Identification and Reproduction

Identification:

• Goldfish are a popular aquarium fish and come in a wide range of sizes, shapes and colourations.  
• They have elongated bodies, typically 12 to 22 cm long but can reach up to 40 cm long.
• Their colour can vary greatly, ranging from bright orange to olive green or creamy white. Wild populations are often a combination of olive, grey and black.

• Head and eyes are large.
• They have a long dorsal fin with a single stout spine with a serrated trailing edge. The anal fin is also stout with a single serrated spine. 
• Tail is deeply forked. 
• The mouth is small and has no trailing whiskers (barbels).

Reproduction:

• Female will release eggs after an aggressive chase by the male goldfish.
• Like all cyprinids, goldfish eggs are sticky and will adhere to substrate and plants. 
• After the eggs are attached, the male will fertilize the eggs by releasing milt.
• The fertilized eggs will hatch in 2-5 days.
• Young will attach themselves to aquatic plants for several days while they absorb their yolk sac.

Habitat & Ecology

• Goldfish in the wild are usually found in quiet areas of vegetated ponds, streams and pools, often in populated urban or suburban areas. 
• The fish are able to tolerate fluctuations in water temperature and water with low levels of dissolved oxygen.
• They are quite tolerant of poor water quality, and may threaten some native species in degraded ecosystems.
• Goldfish are omnivores, meaning they will eat both plants and other animals, and they will grow according to the size of water body they are placed in. 
• They are established in all provinces and states across Canada and United States except Alaska. 

Impacts

• Goldfish eat snails, small insects, fish eggs and young 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 natural growth of aquatic plants.
• Goldfish do not have any predators in the introduced habitat.
• They have the potential to produce large populations under optimal conditions. 
• These invaders have also been known to predate on eggs, larvae and even adult native fish.
• Goldfish can carry diseases such as koi herpesvirus that can harm local fish populations. Koi herpesvirus is not a risk to human health, but it is never safe to consume fish that may have this disease. 

Management

• Do not release live goldfish into wild environment.
• Return or donate unwanted aquarium fish to a pet store or a local school. 
• With no natural predators goldfish pose a risk to native fish species in the B.C. Interior.
• The most effective way to control goldfish is the use of physical control. 
• Inspect your boat, trailer and equipment after each use. Remove all plants, animals and mud before moving to a new waterbody.

Photo Credit: Pete Wise. Goldfish taking over a pond in the North Okanagan

Resources

For more details on the background and impacts of goldfish check out Ontario's Invading Species Awareness Program here.

Refer to the Aquatic Invaders of the Pacific Northwest; Carassius auratus auratus (Common Goldfish) for more infomation on the history and invasion of goldfish. 

For more information check out the Invasive Species Compendium datasheet on Carassius auratus auratus (common goldfish).

Download BC's Invasive Species Alert for Goldfish here. 

Header photo (USGS).