Fungal infections in allochthonous freshwater crayfish in northern Italy.

A mycological study, involving Aphanomyces astaci, was carried out on allochthonous freshwater crayfish, which are increasing in number in the streams of Northern Italy. A. astaci is the agent of the crayfish plague a disease which has devastated many European native populations of freshwater crayfish. It appears that this disease is endemic to North America and that the higher resistance of the North American species is a result of the coevolution of both the fungus and the host. The North American crayfish carry this fungus as a chronic infection in melanized spots in their cuticle. Small pieces of the exoskeleton of 12 specimens of red swamp crayfish Procambarus clarkii (Girard), coming from the canals of the province of Bologna, and of 2 signal crayfish Pacifastacus leniusculus (Dana), coming from the Auenbachl stream in the province of Bolzano, were placed in plates containing glucose-yeast extract agar with penicillin and oxolinic acid and incubated at room temperature. Fusarium spp. was recovered from a total of 9 crayfish of the above-mentioned species; it was most frequently isolated from brown lesions of the exoskeleton (Burn spot disease). Dictyuchus sp was isolated from cottonwool-like tufts in one P.clarkii. An oomycete with morphological characteristics resembling A. astaci was found in one specimen of red swamp crayfish. The role played by fungi in the pathologies of freshwater crayfish is briefly discussed.