Pet goldfish released into UK waters are turning into monster 2ft killing machines

Pet goldfish released into UK waters are turning into monster 2ft killing machines

Pet goldfish released into the wild are wreaking havoc on native species, according to new research.

Once out of the aquarium tank and let loose in open waters, they can turn into fat two-foot long ‘giants’ .

They gorge on insects and tadpoles – outcompeting rivals and threatening biodiversity.

Taking the ‘humane option’ by attempting to save the family favourite may lead to catastrophic consequences for the planet.

Lead author Dr James Dickey, of Queen’s University Belfast, said: “Our research suggests goldfish pose a triple threat.

“Not only are they readily available, but they combine insatiable appetites with bold behaviour.

“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.

Goldfish are generally quite small, but can grow to up to two-feet long in the wild
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Getty Images)

“They could pose a real threat to native biodiversity in rivers and lakes, eating up the resources that other species depend on.”

They also contribute to poor water quality by mucking up the bottom sediments and uprooting plants.

Invasive species are one of the leading causes of global loss. The pet trade is responsible for a third of all aquatic invasive species.

Owners releasing unwanted animals into the wild is a major problem. The goldfish is popular across the world – often awarded to children as a prize at funfairs.

It was first domesticated over a thousand years ago and has since established non-native populations around the world.

The Northern Ireland team compared the pet to the white cloud mountain minnow – a species with a limited invasion history to date.

They assessed the ecological impacts and risks of potential pet trade invaders based on availability, feeding rates and behaviour.

Goldfish were found to be voracious – consuming much more than the white cloud mountain minnow or native species.

In terms of behaviour patterns, goldfish were also found to be much braver – a trait linked with invasive spread.

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

“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 findings in the journal NeoBiota follow appeals to aquarium owners in Minnesota to stop releasing pets into waterways after several huge goldfish were pulled from a local lake.

Officials in Burnsville, about 15 miles south of Minneapolis, said they can grow to several times their normal size.

As many as 50,000 goldfish were removed from local waters in nearby Carver County. They can easily reproduce and survive through low levels of oxygen during winter.

Goldfish could pose a real threat to native biodiversity in rivers and lakes if released in to the wild
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Getty Images)

Ecological destruction caused by aquarium pets is a growing phenomenon.

Carnivorous lionfish, native to the Indo-Pacific, were released by Florida pet owners after Hurricane Andrew in 1992.

They killed off dozens of Caribbean species – allowing seaweed to overtake the reefs.
Goldfish have received less attention than other invasive species.

But warnings have also been issued in Virginia and Washington state as well as Australia and Canada.

In 2013, Scientific American reported that researchers trawling Lake Tahoe netted a goldfish that was nearly 1.5ft long and weighed 4.2lb.

It’s estimated as many as 200 million goldfish are bred each year – most ending up on domestic display.

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