Minnesota state: When goldfish become a plague

They were once small goldfish that lived in aquariums somewhere in Minnesota, USA. Then they were dumped in the lake – and got bigger and bigger. Now they are devastating biotopes and endangering drinking water.

After reading this post, you might find yourself eyeing small goldfish in the aquarium with a certain amount of discomfort. The fish in question look like large, orange-red dented soccer balls. They are approximately 46 cm long and weigh less than two kilograms.

“These are not mutants of fish,” says researcher Chelsey Blanke. And that’s reassuring. Chelsey takes care of the ecosystems of the many lakes in Minnesota. First her team got ten of these golden chunks out of the water, later another 18, and now they are appearing more and more often.

“They keep getting bigger all the time”

“Many fish species have what is known as ‘eternal growth’. That means that the goldfish keep getting bigger and bigger,” says Blanke. “That depends of course on the environment: the good water quality and healthy sources of food. The goldfish taste better fish eggs from other fish than food flakes from the can. And they have no natural enemies – the native species do not eat goldfish.”

From the perspective of ex-pets, these are paradisiacal conditions. But less for all other living beings. Especially since goldfish can theoretically live up to 50 years. They even manage to go without oxygen for days. In freedom they act like a pack of wild boars, because contrary to what their glamorous name suggests, they prefer to dig for food down in the sea mud.

“You use it to stir up the sediment layer, the dirt and also the clay,” explains Blanke. “There are nutrients in this mud, and once they are stirred up it changes the quality of the water.”

“Difficult to get her out of the lakes again”

It is not just the drinking water quality that suffers, says Blanke. The fish also uproot aquatic plants with their burrowing, and they eat young animals of other fish species. They devastate the biotopes and it is very difficult to get them out of the lakes again. That’s why it shouldn’t get that far in the first place.

That means, if you want to release Little Goldie from the fishbowl into freedom, you should give it away as a present or give it away in online exchanges. But never tip into a body of water. It is astonishing that in Minnesota goldfish as an invasive species have so far been little researched – very different from other pests such as rats or tiger mosquitoes. That is why studies to combat them are only now beginning.

“When they are there, it gets really complicated”

Blanke explains: “We have to carefully weigh up and try out what works against the goldfish – without harming other species. One possibility would be to empty the affected lakes – not a real option here. You could fish them out, but that’s enormous exhausting and very expensive. And then the pesticides, but they would also kill native fish species. Once the goldfish are there, it gets really complicated. ”

How about a culinary solution? Since goldfish are part of the carp family, why not think about just eating them, right?

“That is conceivable,” says Blanke. “I know countries that are trying this out with other invasive fish species. You don’t eat goldfish here, but you would have to develop a marketing strategy for that. It’s definitely an interesting idea.”