Invasive Species Alert: Zebra Mussels in Aquarium Moss Balls (November 2021)

We have been notified recently through the Department of Oceans and Fisheries (DFO) that moss balls infested with Zebra Mussels were detected in September 2021 at the U.S international borders. We are working to determine the situation in Canada. At this time in Canada, the DFO is working to send reminders to importers, distributers, and retailers about the serious threat these invasive mussels pose to Canada and their obligations under our Aquatic Invasive Species Regulations.

If you have any questions, please email


From:National AIS / EAE national (DFO/MPO) <DFO.NationalAIS-EAEnational.MPO@DFO-MPO.GC.CA>
Sent: november 22, 2021 09:01 AMTo: National AIS / EAE national (DFO/MPO) <DFO.NationalAIS-EAEnational.MPO@DFO-MPO.GC.CA>Subject: Importations de boules de mousse / Importations of moss balls


As you may recall, moss balls (i.e., Marimo balls, Cladaphora balls, Betta Buddy, Aegagropila linnaei decorative algae balls) infested with invasive Zebra Mussels were detected for sale across Canada and the United States in March 2021. In Canada, Zebra Mussels are a prohibited species under the federal Aquatic Invasive Species Regulations. In response to their detection, directions were issued by Fisheries and Oceans Canada’s Fishery Officers and/or provincial and territorial enforcement officers to temporarily postpone the importation and sale of moss balls.

 Many of the directions issued by Fisheries and Oceans Canada and provincial and territorial governments have expired, meaning the importation and sale of moss balls may resume. However, American federal authorities once again detected infested moss balls entering the United States containing Zebra Mussels in September 2021. Given the interconnectedness of the supply chain across North America, this suggests the risk of contaminated moss balls may remain high for Canada.

We would like to remind you that retailers that purchase and sell moss ball products are responsible to report any unexpected species to the appropriate authorities. It is your responsibility to know and comply with import and other requirements under federal, provincial and/or territorial legislation. In some cases, this may include requirements under more than one act and/or regulation. Your actions are vital towards protecting Canadian waters from the threat of aquatic invasive species.

The expectation from federal, provincial, and territorial regulators is that all moss ball products are free from aquatic invasive species. As such, Fisheries and Oceans Canada and our provincial and territorial partners will continue to monitor for compliance with the Aquatic Invasive Species Regulations and pursue violations to the full extent of our abilities. Federal Fishery Officers and/or provincial and territorial enforcement officers may conduct site visits to your locations and/or take other measures to verify compliance.

Failing to comply with the Aquatic Invasive Species Regulations may result in a fine not exceeding one hundred thousand dollars and, for any subsequent offence, a fine not exceeding one hundred thousand dollars or imprisonment for a term not exceeding one year. This does not preclude additional charges, fines, and other legal outcomes from provincial and/or territorial aquatic invasive species laws and regulations (see Appendix A for more information).

Should you have any questions regarding the above information, please contact your local authority for aquatic invasive species.

Susan Roe
National Manager for Aquatic Invasive Species | Gestionnaire Nationale pour les espèces aquatiques envahissantes
Biodiversity Management | Gestion de la biodiversité
Fisheries and Oceans Canada | Pêches et Océans Canada
Ottawa, Ontario  K1A 0E6


Below you will find more information on zebra mussels, how to dispose of any contaminated moss balls and clean aquarium environments.

Zebra mussels (Dressena Polymorpha), which are regarded as one of the most troublesome invasive species in North America. Zebra mussels are small, fingernail-sized mollusks native to the Caspian Sea region of Asia. They have three life stages: larval, juvenile, and adult. In the larval stage, the mussels live freely in the water column, where they can be easily transported. Adult zebra mussels can stay alive for several days outside of water and commonly attach to boats, fishing equipment and aquarium plants. In spite of their small size, zebra mussels clog pipelines used for water filtration, render beaches unusable, and damage boats. They also negatively impact aquatic ecosystems by harming native organisms

Note that these guidelines are preliminary or provisional and are subject to revision. If you have any questions please contact your province’s governing body for aquatic invasive species or your local pet store for expert advice on the tank restarting process

We recommend that you take the following steps with all moss ball aquatic plant products:

1) Decontaminate the moss ball using ONE of the following methods, ensuring that the disposal method you choose is in compliance with provincial and animal welfare regulations:

• Place the moss ball into a sealable plastic bag and freeze for at least 24 hours, OR

• Place the moss ball in boiling water for at least 1 full minute, OR

• Submerge the moss ball in chlorine bleach, diluted to one cup of bleach per gallon of water, OR Submerge the moss ball in undiluted white vinegar for 20 minutes.

2) Once step 2 is complete, place the moss ball and any of its packaging in a sealed plastic bag and dispose in the trash.

3) If vinegar, boiling water, or bleach was used, the liquid can be disposed down a household drain—never down a storm drain where it could enter and damage local waterways.

If the moss ball was placed in an aquarium, please take these additional steps:

1) Collect any fish or other living organisms and place them in another container, with water from a separate, uncontaminated water source.

• Test the pH and temps of the new water and the water the fish came from. Fresh tap water can be dramatically different from an established tank especially if the tank has turned more acidic over time.

• For ALL city water add a dechlorinator to the new water before adding the fish to the temporary holding container.

• Add an air stone in the temporary container so they do not suffocate during the process.

• Ways to reduce stress in the holding container include:

o Adding clean plastic plants that can just float around

o Keeping the animals in a low light area

o Separate overly aggressive fish into a separate holding container

2) Sterilize the contaminated aquarium water by adding ¼ teaspoon bleach for each gallon of water. Let the water sit for 15 minutes and then dispose of the sterilized water down a household drain.

3) Clean the aquarium and accessories using one of the following methods, ensuring that the disposal method you choose is in accordance with manufacturer recommendations:

• Boiling Method:

o Use water that is 140 degrees F to flush and coat the tank and all accessory surfaces, OR

• Disinfection Method:

o Make a disinfection solution using 1/3 cup of bleach per gallon of water.

o Soak the aquarium, substrate, rocks, décor, and filter media in the bleach water solution for 15 minutes.

o Rinse off all items prior to setting up the aquarium.

4) Re-establishing the tank:

• Dispose of the previously used filter media and replace with new media.

• Use a dechlorinating product to neutralize any residual chlorine prior to reintroducing aquatic life.

• Add commercially available aquarium bacteria starter to replace all the beneficial bacteria that were removed during this process.

• It is recommended that you do another water change within a week and continue to monitor the tank for any unusual or unexpected aquatic life.

If you find any zebra mussels please make a report via
Brendan Spearin, AIS Regional Coordinator 
M: 204-290-6586
Fisheries and Oceans Canada | Freshwater Institute

We will follow up as more details become available.