First report of crayfish plague in Cherax quadricarinatus (von Martens, 1868) reared in Sicily.

Sporadic mortalities of redclaw crayfish Cherax quadricarinatus were registered in a Sicilian Crayfish facility in October 2011. Red swamp crayfish Procambarus clarkii reared in a separate tanks at the same facility did not experience any losses. Twelve moribund specimens of C. quadricarinatus with evident signs of infections were sent to the CISS of the Messina , for diagnostics investigations. At necropsy diseased crayfish showed loss of appendices with brownish pigmentation of stumps and melanised ulcers on exoskeleton. After gross examination, fresh tissue samples from eight crayfish were obtained for microscopic evaluation and histology. Four specimens were sent to the IZS delle Venezie for histological and bio-molecular analyses. The observation of fresh samples showed hyphae with several round zoosporangia. In histological sections serpiginous lesions were evident in the cuticle and aseptate hyphae in the hypodermis were associated with hemocytic infiltration and melanin deposition. PCR and sequencing analyses confirmed the suspicion of crayfish plague, identifying the oomycetes as Aphanomyces astaci. According to the literature this is the first report of aphanomycosis in farmed redclaw. The role of P. clarkii as asymptomatic carrier of the disease must be seriously taken into account. After the epidemic plague incidence, the farm owner decided to wipe out all crayfish present in the facility, carefully disinfecting the tanks, before restarting the production of P. clarkii.