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Zebra mussels: WGFD discovers invasive mollusk in pet store moss

by Wyoming Livestock Roundup

            “Zebra mussels, an incredibly invasive mollusk species native to Russia, have recently been found in pet stores across the nation,” says Wyoming Game and Fish Department (WGFD) Director Brian Nesvik during a WGFD Facebook Live on March 10. 

            “Zebra mussels are a freshwater mussel,” explains Alan Osterland, WGFD chief of fisheries. “This species is native to Russia, and they are very small – about the size of a fingernail.”

            Recently, zebra mussels have been found throughout Petco stores located in Cheyenne, Rock Springs, Gillette and Casper, Nesvik shares. The invasive species has been found on moss balls, a common decoration in aquariums sold in pet stores.

Severity of mussels

            Zebra mussels have a detrimental impact on ecosystems and municipal water systems. 

“We have spent millions of dollars and countless amounts of manpower in effort to prevent zebra mussels from entering the state,” he adds. “The consequences of mussels being introduced to sewer systems, or worst case, introduced into live water – creeks, rivers, lakes or ponds – will be devastating.”

Nesvik explains when zebra mussels reproduce quickly, they attach themselves to pipes and dams. The mussels continually grow and encrust themselves to other mussels. It essentially causes a mass which is costly to clean up.

            “In one year, a female can produce one million eggs,” shares Osterland. “The larvae are microscopic and the human eye can’t see them. Even as adults they can be small and hard to detect.”

“This is a significant find. We have worked hard for years to prevent these from showing up. We have been successful to date, so this disappoints us. We are working hard to mitigate potential impacts this will have and we are trying our best to prevent problems,” Nesvik says.

Marimo balls

            Marimo balls, the moss balls zebra mussels have been identified in, are clumps of green algae. They have several names such as betta balls, betta buddies, shrimp buddies and moss balls. 

            Marimo balls are packaged several different ways. Often, the moss is dehydrated and most products are imported from different countries.  

            The WGFD found most of the infected marimo balls have been found in Petco stores.

            “There are several different places where it’s been packaged,” notes Osterland. “However, about 90 percent of the infected moss balls are imported to California then further distributed from there. We believe the infected moss balls came from southern Ukraine.”

Osterland encourages people to not take the risk and dispose of any moss balls and aquarium water with specific instructions as to prevent the spread of zebra mussels.

Disposing moss balls

Aquarium items and dirty water should never be dumped down the drain.

“When disposing of marimo balls, WGFD recommends boiling them for five minutes on the stove,” Osterland shares. “After boiling it, it can be thrown in the garbage.”

He notes, disposing aquarium water which contained a marimo ball is much like disposing the marimo ball itself. 

“Boil the aquarium water for five minutes,” Osterland explains. “Then dump the water on your lawn or in a plant. WGFD asks aquarium water not be dumped down the drain or toilet.”

Actions taken

            The WGFD is taking several steps to prevent invasion of zebra mussels. 

“We want to err on the side of caution,” Nesvik says. “If someone has dumped aquarium water down the drain, we ask them to call WGFD. They are welcome to call the Stop Poaching Hotline located on the home page of the website if they wish to stay anonymous.”

He adds WGFD needs to know where to watch for zebra mussels. They will investigate possible areas for any zebra mussels. 

According to Osterland, it is hard to detect if an aquarium is infected because the zebra mussels may be in the larvae stage.

Impacts to water supply

            Thousands of people rely on municipal water systems. Mistakenly dumping aquarium water down the drain could affect many people.

            “Everybody has ties to water,” Nesvik states. “This needs to be acknowledged because the zebra mussel can impact the delivery and the quality of water. We are all reliant on water, so this invasive species could disrupt everyone.”

Nesvik adds, zebra mussels can also have an impact on power generation, irrigation and ponds and lakes.  

            “We are doing everything in our power to prevent invasion of zebra mussels,” Nesvik states. “However, these mussels are impossible to eradicate during this time.”

            WGFD, alongside federal agencies, are working to determine how widely spread the zebra mussels are. They have been in contact with Petco and Petsmart headquarters to get moss balls removed from shelves. 

Madi Slaymaker is the editor of the Wyoming Livestock Roundup. Send comments on this article to

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