Goldfish Infestations in Thompson-Nicola Lakes


Goldfish (Carassius auratus) are popular family pets, but when they are released into the natural environments of North America, they become invasive species with a highly competitive and adaptable nature.

Goldfish infestations are a growing problem in the Thompson-Nicola Watershed, and the invasive species is outcompeting many native species in the region causing concern for the survival of native fish populations. According to iNaturalist, goldfish infestations have been spotted in Kamloops, White Lake Provincial Park area and Salmon Arm.


Physical Description

While there are over 100 species of goldfish, most people recognize the species as small, orange fish with wide eyes and rounded fins, but historically, they have not always looked this way. Native to China, the goldfish is a relatively small member of the carp family. They originally had greyish-silver or olive-green scales, and any goldfish with a bright orange colour was considered a prized ornamental fish and was selectively bred for thousands of years. As a result of this selective breeding, the majority of Goldfish people see today have this bright orange colour.

The size of a goldfish completely depends on their environment. In aquariums, the species can grow up to approximately 2.5-15cm (depending on how large the aquarium is), but when released into the wild, goldfish have been known to grow up to 38cm. The largest goldfish to be found in the wild was 59 cm!


Goldfish have an omnivore diet and forage far and wide for any sort of food available to them. A goldfish’s diet consists of fish eggs, fish larvae, insects and aquatic plants. Goldfish become considerable competition to native species that rely on these foods, and they also become a predators to all kinds of fish eggs and fish larvae, including ones of their own kind.

Like their relatives, the minnow and the carp, the goldfish’s eating habits increase turbidity, the cloudiness in water due to suspended material, in the bodies of water they live in. Turbidity is heightened by goldish because when they eat, they forage through the sediment at the bottom of the waterbody to search for food. This foraging causes excess movement of sediment material, and the native aquatic plants in the environment suffer from lack of light due to this movement.


Goldfish are very adaptable creatures that can live in a variety of environments, but they prefer streams, ditches, ponds and lakes with abundant aquatic vegetation. In the Thompson-Nicola Watershed, goldfish in the wild are found in ponds close to city centers and popular recreation sites where they have been released by people nearby.

These adaptable creatures are known to be extremely resilient when it comes to low oxygen and temperature levels in their environments. Goldfish have a special enzyme that turns metabolic products into alcohol when oxygen levels drop (similar to a brewer’s yest). In fact, goldfish can survive up to 5 months only relying on this alcohol. This means that unlike native fish that may die under frozen lakes in the winter, goldfish can survive through these winter months making them more likely to become an infestation in as little as a year.

Image: FreckLes, iNaturalist CC-BY-NC


Goldfish reproduction happens when the female’s eggs are released onto nearby plants or rocks where they are then fertilized by the male. A goldfish’s eggs are quite sticky making them resistant against the water current. Goldfish can lay up to thousands of eggs at once, but some may be left unfertilized or eaten by adult fish.

Female goldfish can also reproduce without male fertilization through a process called gynogenesis. In this process, the female can receive sperm from another species of minnow or carp, and as a result, the female goldfish clones itself creating a rapid population increase.

After being fertilized, the eggs will hatch anywhere between 2 to 7 days afterwards, depending on water temperature. When hatched, the fry survive on algae, but are often preyed on by other fish, including their own species. The lifespan of a goldfish, in ideal conditions, can be up to 30-40 years, outliving many native species that may be living in the water body.


Currently, goldfish are not listed as an invasive species under the Federal Aquatic Invasive Species Regulations in Canada, but it is federally prohibited to release any non-native aquatic species into the wild. The following are ways in which people can individually stop the spread of the species in BC’s waterways:

  • Don’t let it loose! Instead of releasing an unwanted pet goldfish into the wild, consider contacting the retailer to consider returning your pet, give the fish to a pond owner, or donate your fish to a local aquarium or school.
  • Raise awareness to avoid spread of goldfish into BC water bodies.
  • If you see goldfish in the wild in British Columbia, please report the sighting to ISCBC.

Additional Resources