Crayfish plague Aphanomyces astaci detected in redclaw crayfish, Cherax quadricarinatus in Taiwan

• Crayfish plague, Aphanomyces astaci, infects crayfish on three continents.
• Redclaw crayfish, C. quadricarinatus, is highly susceptible to crayfish plague.
• This is the first report of redclaw crayfish naturally infected by A. astaci in Asia.
• The PCR/ISH technique was used to detect A. astaci.
• Crayfish plague studies should be done more in Asian aquaculture.

Between December 2013 and January 2014, five outbreaks of an unknown disease with moderate to high cumulative mortality were observed among the freshwater redclaw crayfish (Cherax quadricarinatus) populations at four crayfish farms in Miaoli and Changhua counties (northern Taiwan) and at one crayfish farm in Pingtung County (southern Taiwan). Polymerase chain reaction (PCR) analysis allowed the detection of Aphanomyces astaci DNA in dead crayfish. Histopathological examination revealed an infection of host tissue by fungal hyphae that presented as typical non-septate hyphae within the soft abdominal cuticle from the first to second segment and in the tail fan. In PCR assays completed for the detection of crayfish plague, an expected 568-bp product, specific for the A. astaci ITS gene, was obtained from all sub-adults and adults examined. In a comparison of our strains with the known strains of A. astaci in Europe, nucleotide sequence identities were very similar, with 99.8–100% sequence similarity in that gene region. Positive reactions to in situ hybridization, using a digoxigenin (DIG)-labelled DNA probe, further confirmed A. astaci as the causative agent. This is the first report concerning natural infection of A. astaci in freshwater redclaw crayfish in Asia.