The Australian grayling (''Prototroctes maraena'') is a primarily

freshwater fish Freshwater fish are fish species that spend some or all of their lives in bodies of fresh water such as rivers, lakes, ponds and inland wetlands, where the salinity is less than 1.05%. These environments differ from marine habitats in many wa ...

found in coastal rivers in south-eastern mainland Australia and

Tasmania Tasmania (; palawa kani: ''Lutruwita'') is an island States and territories of Australia, state of Australia. It is located to the south of the Mainland Australia, Australian mainland, and is separated from it by the Bass Strait. The sta ...

. In past decades it has also been known as the cucumber mullet or cucumber herring, for its

cucumber The cucumber (''Cucumis sativus'') is a widely-cultivated creeping vine plant in the family Cucurbitaceae that bears cylindrical to spherical fruits, which are used as culinary vegetables. 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 in length, although rare individuals have been recorded up to at least 5 years in age and in length. The fish has an omnivorous diet, feeding upon

algae Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthesis, photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular ...

shrimp A shrimp (: shrimp (American English, US) or shrimps (British English, UK)) is a crustacean with an elongated body and a primarily Aquatic locomotion, swimming mode of locomotion – typically Decapods belonging to the Caridea or Dendrobranchi ...

, and small

insect Insects (from Latin ') are Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (Insect morphology#Head, head, ...

s. They have specially adapted teeth and a long gut to help with the digestion of algae.

Reproduction

Australian grayling spawn following movements to the lower 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 A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect developmental biology, development such as insects, some arachnids, amphibians, or cnidarians typical ...

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.Kaminskas S (2024). Migratory Flows and Stochastic Blows: A study of Australian grayling (''Prototroctes maraena'') and other native fish species of the Deua River, New South Wales, Australia. Published by the author, Canberra, Australia. http://dx.doi.org/10.13140/RG.2.2.24039.05283

Angling

Before the introduction of alien ("introduced") fish species including the eastern mosquitofish and trout to Australian waterways the Australian grayling and spotted galaxias were keenly fished by recreational 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. However, due to declining numbers the fish is now protected under the

Environment Protection and Biodiversity Conservation Act 1999 The ''Environment Protection and Biodiversity Conservation Act 1999'' (Cth) is an Act of the Parliament of Australia that provides a framework for protection of the Australian environment, including its biodiversity and its natural and cult ...

. Heavy penalties apply for taking any of the fish.

Historical declines and current threats

Australian grayling suffered massive initial declines in 1868–1870 through very large, unexplained

fish kill The term fish kill, known also as fish die-off, refers to a localized mass mortality event, mass die-off of fish populations which may also be associated with more generalized mortality of aquatic life.University of Florida. Gainesville, FL (200 ...

s (Saville-Kent, 1888). Australian grayling killed in these events are described as being covered in "''cottony growths''", a characteristic hallmark of the alien fungus-like oomycete '' Saprolegnia parasitica''; these kills likely mark the arrival of this alien pathogen in Australian freshwater habitats via the importation, culturing and stocking of alien salmonid (trout) 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 P (1996). Overview of the Impacts of Introduced Salmonids on Australian Native Fauna. Australia Nature Conservation Agency, Canberra. https://www.dcceew.gov.au/environment/invasive-species/publications/impacts-introduced-salmonids-australian-native-fauna

Australian grayling is threatened by a number of factors. Dams and

weir A weir or low-head dam is a barrier across the width of a river that alters the flow characteristics of water and usually results in a change in the height of the water level. Weirs are also used to control the flow of water for outlets of l ...

s block

migration Migration, migratory, or migrate may refer to: Human migration * Human migration, physical movement by humans from one region to another ** International migration, when peoples cross state boundaries and stay in the host state for some minimum le ...

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. Alien

trout Trout (: trout) is a generic common name for numerous species of carnivorous freshwater ray-finned fishes belonging to the genera '' Oncorhynchus'', ''Salmo'' and ''Salvelinus'', all of which are members of the subfamily Salmoninae in the ...

species threaten grayling through predation and competition. Scientific studies have shown native fish species similar in habitat and lifestyle such as spotted galaxias are severely depressed in number in rivers inhabited by alien trout species (Ault & White 1994), and are forced into sub-optimal feeding locations, feeding times and diets by aggressive competition from alien trout species. A chronic lack of alien-trout-free habitat reserved for galaxias, grayling and other native fish species in south-eastern Australia generally is a major concern. Two Australian grayling were observed in the Glenelg River in south-western Victoria in early 2021, the first recorded sighting since 1899. Scientists think that some of the

environmental degradation Environment most often refers to: __NOTOC__ * Natural environment, referring respectively to all living and non-living things occurring naturally and the physical and biological factors along with their chemical interactions that affect an organism ...

caused after

agriculture Agriculture encompasses crop and livestock production, aquaculture, and forestry for food and non-food products. Agriculture was a key factor in the rise of sedentary human civilization, whereby farming of domesticated species created ...

was introduced into the area was being reversed, and the health of the river and

estuary An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime enviro ...

has improved enough for the fish to make a comeback. Australian grayling are listed as a vulnerable species under Australia's ''

'' and under the

IUCN Red List The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is an inventory of the global conservation status and extinction risk of biological ...

. There are now a number of conservation measures focused on conserving the fish.

Reproduction

Angling

Historical declines and current threats

References

Further reading