Lockdown goldfish being released into the wild are harming native species

The popular pet breeds quickly and can survive in cool water

The popular pets have a hearty appetite and can thrive in various conditions. Getty

Goldfish bought as pets during lockdown are putting other species at risk after their owners released them into the wild, an ecologist has told The National.

Dr James Dickey, of Queen’s University Belfast, said the species has a “voracious” appetite and can thrive in several types of water.

“They will happily eat aquatic invertebrates, small fish, amphibians and aquatic vegetation,” he said.

“Also, their method of feeding, whereby they lift lots of particles into the water column, affects the clarity of the water, affects competition with other species and can lead to algal blooms. They’ve also been shown to decrease their visibility to predators by doing this and even regulate water temperature. In our study, the goldfish were absolutely voracious.”

Dr Dickey, who was lead author of the study published in NeoBiota, added: “They were shown to have more ‘bold’ behaviour, known as a dispersal enhancing trait, suggesting they could expand their range quite quickly if released. We propose that this behaviour, combined with high feeding rates and availability, is a perfect storm.”

Pet owners releasing unwanted animals into the wild is a known problem, but was probably exacerbated by the pandemic.

While many believe this is a humane option, new research suggests that attempting to ‘save’ the life of a goldfish could in fact lead to catastrophic outcomes for native biodiversity.

Invasive species are one of the leading causes of global biodiversity loss, and the pet trade is responsible for a third of all aquatic invasive species, according to Queen’s University Belfast.

To understand the ecological risks posed by species within the pet trade, the researchers focused on the two fish most commonly traded in Northern Ireland: goldfish and the white cloud mountain minnow.

Now globally popular, the goldfish was first domesticated over a thousand years ago and has since established non-native populations around the world. The white cloud mountain minnow, on the other hand, is a species with a limited invasion history to date.

The study showed goldfish consumed much more than the white cloud mountain minnow or native species. In terms of behaviour, goldfish were also found to be far braver, a trait linked with invasive spread.

Regarding the scale of the problem, Dr Dickey said: ”This is highly topical, with huge increases in the numbers of pets bought over lockdown. With life slowly returning to normal, it may be that owners are beginning to regret their lockdown purchases, be it for reasons of size, cost, reproductive rates or time and effort. It is often quite difficult to get rid of a pet once you have it. Pet stores may take them back but they are under no legal obligation to do so, leaving owners reliant on finding someone to take them off their hands.”

While northern European climates are often a barrier to non-native species surviving in the wild, goldfish are known to be tolerant to such conditions, and could pose a real threat to native biodiversity in rivers and lakes, eating up the resources that other creatures depend on.

“Our research highlights that goldfish are high risk, but we hope that the methods developed here can be used to assess others in the pet trade across Ireland and further afield,” he said.

“Readily available species are most likely to be released, so limiting the availability of potentially impactful ones, alongside better education of pet owners, is a solution to preventing damaging invaders establishing in the future.”

The research led by Queen’s University Belfast was presented at the International Conference on Aquatic Invasive Species, held in Ostend, Belgium.