Due to its traits, this crustacean native to North America is considered the most invasive crayfish in Europe and is included on the so-called Union list of invasive alien species. The discovery was made at Lake Milada in the Ústí nad Labem Region. Specialists from NCA CR subsequently confirmed the presence of the species at the site.

"During a weekend ride, cyclists noticed a single crayfish and remnants of claws on the path and sent us a photograph. Upon arriving at the site, our fears were confirmed – several red swamp crayfish were successfully captured directly from Lake Milada. The discovery of this intruder is not good news for our native environment. In addition to competing with domestic crayfish species, the red swamp crayfish carries crayfish plague. This fungus-like pathogen poses a fatal threat to our native crayfish," says Tomáš Görner from the Nature Conservation Agency of the Czech Republic.

The red swamp crayfish (Procambarus clarkii) reaches lengths of up to 15 cm. It is most frequently black and red in colour, though whitish or blue forms can occur rarely. Its typical features include prominent spines and tubercles on its narrow claws. It originates from the south-eastern United States and northern Mexico. It was introduced to Europe (Spain, France, Italy) in the 1970s for aquaculture (meat production) but escaped into the wild. It has also been popular as an ornamental aquarium species.

The red swamp crayfish is currently found in approximately 20 European countries and, due to its characteristics, is considered the most invasive alien crayfish species in Europe. In 2016, it was placed on the Union list of invasive alien species, which prohibits breeding, trading, and releasing this species. Despite this, it was likely illegally released into Lake Milada by an irresponsible hobbyist.

The red swamp crayfish reproduces rapidly, reaching sexual maturity in its first year of life. Females can produce up to two clutches per season, and their egg production is significantly higher than that of our native crayfish species. It achieves high population densities, posing a threat to local populations of small invertebrates, which serve as its food. Red swamp crayfish also graze heavily on vegetation. They compete with our native crayfish for food and habitats, can survive in poorer temperature conditions, tolerate pollution better, and thrive relatively well even out of water.

"The critical step now is to attempt some technically feasible isolation of the newly discovered population and, above all, to prevent the further spread of the red swamp crayfish. We therefore urge the public to refrain from releasing these invasive crustaceans into the wild under any circumstances. We also welcome reports of potential sightings of this crayfish species in other locations via email at invaznidruhy@aopk.gov.cz. We would also like to thank everyone who sends us information regarding the occurrence of invasive plant and animal species," adds Tomáš Görner.

Four invasive species of North American crayfish have now been confirmed in Czechia: the signal crayfish, spiny-cheek crayfish, marbled crayfish, and red swamp crayfish.

Photo Lenka Čolobentičová