Jump to content

Trout cod

From Wikipedia, the free encyclopedia

This is an old revision of this page, as edited by 202.174.40.174 (talk) at 01:59, 7 June 2006 (→Description). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

Trout Cod
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Actinopterygii
Order:
Perciformes
Family:
Percichthyidae
Genus:
Maccullochella
Species:
M. macquariensis
Binomial name
Maccullochella macquariensis
Cuvier, 1829

The Trout Cod (Maccullochella macquariensis) is a large and striking predatory freshwater fish of the Maccullochella genus and the Percichthyidae family and was originally found in the south-east corner of the Murray-Darling river system in Australia. It is closely related to Murray Cod. Trout cod were originally known in the nineteenth century as Murray cod-perch. In the early twentieth century they were known as blue-nose cod or just blue-nose in Victoria and as trout cod in New South Wales, the latter common name being adopted when the species status of the fish was finally confirmed by genetic studies in the 1970s. 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

The Trout Cod is a very horny fish, it has sex atleast 55 times a day and it's dick may grow up to 80 cm and 16 kg, but there are unconfirmed anecdotal accounts of larger specimens. It is very similar in appearance to the Murray Cod, M. peelii peelii. It has a light, greyish "dirty-looking" ventral surface with generally blue-grey to dark brown colouration across the lateral and dorsal surfaces overlaid with a speckled pattern of dark grey or bluish grey to black spots. These speckles reduce in intensity or are missing over the head and the base colouration intensifies in this area. Most specimens have a horizontal line through the eye which can be indistinct, broken into irregular sections or be very marked and almost jet black.

The dorsal fin has a spined section partially separated by a notch from the anterior soft-rayed section. Anterior dorsal, caudal and anal fins are dark grey to black with white edges identical to Murray Cod. Ventral fins are translucent and the pelvic fins are dark grey, carried well forward with the leading, white coloured ray extended to form a bifurcated filament. Trout cod have a more pointed snout compared to Murray Cod and have an overhanging upper jaw. Overall conformation and colouration of the fins and body form are otherwise similar to 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 Nineteenth century trout cod were recognised by the scientific community as separate species, due to differing habitat preferences, morphological differences (especially 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 idea that they were really just anomalous Murray cod gained currency.

Habitat

Although there is substantial overlap in range, Trout Cod are essentially a specialised upland form of Murray Cod. Therefore, the Trout Cod's main habitats were the larger upland rivers and creeks, which they usually co-inhabited with Macquarie perch and one or both of the Blackfish species. Recently collated oral histories are confirming a primarily upland distribution for Trout cod. 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 being (lowland - upland):

Golden Perch (Macquaria ambigua) - Macquarie Perch (Macquaria australasica);

Estuary Perch (Macquaria colonorum) - Australian Bass (Macquaria novemaculeata);

River Blackfish (Gadopsis marmoratus) - Two-Spined Blackfish (Gadopsis bispinosis); and

Flathead Galaxias (Galaxias rostratus) - Mountain Galaxias species complex (Galaxias spp.).

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 mussells, crustaceans, aquatic insects, 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.

Trout cod tend to stick to areas of deep water near banks, around snags, rocks or other large structure. Generally speaking Trout cod have small home ranges and they are 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.


Spawning

Trout Cod reach sexual maturity at 3-5 years (which corresponds to about 35cm in males and 43cm 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. Spawing 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 captivity in earthen dams; 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. It is worth noting that introduced Trout species are absent from this stretch of river.

Historical records leave us in no doubt Trout Cod (and Macquarie perch) occurred 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 signficant stretches of unregulated, high quality habitat. It is almost certain that the main reason for the Trout Cod's extinction in its upland river habitats, and its current endangered status, is the complete domination of every one of its upland river habitats by introduced Trout species, which are aggressive, predatory fish. There is strong historical, biological, anecdotal and circumstantial evidence to support this.

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. Many are still continually stocked with introduced Trout species despite the presence of endangered upland native fish species. 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 these constant liberations of introduced Trout species have been stark. 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, 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.

The New South Wales Fisheries Department has acknowledged predation on juvenile Trout Cod by introduced Trout species in recent literature. Several publications in the 1940s through to the 1960s by the director of the Victorian Fisheries and Game Department (A.D.Butcher) documents predation on juvenile Trout Cod, Macquarie perch and other upland native fish species by introduced Trout species, and major dietary overlaps.

Scientific studies to document and quantify the impacts of introduced Trout on Trout Cod and Macquarie perch are 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.

It is likely that Trout Cod and Macquarie perch will remain endangered until they are provided with sizeable, Trout-free upland river habitats. 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 fishermen of south-eastern Australia are missing out on a unique part of their heritage; a beautiful upland native fish that was vastly superior in sporting and fighting qualities to introduced Trout species and that their forefathers raved about.

References

  • "Maccullochella macquariensis". Integrated Taxonomic Information System. 19 March. {{cite web}}: Check date values in: |date= and |year= / |date= mismatch (help)
  • Froese, Rainer; Pauly, Daniel (eds.). "Maccullochella macquariensis". FishBase. October 2005 version.
  • Butcher, A.D. 1945. The food of indigenous and non-indigenous freshwater fish in Victoria, with special reference to [introduced] Trout. Fisheries Pamphlet 2. Fisheries and Wildlife Department, Victoria.
  • Butcher, A.D. 1967. A changing aquatic fauna in a changing environment. IUCN Publications, New Series 9: 197-218.
  • Cadwallader, P.L. (ed.) 1977. J.O. Langtry's 1949-50 Murray River Investigations. Fisheries and Wildlife Paper. Ministry for Conservation, Victoria.
  • Cadwallader, P.L. 1979. Distribution of native and introduced fish in the Seven Creeks river system, Victoria. Australian Journal of Ecology 4: 361-385.
  • Cadwallader, P.L. & Gooley, G. 1984. Past and present distributions and translocations of Murray Cod and Trout Cod in Victoria. Proceedings of the Royal Society of Victoria 96,1: 33-43.
  • Merrick, J.R. & Schmida, G.E. 1984. Australian Freshwater Fishes; Biology and Management. Griffin Press, Australia.
  • Rhodes, J.O. 1999. Heads and Tales: Recollections of a Fisheries and Wildlife Officer. The Australian Deer Research Foundation Ltd, Melbourne.
  • Trueman, W. and Luker, C. 1992. Fishing Yesteryear. Freshwater Fishing Australia Magazine 17: 34-38.


Retrieved from "https://en.wikipedia.org/enwiki/w/index.php?title=Trout_cod&oldid=57284033"