In The Wild, Goldfish Turn From Pet To Pest

Two decades ago, someone dropped a handful of pet goldfish into a creek in southwestern Australia. Those goldfish grew, swam downstream, mucked up waters wherever they went and spawned like mad, taking over the whole river. Researchers believe this scenario is caused of a feral goldfish invasion in Vasse River. Since 2009, they have been running a control programme that involves catching goldfish and freezing them to death. Despite this, goldfish in the Vasse are thriving, with some growing as long as 16 inches and weighing up to four pounds.

Goldfish are one of the world’s worst invasive aquatic species. Goldfish in the Vasse River, though, have the fastest known growth rate of goldfish in the world. They are an ecological nightmare. Goldfish swim along the bottom of rivers, uprooting vegetation and releasing nutrients that trigger algal growth. They transmit exotic diseases and parasites. Females produce up to 40,000 eggs each year and are capable of interbreeding with other species of wild carp. With no natural predators, a large portion of goldfish offspring survive to reproductive age, continuing a cycle of rampant over population.