Crayfish plague is killing crayfish in Czech rivers: conservationists urge anglers not to spread the disease on their gear

An outbreak of crayfish plague — a disease that is almost always fatal to native crayfish species — has been confirmed in the Svinенský stream in southern Bohemia. According to the Czech Anglers' Union, infected crayfish lose coordination and die within a few days.

The disease is caused by the crayfish plague pathogen (Aphanomyces astaci), a microorganism that resembles both a fungus and an algae. "It's something halfway between a fungus and an algae, and it only affects crayfish," explained Jiří Marek, director of the South Bohemian branch of the Czech Anglers' Union. The pathogen attacks the animals' tissue and nervous system.

The main carriers of the disease are invasive North American crayfish species — the spiny-cheek and signal crayfish — which are themselves resistant to the plague but spread it among native fauna. "Wherever such a crayfish appears, mortality among native species reaches almost one hundred percent," Marek noted. Earlier outbreaks in southern Bohemia were recorded on the Blanice River near Husinec and at Lipno.

Major outbreaks were discovered in late June by the Nature and Landscape Protection Agency in the Iron Mountains area — on the Chrudimka River between the Křižanovice and Práčov dams. Dead crayfish were also found by residents of the village of Svídnice in the Pardubice Region.

On 26 June, the State Veterinary Administration introduced emergency measures on the Chrudimka River, which flows through Svídnice, to halt the spread of the infection. A protection zone has been established on the river and its tributaries, restricting the movement of people and animals as well as certain activities. Information boards have been placed at access points to the affected areas, and compliance is being monitored by the veterinary service.

Experts warn that people themselves often spread the disease — for example, on damp fishing gear. "It's enough for someone to stop fishing, leave a wet net in the basement overnight, and then head to another body of water the next morning. Pathogenic spores can survive in the net," Marek said.

Another source of infection is good intentions. "People often find a crayfish in a drying-up stream and, wanting to save it, move it somewhere else — say, to another river basin — out of kindness. But it could well turn out to be an invasive American species," said Jiří Bureš, director of the South Bohemian branch of the Nature and Landscape Protection Agency.

A scout camp is located near the site where the crayfish died in southern Bohemia — the children were given detailed instructions on how to behave if they encounter a crayfish in the stream. "Enjoy watching it. It's best not to touch it or move it anywhere," Marek advised.

To prevent the disease from spreading to other bodies of water, experts from the Nature and Landscape Protection Agency recommend following four basic rules: do not move crayfish to other locations; disinfect and sun-dry any items that have come into contact with water in affected zones; do not transport fish or other aquatic animals from infected waters; and do not release non-native crayfish from aquariums into natural water bodies. These rules are worth following even where crayfish plague has not yet been confirmed.

Scientists are also collecting data on sightings of native and invasive crayfish species — findings can be reported through the BioLog app to the nature observation database.

Read also: 8 best swimming spots near Prague: lakes, quarries and beaches within an hour's drive of the capital

Around Prague, based on reporting by ct24.ceskatelevize.cz