Photo: Gunther Schmida

Introduction

Goldfish were originally imported into NSW as an aquarium fish. Over many decades they have become widely distributed throughout lowland rivers.

Goldfish are related to carp and feed mostly on small shellfish and plant material. They survive in still and sluggish water and can tolerate relatively high temperatures and low oxygen levels. Goldfish spawn in summer. A large fish can lay several hundred eggs which hatch in about a week. They are thought to be a common food source for some predatory freshwater fish such as Murray cod and spangled perch.
Size: Commonly to 200 mm, can reach 400 mm

Impacts on native fish

Despite being related to carp, little is known about the impact goldfish have on native fish, particularly in regard to competition for food, resources and habitat. Few detrimental effects have been recorded, however, this may be due to limited research.
One impact that has been well recorded is the transmission of disease.
Disease
Goldfish ulcer disease (GUD) is a bacterial disease first isolated from a goldfish farm in Victoria in 1974. Since then outbreaks have occurred at warm water fish hatcheries in NSW and Victoria. NSW DPI researchers have found that fingerlings of Murray cod, golden perch and silver perch are resistant to GUD. However, there has been one recorded outbreak of the disease in a silver perch fish farm in NSW. Trout are at high risk of infection.

What can we do?

Some well-established alien species are difficult to control. However, there are some options for their management and improving the odds for native fish.

Environmental management and rehabilitation
Management of issues such as water quality, environmental flows, fish passage and snags can maintain or return conditions to those that best suit native fish. This improves the ability of native fish to compete and creates conditions less suitable for alien species.

Restricting the spread
The spread of alien species has often been associated with their use as bait. For this reason, use of live fish bait is now illegal in NSW. Improved education is also needed to avoid the accidental release of these species.

Biological control
Biological control utilises methods such as introduction of a natural predator or parasite, manipulation of the immune system or genetic material and sterilisation to control or remove an unwanted species. These controls can be effective but are often technically difficult, expensive and require detailed testing to ensure that controls won't impact on other species.

Disease
Diseases such as viruses can effectively manage alien species. However, it can be difficult to find a species specific disease that will not affect other fish.

If you find what you believe is a goldfish (or another species which you suspect is not native to the area), freeze it whole and Report it!

References and further reading

Harris, JH and Gehrke, PC (eds). 1997. Fish and Rivers in Stress. The NSW Rivers Survey. NSW Fisheries Office of Conservation and the Cooperative Research Centre for Freshwater Ecology in association with NSW Resource and Conservation Assessment Council.
Rowland, SJ and Ingram, BA. 1991. Diseases of Australian native freshwater fishes with particular emphasis on ectoparasitic and fungal diseases of Murray cod (Macullochella peelii peelii), golden perch (Macquaria ambigua) and silver perch (Bidyanus bidyanus). Fisheries Bulletin 4. NSW Fisheries.
Young, WJ. (eds) 2001. Rivers as Ecological Systems: The Murray-Darling Basin. Murray-Darling Basin Commission. Canberra.