Reliable identification of crayfish plague is vital for Finland’s crayfish populations

July 2/2019

The Finnish Food Authority has discovered a previously unknown species of water mould in noble crayfish in a small Finnish lake, similar to that which causes crayfish plague. This water mould resembles crayfish plague, an invasive species in Finland, so closely that it may compromise the reliability of crayfish plague studies. The discovery of this new species shows that disease identification methods must be continuously improved to guarantee their reliability.

A Finnish species of water mould, Aphanomyces fennicus sp. nov., is so closely related in its genome to the water mould that causes crayfish plague, Aphanomyces astaci, that several of the molecular biology based methods developed for identifying crayfish plague are unable to tell the two apart.

“In this case, the diagnostics problem that was discovered by accident has already been solved, as a research method developed in Norway was improved further on the basis of this new information. The revised method is currently being tested in both Norway and Finland. The Kuopio unit of the Finnish Food Authority is the World Organisation for Animal Health's (OIE) reference laboratory for crayfish plague. Reference laboratories secure the reliability of disease diagnostics and assist other laboratories in identifying diseases”, says Chief Specialist, DVM (PhD) Satu Viljamaa-Dirks of the Finnish Food Authority.

Crayfish plague is an insidious disease

Crayfish plague grows in the crayfish cuticle, and an infection is usually fatal for the European crayfish.The disease infects crayfish and makes them ill in all seasons. The transmission risk is particularly great during crayfish fishing and crayfish relocation. Even noble crayfish may carry crayfish plague in a latent form, and in such a case the population will not recover even with restoration stocking.

Samples are important for crayfish research

Without samples, diagnostic methods cannot be developed and reliability assessments cannot be carried out.  

The Finnish Food Authority examines all submitted samples of dead crayfish free of charge and offers crayfish plague carrier detection for a fee. This summer an acute infection has been detected in two populations of noble crayfish, both from Eastern Finland.

“When there is a plan to restock a population of crayfish after it has been devastated by crayfish plague, the status of the waterway should always be surveyed in advance using test fishing and test caging. Carrier testingis performed on 60 crayfish using a molecular method. It is a good idea to contact the crayfish plague experts at the Finnish Food Authority when the stocking is being planned, so that the survey will be as reliable as possible”, says Viljamaa-Dirks.

The research findings on the new species were published in a peer-reviewed scientific article:
Viljamaa-Dirks, S., Heinikainen, S.  
A tentative new species Aphanomyces fennicus sp. nov. interferes with molecular diagnostic methods for crayfish plague. Journal of Fish Diseases 2019: Vol. 42, No. 3, pp. 413 - 422.    

Read a dissertation Epidemiology of crayfish plague.
Crayfish plague reference laboratory

Further information:
Chief Specialist Viljamaa-Dirks, tel. +358 (0) 44 720 1469