Murray hardyhead  (Craterocephalus fluviatilis)

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

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).

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).

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).

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). 

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).

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 about the Murray hardyhead:

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