Murray hardyhead (Craterocephalus fluviatilis)

Description

Murray hardyhead fact file

• Description
• Biology
• Range
• Habitat
• Status
• Threats
• Conservation
• Find out more
• Glossary
• References
• Print factsheet

Murray hardyhead description

The Murray hardyhead (Craterocephalus fluviatilis) is a small, predominantly freshwater fish, with a moderately deep, translucent body which has a luminescent silvery sheen ^{(2) (3) (4) (5)}. The Murray hardyhead has a small mouth with a single row of teeth on each jaw ⁽⁵⁾.

Like other fish in the Atherinidae family, the Murray hardyhead has a characteristic slender stripe running across the length of its body, that can have a silver, golden, or reddish tint ^{(4) (5)}. The Murray hardyhead’s two dorsal fins are widely separated, the first being composed of numerous sharp spines, but the second having only one. The anal fin also has just one spine ^{(4) (5)}. The fins of the juvenile Murray hardyhead are a vivid orange. This colour, however, fades as the fish approaches adulthood ⁽³⁾.

Synonyms

Craterocephalus fluviatillis.

Size

Length at birth: 9 - 19 mm ⁽²⁾

Adult length: up to 75 mm ⁽²⁾

Murray hardyhead biology

Little is known about the biology of the Murray hardyhead. It is a highly mobile, schooling fish that is capable of speedy manoeuvres to avoid predators, and is often observed nipping quickly amongst aquatic vegetation in large schools ⁽⁴⁾.  

When feeding, the Murray hardyhead forages for tiny crustaceans over sand or silt flats ^{(2) (5)}. This species is, however, considered an omnivore as it is also known to eat some plant matter ⁽⁵⁾.

Murray hardyhead spawning is thought to occur from late spring to summer, when the female lays adhesive eggs among aquatic vegetation ^{(4) (5)}. The adult Murray hardyhead has a notably broad tolerance for changes in water salinity, and is therefore able to live in both freshwater and saltwater ⁽⁴⁾. 

Murray hardyhead range

As its common name suggests, the Murray hardyhead is endemic to the mid and lower-reaches of the Murray-Darling River system in south-eastern Australia ^{(2) (3) (4)}.  This species’ patchy range of isolated populations extends from Lake Alexandrina in South Australia to Yarrawonga in Victoria ⁽²⁾. This species is no longer present in New South Wales, which was once the northern part of its range ^{(6) (7)}.

Murray hardyhead habitat

This species is most commonly found in still or slow flowing waters such as temporary lakes, billabongs or river backwaters where salinity levels can fluctuate substantially ^{(3) (4) (5)}. In these environments it often inhabits open water and shallow sandy flats; however, it is most at home amongst aquatic vegetation in deeper waters ^{(3) (4) (5)}.

Murray hardyhead status

The Murray hardyhead is classified as Endangered (EN) on the IUCN Red List ⁽¹⁾.

Murray hardyhead threats

The most significant threat to the Murray hardyhead is the lack of water ^{(4) (6)}. Increasingly prolonged periods of dry conditions in the Murray-Darling basin have led to many important sites drying up or salinity levels becoming too high ^{(2) (4)}. The Murray hardyhead is now thought to be extinct in the New South Wales ⁽⁷⁾ and further population declines are predicted throughout the remaining range ⁽⁶⁾.

A further threat to this species lies in the reduction of connecting waterways between lakes and the Murray River channel, resulting in the isolation and extinction of local populations ^{(3) (2)}. The Murray hardyhead relies on such waterways for dispersal and recolonisation of new habitats ⁽⁵⁾.

In addition to this, water running through urban and agricultural land in the Murray-Darling basin can flush harmful chemicals, and nutrients that cause algal blooms, into lakes and rivers, having a negative impact on the populations of this species ⁽⁶⁾.

The Murray hardyhead is also faced with the introduction of invasive species, such as common carp (Cyprinus carpio) or perch (Perca fluviatilis). These species will either compete with the Murray hardyhead for food or predate on it directly ⁽⁷⁾.

Murray hardyhead conservation

The most significant threat to the Murray hardyhead is the lack of water ^{(4) (6)}. Increasingly prolonged periods of dry conditions in the Murray-Darling basin have led to many important sites drying up or salinity levels becoming too high ^{(2) (4)}. The Murray hardyhead is now thought to be extinct in the New South Wales ⁽⁷⁾ and further population declines are predicted throughout the remaining range ⁽⁶⁾.

A further threat to this species lies in the reduction of connecting waterways between lakes and the Murray River channel, resulting in the isolation and extinction of local populations ^{(3) (2)}. The Murray hardyhead relies on such waterways for dispersal and recolonisation of new habitats ⁽⁵⁾.

In addition to this, water running through urban and agricultural land in the Murray-Darling basin can flush harmful chemicals, and nutrients that cause algal blooms, into lakes and rivers, having a negative impact on the populations of this species ⁽⁶⁾.

The Murray hardyhead is also faced with the introduction of invasive species, such as common carp (Cyprinus carpio) or perch (Perca fluviatilis). These species will either compete with the Murray hardyhead for food or predate on it directly ⁽⁷⁾.

Find out more

Find out more about the Murray hardyhead:

• FishBase
  http://www.fishbase.org/summary/Craterocephalus-fluviatilis.html

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Glossary

Anal fin

In fish, an unpaired fin on the under surface of the fish, behind the anus.

Crustaceans

Diverse group of animals with jointed limbs and a hard external skeleton, characterised by the possession of two pairs of antennae, one pair of mandibles (mouthparts used for handling and processing food) and two pairs of maxillae (appendages used in eating, which are located behind the mandibles). Includes crabs, lobsters, shrimps, woodlice and barnacles.

Dorsal fin

The unpaired fin found on the back of the body of fish, or the raised structure on the back of most cetaceans (whales, dolphins and porpoises).

Omnivore

An organism that feeds on both plants and animals.

Spawning

The production or depositing of eggs in water.

References

1. IUCN Red List (August, 2011) 
   http://www.iucnredlist.org/
2. Ebner, B., Raadik, T., and Ivantsoff, W. (2003) Threatened fishes of the world: Craterocephalus fluviatilis McCulloch, 1913 (Atherinidae). Environmental Bioliolgy of Fishes, 68: 390.
3. Ebner, B. and Raadik, T. (2001) Murray hardyhead – Craterocephalus fluviatilis. Australian Society for Fish Biology Newsletter,31: 2.
4. Ellis, I. (2005) Ecology and Breeding Seasonality of the Murray hardyhead Craterocephalus fluviatilis (McCulloch), Family Atherinidae, in Two Lakes Near Mildura, Victoria. Murray-Darling Freshwater Research Centre, Albury.
5. Backhouse, G., Lyon, J. and Cant, B. (2008) Background and Implementation Information for the Murrray Hardyhead, Craterocephalus fluviatilis National Recovery Plan. Department of Sustainability and Environment, Melbourne. Available at:
   http://www.environment.gov.au/biodiversity/threatened/publications/recovery/murray-hardyhead/pubs/murray-hardyhead-background.pdf
6. Backhouse, G., Lyon, J. and Cant, B. (2008) National Recovery Plan for the Murray Hardyhead, Craterocephalus fluviatilis. Department of Sustainability and Environment, Melbourne. Available at:
   http://www.environment.gov.au/biodiversity/threatened/publications/recovery/murray-hardyhead/pubs/murray-hardyhead.pdf
7. Dixon, P. (2006) Proposed Determination – Craterocephalus fluviatils – Murray Hardyhead. Department of Primary Industries Fisheries, Nelsen Bay. Available at:
   http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0018/208215/PD-Hardyhead.pdf