Eastern Freshwater Cod
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{{Taxobox | color = pink | name = Eastern Freshwater Cod | regnum = Animalia | phylum = Chordata | classis = Actinopterygii | ordo = Perciformes | familia = Percichthyidae | genus = Maccullochella | species = M. ikei | binomial = Maccullochella ikei | binomial_authority = Rowland, 1986 }} Eastern Freshwater Cod (Maccullochella ikei), also known as Eastern Cod, are a large and striking predatory freshwater fish of the Maccullochella genus and the Percichthyidae family. They are closely related to the Murray Cod of the Murray-Darling river system.
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Range
Eastern Freshwater Cod are native to the Clarence and Richmond Rivers and their tributaries, which are East Coast drainages in northern New South Wales, Australia. They are similar in appearance to Murray Cod, M. peelii peelii.
Appearance and size
Eastern Freshwater Cod are generally a yellow green to golden colour, overlain with a dense pattern of black to very dark green mottling. Eastern Freshwater Cod have been recorded to 41 kg. Image:Small Eastern freshwater cod.jpg
Habitat, Diet and Spawning
Eastern Freshwater Cod are found in clear, flowing rivers and streams with rocky beds and deep holes within the Clarence River system. The size of the rivers and streams they inhabit range from very small to very large. Image:Eastern freshwater cod habitat.jpg
Eastern Freshwater Cod are territorial and aggressive. They are known to prey upon other fishes, frogs, crustaceans and snakes. A long-lived, slow-growing species, they are gravely threatened by overfishing, habitat degradation and catastrophic natural events such as bushfires. Original populations in the Richmond River system are extinct, but have been re-established with fingerlings produced from broodfish from the Clarence River system.
Eastern Freshwater Cod are now protected by law.
Eastern Freshwater Cod are sexually mature at 4 or 5 years old, and at sizes as small as 700 grams, the latter being markedly different to Murray Cod. This far smaller size at sexual maturity may be an adaptation to small, food-impoverished waterways. Eastern Freshwater Cod spawn in early spring when water temperatures reach 16° C, using rock structures as sites for the adhesive eggs. Most other aspects of their spawning, including the guarding of eggs and newly hatched larvae by the male fish, are similar to Murray Cod. It is important for anglers to avoid any accidental captures of Eastern Freshwater Cod in winter when they are developing their roe, or in early spring when spawning is occurring, as research indicates this results in resorbed roe or abandoned nests and a failed spawning effort. Anglers are not allowed to deliberately target Eastern Freshwater Cod.
Origins
Eastern Freshwater Cod are a separate species of Cod that originated from the Murray Cod (Maccullochella peelii peelii) that are present in tributaries of the Murray-Darling Basin on the western side of the Great Dividing Range. Murray Cod entered the headwaters of the Clarence River system through a natural river capture event somewhere between 0.8 and 1.7 million years ago, as estimated by DNA divergence rates. Subsequent isolation from Murray Cod populations, the founder effect, genetic drift and natural selection all led Eastern Freshwater Cod to diverge from and become a separate species to Murray Cod. (See allopatric speciation.)
It is not clear whether Murray Cod only crossed the Great Dividing Range once or several times to found the four coastal cod populations present in four coastal river systems at the time of European settlement. Eastern Freshwater Cod may be the parent species of all coastal cod populations including Mary River Cod (Maccullochella peelii mariensis), another coastal cod species occurring in the Mary River in central Queensland, although this is not currently reflected in the taxonomy. See Mary River Cod for details.
Conservation
At the time of the first European settlement of the Australia in the 18th century, naturally occurring cod populations were present in four East Coast river systems: the Clarence and Richmond Rivers in northern New South Wales and the Brisbane and Mary Rivers in southern/central Queensland. The original cod populations of the Richmond and Brisbane River systems are unfortunately extinct due to the same factors that have endangered extant cod populations in the Clarence River (Eastern Freshwater Cod) and the Mary River (Mary River Cod): gross overfishing including with nets and explosives, gross habitat destruction and siltation, and whole-of-catchment scale bushfires and subsequent ash fish kills in the 1930s.
Eastern Freshwater Cod were recognised as a potentially separate and endangered species of Cod in 1984, and were declared a protected species in that year. Subsequent research confirmed they are indeed a separate and endangered species of Cod; they remain a protected species.
A restocking programme was undertaken by the government of New South Wales in from 1984 to 1989. The government-run stocking programme was ill-advisedly closed after 1989 and contracted to a private operation, which produced and stocked fingerlings until the late 1990s. The Eastern Freshwater Cod stocking programme was then suspended after genetic research indicated inbred fingerlings with extremely poor genetic diversity, that could threaten the genetics of remnant wild populations, were being produced and stocked.
No Eastern Freshwater Cod are currently being bred or stocked.
The NSW fisheries department has allowed the private operation that produced Eastern Freshwater Cod fingerlings to retain broodfish and produce captive-reared Eastern Freshwater Cod for the table fish market - a decision that most people involved in conservation of Australian native freshwater fish consider indefencable and vehemently object to.
There are grave concerns over the future of all Eastern Freshwater cod stocks in the Clarence River system after the NSW Fisheries department allowed a foolhardy stocking of Australian Bass fingerlings from a completely different bio-region to proceed. The fingerlings were contaminated with and introduced the Banded Grunter (Amniataba percoides) to the lower reaches of the river. The Banded Grunter is an extremely aggressive small native fish species. It is feared Banded Grunter may yet invade the main freshwater reaches of the Clarence River system with devestating impacts on Eastern Freshwater Cod.
References
- Template:ITIS
- Template:FishBase species
- Rowland, S.J. 1993. Maccullochella ikei, an endangered species of freshwater cod (Pisces: Percichthyidae) from the Clarence River System, NSW, and M.peelii mariensis, a new subspecies from the Mary River System, QLD. Records of the Australian Musuem 45: 121-145.
- Rowland, S.J. 1996. Threatened fishes of the world: Maccullochella ikei
- Rowland, 1985 (Percichthyidae). Environmental Biology of Fishes 46: 350