People Dump Goldfish In Australian River and Destroy the Habitat

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People Dump Goldfish In Australian River and Destroy the Habitat

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Many people around the world had at one point in their lives or another an aquarium and some fish in their homes. Goldfish are among the most common species of fish people have as pets. But once they get tired of them, and especially with changing the water in the aquarium, they then decide to do the human thing and give those fish another chance at life by releasing them in rivers or lakes.

Not many of these people think that their fish might actually stand a chance out there, but at least they think that at worst, their once favourite pet will make a tasty meal for some other fish. But they could not be more wrong because once released in the wild, these goldfish can be a big hazard for the local ecosystem and they can grow quite a lot.

For instance, goldfish were introduced into Australia’s Vasse River some 12 years ago, and since then there’s been a huge increase in their numbers. As you might expect, this wasn’t some natural event, but rather, their former owners were dumping them there. This caused them to become an invasive species which is now negatively impacting the local ecosystem.

“Perhaps they were kids’ pets where the family have been moving house and their parents, not wanting to take the aquarium, have dumped them in the local wetlands,” lead researcher Stephen Beatty from Murdoch University in Perth, said for ABC News.

“Unfortunately, a lot of people don’t understand that wetlands connect up to river systems and introduced fish, once they get in there, can do a lot of damage to native freshwater fish and the aquatic habitat.”

15 wild goldfish were tagged by the team near Busselton and then tracked their movements for over one year to see what happens. The findings showed that the fish move much faster that they previously believed, swimming to wetlands in order to spawn.

“Our research discovered the fish displayed a significant seasonal shift in habitats during breeding season, with one fish moving over 230 kilometres during the year,” said Beatty.

The thing about goldfish is inconspicuous at first, but if released into a river they will grow as mush as the resources available will allow them to.

Weighing in at 2 kg, you could call it resource-full.
Weighing in at 2 kg, you could call it resource-full.

And by available resources, we’re referring here to other fish, since goldfish are carnivorous.

“They cruise along the bottom stirring up the substrate with their feeding strategy, this can re-suspend nutrients into the water column which exacerbates things like algal blooms,” said Beatty. “They can also disrupt aquatic plants and eat other fish’s eggs.”

What’s more, these goldfish have already introduced at least new strain of disease in the rivers, something which is directly responsible for the decline in the number of native fish. This trend hasn’t only happened in Australia, though. Similar devastating effects have been seen in the US, in Colorado, where a lake had been infested with over 3,000 koi carps who spawned there after a local dumped a few of them nearby. Lake Tahoe in California has seen something similar, and so did Canada.

Koi carps, another invasive species dumped by owners, can grow to 8kg and up to one metre in length in the Vasse River.
Koi carps, another invasive species dumped by owners, can grow to 8kg and up to one metre in length in the Vasse River.

 

The full paper, “First evidence of spawning migration by goldfish (Carassius auratus); implications for control of a globally invasive species” has been published in the journal Ecology of Freshwater Fish.