Australian grayling
Encyclopedia
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.
Australian grayling commonly live for 2–3 years and reach around 20 cm in length, although rare individuals have been recorded up to 5 years in age and 33 cm in length. The fish has an omnivorous diet, feeding upon algae
, shrimp
, and small insect
s.
, 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.
s (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.
Today Australian grayling are threatened by a number of things. Dams and weir
s block migration
and also block floods and reduce base flows, both of which are important for habitat maintenance and for spawning and movement of grayling larvae and juveniles to and from the sea. Irresponsible forestry and farming practices degrade and fragment river environments through siltation and other effects. Exotic trout
species threaten grayling through predation and competition. 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 listed as a vulnerable species under Australia’s Environment Protection and Biodiversity Conservation Act 1999.
Tasmania
Tasmania is an Australian island and state. It is south of the continent, separated by Bass Strait. The state includes the island of Tasmania—the 26th largest island in the world—and the surrounding islands. The state has a population of 507,626 , of whom almost half reside in the greater Hobart...
and south-eastern 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...
. In past decades it has also been known as the “cucumber mullet” or “cucumber herring,” for its cucumber-like odor.
Description and Diet
The Australian grayling is a streamlined 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 live for 2–3 years and reach around 20 cm in length, although rare individuals have been recorded up to 5 years in age and 33 cm in length. The fish has an omnivorous diet, feeding upon algae
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
, shrimp
Shrimp
Shrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...
, and small 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.
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.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 galaxiasSpotted galaxias
-Introduction:Spotted galaxias are a largish, primarily-freshwater galaxias species found in southern Australia. Spotted galaxias are perhaps the most beautiful of the Australian galaxias species...
, 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.
Historical Declines and Current Threats
Australian grayling suffered massive initial declines in 1869–70 by very large, unexplained fish killFish kill
The term fish kill, known also as fish die-off and as fish mortality, is a localized die-off of fish populations which may also be associated with more generalised mortality of aquatic life...
s (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
Saprolegnia
Saprolegnia is a genus of freshwater mould often called a "cotton mould" because of the characteristic white or grey fibrous patches it forms. Current taxonomy puts Saprolegnia as a genus of the heterokonts in the order Saprolegniales.-Habits:...
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."
Today Australian grayling are threatened by a number of things. Dams and weir
Weir
A weir is a small overflow dam used to alter the flow characteristics of a river or stream. In most cases weirs take the form of a barrier across the river that causes water to pool behind the structure , but allows water to flow over the top...
s block migration
Fish migration
Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousands of kilometres...
and also block floods and reduce base flows, both of which are important for habitat maintenance and for spawning and movement of grayling larvae and juveniles to and from the sea. Irresponsible forestry and farming practices degrade and fragment river environments through siltation and other effects. Exotic trout
Trout
Trout is the name for a number of species of freshwater and saltwater fish belonging to the Salmoninae subfamily of the family Salmonidae. Salmon belong to the same family as trout. Most salmon species spend almost all their lives in salt water...
species threaten grayling through predation and competition. 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 listed as a vulnerable species under Australia’s Environment Protection and Biodiversity Conservation Act 1999.
Further reading
- 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. (1976) Fishes of the Family Protroctidae (Salmoniformes). Australian Journal of Freshwater and Marine Research 27: 641–659.
- 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. Listed as Vulnerable (VU A1c v2.3)