Self-cloning marbled crayfish are now prohibited in Michigan

Recent addition to Michigan’s prohibited species list makes marbled crayfish illegal to possess live.

Marbled Crayfish
Marbled crayfish have a distinctive streaked or marbled coloration pattern on their back. | Photo by Ranja Andriantsoa

Marbled crayfish (Procambarus virginalis), sometimes referred to as marmokrebs, self-cloning, or virgin crayfish, have the potential to become an aquatic invasive species in Michigan. Their tolerance for a wide variety of environmental conditions and diverse diet make them ideal for aquariums but also candidates for invasion if they are released into the wild. What makes them unique and especially concerning is that they are parthenogenetic (i.e, can self-clone). All marbled crayfish are female, and each one can lay up to 700 unfertilized eggs that develop into genetically identical offspring. Similar to other invasive crayfish, marbled crayfish are aggressive and could quickly outcompete native crayfish dominating lakes, ponds, and streams. They are omnivores and feed on algae, plants, snails, and amphibians.

They were first discovered in an aquarium in Germany in the 1990s and have no native range. They are likely the product of two distantly related members of the same crayfish species. Since their discovery, they have become increasingly popular in the aquarium industry. No marbled crayfish have been discovered in the wild in the U.S.; however, there are established populations in Europe, Asia, and Africa likely from aquarium releases or the live food trade. They are banned in the European Union as well as Idaho, Missouri, Tennessee, and now Michigan. Marbled crayfish are recognized by the Great Lakes and St. Lawrence Governors and Premiers as a “least wanted” aquatic invasive species that presents an imminent threat to the Great Lakes-St. Lawrence River region.

Marbled crayfish are one of four prohibited or restricted crayfish species in Michigan. Red swamp crayfish (Procambarus clarkii), rusty crayfish (Orconectes rusticus) and yabby (Cherax destructor) all have regulations that limit or prohibit their possession, introduction, importation, sale, or offer for sale as a live organism. Organisms that are not native or naturalized in the state and can either cause human or environmental harm or lack effective management controls, can be listed as prohibited or restricted by the Michigan Department of Natural Resources (MDNR) and the Michigan Department of Agriculture and Rural Development. Restricting or prohibiting possession helps prevent future introductions of invasive species and protects Michigan’s natural resources.

To comply with the new invasive species order, marbled crayfish must be disposed of and tanks should be thoroughly cleaned to assure no eggs or young remain. Sellers of marbled crayfish, even to locations out of the state, are required to comply with this regulation. The MDNR recommends owners of marbled crayfish review the American Veterinary Medical Association’s Guidelines for Euthanasia of Animals: 2020 Edition which provides recommendations for humane disposal of crayfish. Methods include submerging them in clove oil, ethanol, or other anesthetics. If that is not feasible, freezing crayfish for an extended period (> 48 hours) is also a euthanasia method.

Flushing marbled crayfish, or any aquatic animal, down a drain or toilet is not humane and may not necessarily kill the animal. It is never safe to release any aquarium plant and animal into the environment, even if they appear to be dead. Knowingly releasing marbled crayfish or other non-native species into the wild is prohibited by law.

Marbled crayfish get their name from the marmorated coloration of their carapace, or back. Their coloration is dependent on diet and water chemistry. Generally, in aquariums they appear blue due to color enhancing food. In the wild their colors range from olive to dark brown. When mature they are typically 3 to 4 inches long. They look somewhat similar to native white river crayfish and calico crayfish. Additional identification information can be found on the Michigan Department of Natural Resources invasive species website.

Any suspected sightings of marbled crayfish in the wild should be reported immediately to the MDNR. Photographs, location, and time are helpful for the DNR when determining the possibility of a sighting. If feasible, capture the crayfish and place it in a container in a freezer. Sightings should be reported to Lucas Nathan, MDNR aquatic invasive species coordinator, at 517-284-6235 or

Michigan State University Extension works collaboratively with the MDNR, Department of Agriculture and Rural Development, and Department of Environment, Great Lakes, and Energy to raise awareness of aquatic invasive species in the pet and garden trade through the Reduce Invasive Pet and Plant Escapes (RIPPLE) program. To learn more preventing invasive aquarium organisms in Michigan visit the RIPPLE website. State law requires all businesses and individuals offering live, non-native aquatic organisms for sale in Michigan to register and report annually with MDNR.

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