Attack of the clones: Sperm-stealing Prussian carp threaten to overwhelm Alberta waterways

Schools of Prussian carp — a sperm-stealing fish capable of cloning itself — are invading Alberta waterways, says an Edmonton researcher. 

The discovery of wild goldfish the size of dinner plates in a St. Albert storm pond is just the latest appearance of invasive fish in rivers and lakes across the province.

• Alberta city guts ponds of invasive 'monster' goldfish

A genetic cousin to the invasive Asian goldfish, Prussian carp have been fished out of waterways from the Red Deer River to the Bow River.

Deep-bodied and plump, Prussian carp are similar to common goldfish and often mistaken for them. But the Prussian  species has an important distinction from other freshwater fish.

'They're all clones'

"This might be a little shocking, but males are not actually needed for reproduction for this species. This is a bit unusual in the fish world," said Mark Poesch, a researcher and assistant professor with the University of Alberta's faculty of agricultural, life and environmental sciences.

"The females can reproduce clonally. They can clone themselves over and over and over again."

The carp can reproduce through a process called gynogenesis, making each individual fish a carbon copy.  This process requires "stolen" sperm found floating around in rivers and lakes, said Poesch.

"The females lay the eggs and actually take sperm from another species, so another species will fertilize the eggs but they won't actually contribute any genetic material," he said.

"This allows them to reproduce in huge numbers. It also means that all the individuals, and we've done some preliminary genetic work, they're all clones. They're all identical to one another."

The silvery fish have been captured in the Bow, Red Deer, and South Saskatchewan river basins in the past decade.

Government officials have made a concerted effort to encourage recreational fishing of Prussian carp, but populations continue to proliferate.

'Reproductive interference'

The fish are voracious plant eaters and their presence can deplete resources, causing native species to fight for food and space.

There are also concerns around "reproductive interference" with native species, Poesch said.

"They're taking the sperm from another species, and so that sperm is not going to fertilize their own eggs, so they're really taking advantage of this unique reproductive system," he said.

"They're here, they're having negative impacts, and they could actually overwhelm the system."

The hardy specimens spawn in huge numbers and can live up to 10 years.

• Giant goldfish multiplying in Alberta ponds 

How the fish, native to eastern Europe and parts of Asia, came to Alberta remains a mystery, but Poesch believes the fish may have been released by unwitting pet owners from backyard ponds.

Currently, there are no established eradication efforts in place for Prussian carp in Alberta other than recreational fishing and capture, and many conservationists fear this won't be enough to eradicate them.

"Goldfish are found throughout the province and people do release them. And we think that's how this little guy got in here and now they're really starting to take over," said Poesch.

"We think they first came here in 2000 and the reason it took so long to find them is that people misidentified them as goldfish.

"They first arrived in Medicine Hat and since then, we find them all the way up to the city of Red Deer, and they are literally everywhere."

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