Episodes of mortality in white-clawed crayfish (Austropotamobius pallipes Complex) in three streams of Modena Province (Northern Italy)

As a consequence of massive and apparently total white-clawed crayfish mortalities occurred in Rossenna river (September 2004), Lerna stream (February 2005) and Rio Selve creek (June 2005) in region of Emilia Romagna (Modena province, Northern Italy), the causes of the disease outbreaks were investigated. In all the three streams the kill crayfish were in different state of preservation and only just died or moribund crayfish with or without apparent lesions were collected and submitted to mycological, parasitological, bacteriological, virological, and hystopatological analyses. In the rivers examined Extended Biotic Index (EBI) and chemical-physical and bacteriological water analyses were carried out. During the surveys, saprophytes, ectosymbionts and ectocommensal organisms were frequently observed in crayfish. No virus was found. Fusarium sp. was the most frequently isolated mycete and it occurred in pure culture from the specimens coming from Rio Selve creek. Furthermore Mucor sp. and Penicillium sp were detected on the crayfish from the Rossenna river, while Trichoderma sp., Alternaria sp., Gliocladium sp. and Mucor sp. from Lerna specimens. At Bacteriological investigation Hafnia alvei was isolated both from Lerna and Rio Selve samples, while Aeromonas hydrophila from Lerna. At the histology, all the crayfish showed severe fungal hyphae infiltrations of exoskeleton and superficial skeletal muscle through the hypodermis with inflammation and melanization. All water courses showed environmental pollution. A prolonged exposure to toxic substances in the water could have exhausted the defense mechanisms so that the crayfish were more susceptible to the action of opportunistic pathogenic agents and subsequently succumbed.