Invasive zebra mussels found hiding in aquarium plants for sale at pet stores

Vigilant pet retailers can prevent invasive species from spreading.

hand holding glass with moss ball inside. Moss ball contains one zebra mussel on it.
Infested moss balls may be sold as large balls or separated and repackaged in smaller containers at retail stores. | Photo credit: Amanda Smith

An observant employee at a Seattle Petco recently discovered zebra mussels in a shipment of Marimo moss balls which are popular in fish aquariums and are sometimes used as houseplants. The employee reported their findings in the United States Geological Survey Nonindigenous Aquatic Species database, alerting aquatic invasive species managers across the United States. Since the initial report, dozens of states have reported zebra mussels in moss balls available for sale at popular pet retailers including in Michigan. The products have since been removed from retail shelves. While invasive zebra mussels are now common in many waterbodies in Michigan, they still pose an invasion risk here, and are far less common in the western United States.

Do you have a moss ball in your aquarium?

Not all aquarium moss balls need to be discarded. However, because the infested moss balls have been distributed across the United States, you should inspect the contents of your aquarium for zebra mussels. Zebra mussels are striped and measure less than two inches in size. They attach to any hard surfaces such as metal, glass, plastic, stone, wood or rocks. They are extremely resistant to cold temperatures and many chemicals. Under state law, zebra mussels cannot be possessed alive in Michigan, so contaminated moss ball products must be disposed of properly.

If zebra mussels are found on any moss balls in containers or in aquariums, infested moss balls and packaging should be frozen for 24 hours, boiled for one full minute, or submerged in bleach or vinegar for 20 minutes before double-bagging, sealing and disposing in the trash. The Michigan Department of Natural Resources also recommends that tank water from aquariums holding infested moss balls be decontaminated by removing plants and pets, adding 1/10 cup bleach to every gallon of water and allowing at least 10 minutes of contact time before draining.

Discoveries of zebra mussels in retail stock or in household aquariums must be reported to the state. Reports should be made to Lucas Nathan, DNR Aquatic Invasive Species Coordinator at You can also use this contact information for assistance with inspection or proper disposal.

Retailers also serve as a trusted source of information for consumers and are typically the first to be contacted by a hobbyist looking to surrender an unwanted aquarium. In effort to educate retailers and hobbyists of invasive aquatic organisms, Michigan State University Extension in partnership with the Michigan Invasive Species Program developed the Reduce Invasive Pet and Plant Escapes (RIPPLE) campaign. RIPPLE educates consumers and retailers about proper containment and disposal of aquatic plants and fish.

When you clean or dispose of aquariums, keep the following RIPPLE recommendations in mind. Remember, it is never safe to release aquarium water or its contents into waterways:

  • Inspect and rinse new aquatic plants to rid them of seeds, plant fragments, snails and fish.
  • Seal aquatic plants for disposal in a plastic bag in the trash. Do not compost.
  • Give or trade unwanted fish or plants with another hobbyist, environmental learning center, aquarium or zoo.
  • Contact a veterinarian or pet retailer for guidance on humane disposal of animals.

To learn more about the national response to this developing issue visit this website.

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