genera of the Murray-Darling and East Coast systems with other notable pairs are shown in the following table:
| Upland | Lowland |
|---|---|
| Macquarie perch Macquarie perch The Macquarie perch is an Australian native freshwater fish of the Murray-Darling river system. It is a member of the Percichthyidae family and is closely related to the golden perch .... , Macquaria australasica |
Golden perch Golden perch The golden perch, Macquaria ambigua, is an Australian native freshwater fish, primarily of the Murray-Darling river system. It is not a true perch of the genus Perca.... , Macquaria ambigua |
| Australian bass Australian bass Australian bass are a small to medium sized, primarily freshwater native fish found in coastal rivers and streams along the east coast of Australia. They are a member of the Percichthyidae family and, currently, the Macquaria genus. Australian bass are an iconic, highly predatory native fish... , Macquaria novemaculeata |
Estuary perch Estuary perch The estuary perch, Macquaria colonorum, is an Australian species of the Percichthyidae family.It is very similar to and very closely related to its sister species the Australian bass, Macquaria novemaculeata... , Macquaria colonorum |
| Two-spined blackfish Two-spined blackfish The two-spined blackfish, Gadopsis bispinosus, is an Australian native freshwater fish. It is a speciated, more specialised upland variant of the river blackfish, Gadopsis marmoratus.... , Gadopsis bispinosis |
River blackfish River Blackfish The river blackfish, is an Australian native freshwater fish of the Murray-Darling river system, found from southern Queensland through to central Victoria. It is also found in some eastern and southern flowing coastal rivers... , Gadopsis marmoratus |
| Mountain galaxias species complex Mountain galaxias The mountain galaxias species complex is a group of freshwater Galaxiid fish found all over southeast Australia. They form a cryptic species complex.-Classification:These fish were originally designated as a single species, Galaxias olidus, despite:... , Galaxias spp. |
Flathead galaxias Flathead galaxias (Australia) The flathead galaxias, Galaxias rostratus, is a freshwater fish found in lowland rivers and streams and associated billabongs, backwaters, etc of the southern Murray-Darling river system in Australia.... , Galaxias rostratus |
Trout cod are often found close to cover and in faster currents and in cooler waters than Murray cod. Their diet is essentially the same as Murray cod with adjustment made for size, eating mainly other fishes, freshwater mussels
Unionidae
Unionidae is a family of freshwater mussels, the largest in the order Unionoida, the bivalve mollusks sometimes known as river mussels, naiads, or simply as unionids.The range of distribution for this family is world-wide...
, crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s, aquatic insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s, small mammals and water fowl. However, recent anecdotal evidence suggests terrestrial insects made up a significant proportion of the trout cod's diet in upland rivers and streams.
In the surviving Murray River population trout cod tend to stick to areas of deep water near banks, around snags, rocks or other large structure. However, historical accounts of trout cod in upland river habitats stated that trout cod were often found in shallow riffles and runs. Generally speaking, radio-tracked trout cod in the surviving Murray River population have small home ranges and may be a species which does not move away from their original base, except during the breeding season when they follow a common trend in Murray-Darling fish of migrating upstream prior to spawning. It seems likely that trout cod follow a similar pattern to Murray cod and return post spawning to their original location.
Diet
Trout cod are carnivores and feed on other fish, crustaceans (such as crayfish, yabbies and freshwater shrimp) as well as aquatic and terrestrial insects.Reproduction
Trout cod reach sexual maturity at 3 to 5 years (which corresponds to about 35 cm in males and 43 cm in females). Trout cod reach sexual maturity at a smaller size than Murray cod, which is an adaptation to the rocky, low nutrient and often quite small upland habitats trout cod were found in. Spawning of trout cod has never been observed in the wild and is not well understood. It is believed to be essentially the same as Murray cod but occurs about three weeks earlier and at significantly lower temperatures in waters shared by the two species. Trout cod are believed to spawn at temperatures as low as 15 degrees in upland rivers, using rocks as a spawning substrate; these are also clear adaptations to cool, rocky upland river habitats. Significantly, and unlike Murray cod, trout cod will not breed in earthen dam brood ponds; another indication that trout cod are a more specialised upland species than Murray cod. Artificial breeding programs being conducted for the species recovery use hormone injections to induce ovulation in naturally ripe fish in spring.Conservation
Trout cod were once quite abundant, but are now gravely threatened by overfishing, environmental factors and introduced trout species and are listed as endangered. The species is now totally protected. Only one wild, naturally occurring trout cod population remains in the Murray River in a region where the river is basically an extended transition zone from upland river habitat to lowland river habitat.In more lowland river habitats, river regulation and habitat degradation through activities like de-snagging, and overfishing, are probably the primary causes of decline. Heavy predation by introduced redfin perch
European perch
The European perch, Perca fluviatilis, is a predatory species of perch found in Europe and Asia. In some areas it is known as the redfin perch or English perch, and it is often known simply as perch. The species is a popular quarry for anglers and has been widely introduced beyond its native area,...
, which were present in great numbers in the lowland reaches of the southern MDB for several decades, also played a large role in the decline of native fish in those reaches including trout cod. The possibility that trout cod populations in upland habitats were the ultimate source of trout cod populations in lowland habitats (i.e. source and sink populations) over long time frames (i.e. decades) cannot be discounted however. Historical accounts such as those from J.O.Langtry indicate lowland trout cod populations were secondary populations in secondary habitats, clearly in the minority to more abundant primarily lowland native fish species such as Murray cod, golden perch and silver perch. Therefore it is doubtful whether strong trout cod populations can ever be established in lowland habitats, and therefore the issue of upland habitats, and the return of some upland habitats in trout-free form, needs to be addressed in trout cod conservation.
Historical evidence indicates trout cod (and Macquarie perch) were abundant in most of the larger upland rivers and streams in the south-east corner of the Murray-Darling river system, and that these upland river habitats were their primary habitats. The extinction of trout cod populations in every one of its upland river habitats is an unresolved issue. Contrary to popular belief, many of these upland rivers still contain significant stretches of unregulated, high quality habitat. While dams, thermal pollution, siltation and other forms of habitat modification and degradation are responsible for the trout cod's extinction in many upland river habitats, it is almost certain that the reason for the trout cod's extinction in higher quality upland river habitats, that have not experienced serious modification and degradation, is the heavy domination of these habitats by introduced trout species, which are aggressive, predatory fish.
Every single larger upland river and stream in south-eastern Australia is dominated by introduced trout species (rainbow trout and brown trout), with many having been continually stocked with introduced trout species for more than a century, and not a single larger upland river or stream in south-eastern Australia has been reserved in a trout-free state for larger upland native fish species. The effects of this course of action by fishery departments has been stark, and catastrophic events such as drought or bushfire, after which introduced trout species were restocked but upland native fish were not restocked, have shifted the balance further. The net result is that a number of upland native fish species including trout cod (and Macquarie perch) have completely died out or nearly so in their upland river habitats in the wild, apparently unable to cope with massive predation on their larvae/juveniles by introduced trout species and unable to cope with massive competition from introduced trout species for food and habitat at all life stages.
I regret not knowing the name of a man I met at Tom Groggin Station, a Victorian property on the Indi River near Mt Kosciusko, who told me that he worked at Tom Groggin before he enlisted in the army and went to the first World War. He had fished the Indi before he left and it carried a great number of blue nose [trout cod], white eye [Macquarie perch] and greasies [blackfish]. While he was at war, he even dreamt about fishing the Indi. When he came home he returned to his old job at Tom Groggin and announced that before he did any work, he wanted to go fishing. Very quickly he caught a fish about a foot (30cm) in length, the like of which he had never seen before. So intrigued was he by this strange spotted but nicely shaped fish that he immediately took it to the homestead thinking it was something quite unique. At the homestead, he was told it was a brown trout. From that time both the white eye [Macquarie perch] and the blue nose [trout cod] numbers went into decline, while the numbers of brown and rainbow trout increased. To my mind, this man did do something remarkable, he had set a very positive timeframe of a change over of fish species in the Indi River.
Heads and Tales: Recollections of a Fisheries and Wildlife Officer.
Scientific studies to document and quantify the impacts of introduced trout on trout cod (and Macquarie perch) in upland river habitats, and develop a more scientific approach to trout cod conservation and re-establishment efforts, including in upland river habitats, are desperately needed. Given the strong cultural cringe towards introduced trout in the wider community and the management bias towards introduced trout amongst fishery agencies these studies may be some way off.
Two small populations of trout cod that have shown indications of breeding have been created by hatchery stockings in the lowland reaches of Murrumbidgee River
Murrumbidgee River
The Murrumbidgee River is a major river in the state of New South Wales, Australia, and the Australian Capital Territory . A major tributary of the Murray River, the Murrumbidgee flows in a west-northwesterly direction from the foot of Peppercorn Hill in the Fiery Range of the Snowy Mountains,...
at Gundagai and Narranderra, although it is far from clear whether these populations will be self-sustaining in the long term. Many other stockings of trout cod have failed, which is not surprisingly considering the small number of trout cod fingerlings stocked, and the that fact that trout cod were frequently stocked into upland river habitats where introduced trout species wer heavily entrenched, and in at least one case, were carried in conjunction with far larger stockings of introduced trout. A semi-natural population exists in a stretch of the very small upland Seven Creeks, which was established by translocations of trout cod (and Macquarie perch) above a set of falls in the 1920s. The Seven Creeks population is not a wholly artificial population, or a wholly unrepresentative habitat, as often claimed, as some of the trout cod translocated came — literally — from the base of the falls.
The future?
With emerging historical evidence emphasising upland river habitats as the original primary habitat for trout cod (and Macquarie perch), and casting serious doubt over attempts to re-establish self-sustaining populations in lowland habitats, this species will likely remain endangered until it is provided with a few sizeable, trout-free upland river habitats. This process could be undertaken with no serious impacts on the economically and recreationally important introduced trout fisheries in Australia, and indeed could be of great benefit to fishermen and fisheries. However, this appears to be a nettle that no fishery or conservation agency is prepared to grasp, again due to strong cultural cringe towards introduced trout in the wider community and the management bias towards introduced trout amongst fishery agencies.In the meantime the fishers of south-eastern Australia are missing out on a unique part of their heritage; a beautiful upland native fish that is vastly superior in sporting and fighting qualities compared to introduced trout species, and was revered by early fishers.
External links
- Native Fish Australia Trout cod page
- Australian Government Department of the Environment and Heritage - Recovery Plan for the Trout Cod Maccullochella Macquariensis 1998 - 2005
- Australian Museum - Australian Museum Fish Site
- New South Wales Department of Primary Industries - cod recovery plan
- New South Wales Department of Primary Industries - cod fishnote