Australian grayling
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| Australian grayling | ||||||||||||||
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| Prototroctes maraena Günther, 1864 |
The Australian grayling (Prototroctes maraena) is a primarily freshwater fish found in coastal rivers in Tasmania and south-eastern Australia. In past decades it has also been known as the “cucumber mullet” or “cucumber herring,” for its cucumber-like odor.
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[edit] Description and Diet
The Australian grayling is a stream-lined fish with a streamlined, vaguely trout-like shape. Colouration is usually silver on the flanks and dusky olive on the back, overlain with a gold sheen.
Australian grayling commonly grow to around 17 cm (though some have reached 33 cm) and can live up to 6 years. The fish has an omnivorous diet, feeding upon algae, shrimp, and small insects.
[edit] Reproduction
Australian grayling spawn in the freshwater reaches of coastal rivers. Spawning is thought to occur in late autumn or early winter. McDowall (1996) reports that egg counts range from 25,000 to 67,000 in females 170–200 mm long, and that the small (~1 mm) demersal eggs probably settle among gravel and cobble in the river bed before hatching. Hatched larvae are washed out to sea. Australian grayling juveniles return to the freshwater reaches of rivers after roughly 6 months at sea and spend the rest of their lives in river habitats.
[edit] Angling
Before the introduction of exotic trout species to Australia, an introduction that has caused severe problems for the conservation of Australian native fish, Australian grayling, along with spotted galaxias, were keenly fished for by early Australian anglers using fly-fishing gear. The species was appreciated for its willingness to take wet and dry flies, its excellent fighting ability on very light tackle, and its relatively large size. A handful of fly-fishers in Australia are now re-discovering the pleasure of fly-fishing for this magnificent native fish with ultra-light fly-fishing tackle.
[edit] Historical Declines and Current Threats
Australian grayling suffered massive initial declines in 1869–70 by very large, unexplained fish kills (Saville-Kent, 1888). Descriptions of grayling killed in this event of being covered in "cottony growths" suggests a fungal pathogen, possibly marking the arrival of exotic Saprolegnia fungus into Australian freshwater habitats thanks to the reckless importation of exotic salmonid species.
Saville-Kent then went on to consider the apparent epidemic some 17–18 years previously which had caused the demise of the Australian grayling Prototroctes maraena. The grayling were said to "have been seen floating down the rivers in thousands, covered more or less extensively with a cottony fungoid growth. So virulent and exhaustive was this epidemic that many, more especially of the southern rivers, were more or less completely denuded of their stock of this species and have so remained up to the present date". Saville-Kent posed the questions of how, when and where the epidemic originated and whether at the time there were any abnormal conditions associated with the rivers carrying the infected fish. He went on to say: "The approximate date of the appearance of this epidemic would appear to be about the year 1869 or 1870, periods it may be remarked of great activity in association with the distribution of the fry of the newly acclimatised Salmonidae in the rivers of this colony. Is it possible ...that the fungus, ‘’Saprolegnia’’, was hitherto unknown to Tasmania and was introduced with the ova of these Salmonidae, or more probably in the moss wherein they were packed? Under such conditions the germs or spores, like the microbes of measles or smallpox, arriving on a virgin and congenial soil, might be expected to spread with devastating virulence among the aboriginal inhabitants." (Cadwallader, 1996)
Today Australian grayling are threatened by dams and weirs blocking migration and fragmenting river habitats, irresponsible forestry and farming practices that degrade river environments through siltation and other effects, and competition and predation by exotic trout species. Scientific tudies have shown native fish species similar in habitat and lifestyle such as spotted galaxias are severely depressed in number in rivers inhabited by exotic trout species (Ault & White, 1994), and are forced into sub-optimal feeding locations, feeding times and diets by aggressive competition from exotic trout species (McDowall, 2006). A chronic lack of exotic-trout-free habitat reserved for galaxias species and other native fish species in south-eastern Australia generally is a major concern.
Australian grayling are a protected species under Australia’s Environment Protection and Biodiversity Conservation Act.
[edit] References
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This article or section includes a list of references or external links, but its sources remain unclear because it lacks in-text citations. You can improve this article by introducing more precise citations. |
- Ault, T.R. and White, R.W.G. (1994) Effects of habitat structure and the presence of brown trout on the population density of Galaxias truttaceus in Tasmania, Australia. Transactions of the American Fisheries Society 123: 939–949.
- Cadwallader, P.L. (1996) Overview of the Impacts of Introduced Salmonids on Australian Native Fauna. Australia Nature Conservation Agency, Canberra.
- McDowall, R.M. (ed.) (1996) Freshwater Fishes of South-Eastern Australia. Reed Books, Sydney.
- McDowall, R.M. (2006) Crying wolf, crying foul, or crying shame: alien salmonids and a biodiversity crisis in the southern cool-temperate galaxioid fishes? Rev Fish Biol Fisheries 16: 233–422.
- Saville-Kent, W, 1888. On the acclimatisation of the salmon (Salmo salar) [and exotic trout species] in Tasmanian waters, and upon the reported disease at the breeding establishment on the River Plenty. Papers and Proceedings of the Royal Society of Tasmania 1887: 54–66.
- Wager (1996). Prototroctes maraena. 2006 IUCN Red List of Threatened Species. IUCN 2006. Retrieved on 10 May 2006. Listed as Vulnerable (VU A1c v2.3)
- Prototroctes maraena (TSN 623684). Integrated Taxonomic Information System. Retrieved on 24 January 2006.
- "Prototroctes maraena". FishBase. Ed. Ranier Froese and Daniel Pauly. 10 2005 version. N.p.: FishBase, 2005.
