What Ontario is doing

To prevent this unwanted invader from coming into the province, Ontario has regulated marbled crayfish (Procambarus virginalis) as a prohibited invasive species under the Invasive Species Act, 2015.

Learn about the Invasive Species Act and regulations.


The marbled crayfish, also known as marmokrebs, is an invasive crayfish which is suspected to have been created accidentally within aquariums.

It is an all-female species which reproduces through clones that are genetically identical to the mother without the need for sperm or a fertilized egg.

They are found to survive in many different environments, including countries with climates like Ontario.

Marbled crayfish are relatively popular in the aquarium trade, which provides the main source of spread to new areas through release into local waterways.

Because the marbled crayfish does not require sexual reproduction, a new population can become established in new area with the release of only one individual.


The marbled crayfish was first discovered in the German aquarium trade in the mid 1990s and has since become established in many locations across the country.

Since then, this species has been released and is established in nine European countries, as well as Madagascar and Japan.

There are no known occurrences of this species in Ontario.

View an up-to-date distribution map of this species in North America.

Impacts of marbled crayfish

Marbled crayfish can outcompete small native aquatic species for food and habitat.

Their generalist diets can lead them to overconsume aquatic vegetation, reducing available habitat and food sources.

Overconsumption of invertebrate and fish eggs may negatively impact food availability, disrupting food webs and Ontario’s recreational and commercial fisheries.

Abundant numbers of these crayfish may also destabilize shorelines through the creation of their burrows on riverbanks.

How to identify marbled crayfish

  • A medium-sized crayfish is 3 to 10 cm in length.
  • Body can be dark brown, tan, brown-green or sometimes blue, always with marble patterning.
  • Juveniles develop spotted pigmentation and possess more marble patterning in adolescence.
  • Between the legs under the crayfish there is a sperm receptacle, known as the annulus ventralis. It is a flat and bell-shaped structure that can differentiate marbled crayfish from other species.

What you need to know

  • Learn how to identify marbled crayfish and how to prevent the introduction or spread of this animal through the aquarium trade.
  • It is against the law to import, possess, deposit, release, transport, breed/grow, buy, sell, lease or trade marbled crayfish in Ontario.
  • Never buy, keep or breed marbled crayfish as a pet or for any other purpose. They may be listed under synonyms such as marble crayfish, self-cloning crayfish or marmorkrebs.

Reporting illegal activity

If you have any information about the illegal importation, distribution, or sale of marbled crayfish, report it immediately to either:

If you’ve seen marbled crayfish or another invasive species in the wild, please:


Pictures showing a general view of a specimen of marbled crayfish collected in the semi-natural ponds in Băile Felix, Oradea, Romania (A), a close up of the Annulus ventralis (B), and carried stage two juveniles (C). Photo by A. Togor (A, C), L. Pârvulescu (B). 

Marbled crayfish specimen (A), close up of the Annulus ventralis (B), and carried stage two juveniles (C) (From Togor et al. 2017)