Goldfish Invasion Threatens Native Fish Populations in Canada.
Natural rivers and lakes in Canada are under attack by giant goldfish discarded by pet owners, according to a report by CBC on March 4. While goldfish may seem harmless, this resilient species can grow to massive sizes over their long lifespans.
A goldfish caught at Hamilton Harbor, Canada. (Photo: Fisheries and Oceans).
There are many varieties of goldfish, all belonging to the carp family, sometimes hybridized with other species such as koi. For instance, a goldfish named Carrot in France weighs as much as a 10-year-old child. While Carrot lives in BlueWater Lakes, a recreational fishing site, wild goldfish thrive in freshwater environments, growing not only to large sizes but also reproducing at an astonishing rate, with females capable of laying about 150,000 eggs in a single year.
“Females can reproduce without males“, said Brian Heise, an associate professor in the Natural Resource Science department at Thompson Rivers University. “They have a special process called gynogenesis, where females receive sperm from a male fish to initiate egg development, even though the eggs are not fertilized.”
As their numbers and sizes soar, goldfish can devastate ecosystems, competing with native wildlife, spreading diseases, and harboring parasites that threaten wild species. Their preferred diet includes fish eggs, larvae, and aquatic plants. Their foraging behavior can stir up sediment, muddying the water and blocking sunlight from reaching underwater plants. For these reasons, scientists are concerned about the explosive growth of wild giant goldfish in the freshwater environments north of Vancouver, including Terrace, Quesnel, and Whistler. The Canada Invasive Species Centre advises the public not to release pet goldfish into the wild to protect the ecosystem.
The size of goldfish is partly limited by their habitat. Fish kept in small tanks with moderate food will remain small, partly due to stress. They will maintain that size until death. However, if the same fish is transferred to a larger tank with more food, it can grow significantly bigger.
