Giant Goldfish Demonstrate Why Not To Release Pets Into The Wild

One of the goldfish found in the Vasse River. Murdoch University.

Who knew something as little as a goldfish could turn out to be so destructively big? Well, researchers in Western Australia, actually, who have been studying the impact of goldfish dumped by pet-owners into the waterways of Australia for the past year.

Researchers at Murdoch University in Perth have discovered goldfish growing up to 30 centimeters (12 inches) and weighing up to a kilogram, with the largest tipping the scales at 1.9 kilograms (4.2 pounds), in the Vasse River in the southwest of Western Australia.

In a paper published in the journal Ecology of Freshwater Fish, Dr Stephen Beatty and his team studied the little-known habits of the invasive species in a bid to better understand and control them.

Thought to have been released into the waters by pet-owners, goldfish are one of the word’s worst invasive aquatic species. In the wild, they can grow to the size of a football, destroying the habitats of native fish by stirring up sediment from the riverbed, uprooting plants, introducing diseases, and competing with native populations, putting them and their ecosystem under pressure.

They also eat pretty much anything, including other fish eggs. Essentially, the freshwater fish can’t win when goldfish are around.

“Once established, self-sustaining populations of alien freshwater fishes often thrive and can spread into new regions, which is having a fundamental ecological impact and are major drivers of the decline of aquatic fauna,” explained Dr Beatty in a statement.

Using acoustic transmitters, similar to those used to track sharks, attached to 15 goldfish, the team followed their subjects for 12 months. They found that the goldfish traveled great distances, with one recorded as moving over 230 kilometers (143 miles) in a year.

Up until now, little has been known about the movement patterns of goldfish in the wild, making it hard to form an effective control program.

“The results of this study will have important direct management implications, enabling more strategic development of effective control programs for the species such as targeting migratory pathways,” Beatty said.

Needless to say, Beatty and his team are hoping their findings will act as a deterrent for people who think that dropping their fish off in the nearest waterway is a quick and harmless way of getting rid of an unwanted pet. It’s really not.

Speaking to Perth Now, Beatty said: “The key is really preventing it and getting the message out there that people shouldn’t be releasing freshwater fish in artificial wetlands." 

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