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Eastern Freshwater Cod - Maccullochella ikei

by Gavin Butler and Andy Moore

Threatened Fish Profile – In Newsletter 31_1, May 2001

Photo: Andy Moore

Conservation status:

The eastern freshwater cod is currently listed as Endangered by ASFB (2000) and also appears on the IUCN red list, with an Endangered A1cd rating. Effectively, this denotes that the species is considered as facing a very high risk of extinction in the wild in the near future, having suffered an observed, estimated, inferred or suspected reduction in population size of at least 50% over the last ten years or three generations (IUCN, 2000). In response to these listings, legislation has been enacted under Commonwealth and NSW law to assist in protecting the species. However, a number of threatening processes still sustain pressure on residual stocks, including continuing anthropogenic related habitat and water quality degradation, invasion and introduction of exotic and non-endemic native fish species, as well as problems experienced by small, fragmented populations.

Description:

The eastern freshwater cod (Maccullochella ikei), sometimes called the Clarence River cod or east coast cod, is native to the Clarence and Richmond River of north-eastern NSW. A large percoid fish, M. ikei has been recorded up to 40 kg and over 1 metre in length. However, fish of this size are rare with most normally less than 700mm and 5 kg (Rowland, 1996). Similar in appearance to the Murray Cod (Maccullochella peelii peelii), the eastern freshwater cod is an elongate, deep bodied fish, yellow-green to golden in colour, with dark heavily reticulated mottling extending both dorsally and laterally along the length of the fish (Harris and Rowland, 1996). The ventral surface of most individuals is generally grey-white, with the dorsal, pectoral, caudal and anal fins all clear to dark grey-green with whitish margins (Harris and Rowland, 1996). The pelvic fin is generally colourless, with the distinctive extended filaments at the margins of the fin, white in colour.

Distribution and decline:

M. ikei were once widespread and abundant throughout both the Clarence, Richmond and Brisbane River catchments. However, during the 1920’s and 1930’s both populations underwent a dramatic decline, with the Richmond populations thought to be largely extinct by the late 1930’s. Large scale declines and localised extirpations were also experienced across much of the Clarence system, with only small extant populations persisting in isolated pristine habitats. A number of factors led to the decline of M. ikei, including overfishing, desnagging, siltation and eutrophication (Rowland 1993). These problems were further exacerbated by a number of mass fish kills in the late 1930’s, with many sub-populations completely decimated at this time.

Natural history:

While little is known of the specific biology and ecology of the species, M. ikei is assumed to prefer clear, slow flowing rivers or creeks, with rocky or gravel substrate and in-stream cover of rocks, timber or tussocks (Rowland, 1993; Rowland, 1996; Butler, 2000). The species is considered as the top predator throughout its range, making use of available cover to ambush passing prey for forage. This includes various water fowl, snakes, frogs, crustaceans as well as a range of fish species including their own young (Harris and Rowland 1996). Growth is slower than in Murray cod, with the eastern freshwater cod reaching only 445 mm and 1.3 kg at five years. The species is thought to reach sexual maturity at four to five years of age, spawning in September or October when water temperatures rise above 16⁰ C. Fecundity is generally considered as reasonably high, with upwards of 10,000 eggs recorded per female in captive breeding experiments (Rowland 1989).

Current research:

In response to the continued decline of M. ikei, a number of captive breeding programs have commenced since the late 1980’s. Initially this involved the release of 30,000 juveniles into 13 sites in the Richmond and Clarence Rivers in the late 1980’s, with a further 220,000 juvenile fish recently stocked between 1997 and 2001 (PBF 2000). However, there are concerns over the genetic effect that restocking may be having on the extant population. Research assessing the genetic affects of restocking is ongoing. Research using age and growth, mark recapture, and radio-telemetry is also underway and should provide a more complete ecological and biological profile for the species.

References:

Butler, G.L. (2000). Population Structure and Habitat Preference of the Eastern Freshwater Cod, Maccullochella ikei (Pisces: Percichthyidae) within the Mann-Nymboida Catchments, NSW. Resource Science and Management, Southern Cross University, Lismore. Integrated project. Unpublished.

Harris, J.H. and Rowland, S.J. (1996). Australian Cods and Basses. Freshwater Fishes of south-eastern Australia. R. McDowall. Sydney, Reed Books.: 150-163.

IUCN (2000). Red list of Threatened Animals Database [Online], Available: http://www.wcmc.org.uk/cgi-bin/arl-output.p [26/8/00].

PBF (2000). Project Big Fish: An initiative to save the Eastern Freshwater Cod. Coffs Harbour., Project Big Fish Inc.

Rowland, S.J. (1989). Fisheries Research: Conservation of the eastern freshwater cod. Grafton, Agricultural Research and Advisory Station.

Rowland, S.J. (1993). Maccullochella ikei, an Endangered Species of Freshwater Cod (Pisces: Percicthyidae) from the Clarence River System, NSW and M. peelii mariensis a New Subspecies from the Mary River System, QLD. Records of the Australian Museum. 45: 121-145.

Rowland, S.J. (1996). Threatened fishes of the world: Maccullochella ikei Rowland, 1985 (Percichthyidae). Environmental Biology of Fishes. 46: 350.