The Goldfish is a well-known species of fish that has been sold world-wide for use in aquariums, ponds, and water gardens for hundreds of years. Native to eastern Asia, Goldfish were first kept as pets in China around the year 960 and have been reared and sold as pets ever since. They are commonly thought to be the first foreign fish species to be introduced to North America from overseas. Goldfish are often illegally released by people who no longer want them.
In Ontario, Goldfish are usually found in the wild in quiet areas of populated urban or suburban vegetated ponds, streams, and pools. Goldfish are able to tolerate fluctuations in water temperature and water with low levels of dissolved oxygen. They feed mainly on fish eggs, fish larvae, and aquatic plants. In healthy ecosystems, Goldfish do not appear to compete well with some native fish. However, they are quite tolerant of poor water quality, as such, may threaten some native species in degraded ecosystems.
Goldfish have been introduced worldwide. They are established in locations throughout each province of Canada and all of the United States, except Alaska. In Ontario, established populations have been reported along the north shore of Lake Erie, the west end of Lake Ontario, and occasionally in other locations across the province.
For an up to date distribution map of Goldfish in Ontario, visit www.EDDMapS.org/distribution.
Impacts of Goldfish
The ecology and impacts of Goldfish introduced to North America’s waters have not been widely studied. However, the behaviour of Ontario populations indicates they may reduce the province’s biodiversity through their effects on native species.
- Goldfish eat snails, small insects, fish eggs, and juvenile fish, making this species a competitor with, and predator of, native fish.
- They stir up mud and other matter when they feed, which increases the cloudiness of the water and affects the growth of aquatic plants.
- They have the potential to produce large populations in some situations, especially in stagnant waters with few predators.
- Goldfish can carry diseases, such as the Koi herpesvirus that can harm local fish populations.
How to Identify Goldfish
- Goldfish have elongated bodies, averaging 12 to 22 cm long, but can grow up to 40 cm long.
- Their colour can vary from the typical bright orange to olive green or creamy white. Wild populations are typically olive to gray.
- Head and eyes are large, relative to the rest of the fish.
- The dorsal fin is long and has a single stout spine with a serrated trailing edge, similar in shape to that of the Common Carp’s dorsal fin. The anal fin is short and has a single stout serrated spine, as well. The tail is deeply forked.
- The mouth is small and has no trailing whiskers (barbels), not to be confused with the Common Carp, which does have barbels.
What You Can Do
- Learn how to identify Goldfish and how to prevent accidentally spreading this invasive species.
- Don’t release any live fish into Ontario lakes, rivers, or streams. Return or donate unwanted aquarium fish to a pet store or local school.
- Clean, Drain, Dry your boat, trailer, and equipment after each use. Remove all plants, animals and mud before moving to a new waterbody.
- If you’ve seen a goldfish or another invasive species in the wild, please contact the toll-free Invading Species Hotline at 1-800-563-7711, visit EDDMapS, or search for the ‘Invasive Species in Ontario’ project on iNaturalist.org to report a sighting.
OFAH/OMNRF Invading Species Awareness Program. (2021). Goldfish. Retrieved from: www.invadingspecies.com.
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Header photo by Ontario Federation of Anglers and Hunters