First detection of Aphanomyces astaci and its potential responsibility for mass mortalities of Pontastacus (Astacus) leptodactylus in Greek lakes

Aphanomyces astaci is a pathogen categorized among the 100 worst invasive alien species, responsible for the crayfish plague disease. In the past, many disease outbreaks devastated native European crayfish populations. The pathogen was transferred in Europe by its natural carriers, among which is the North American crayfish species Pacifastacus leniusculus, that has been introduced in Greece during 1980s. On the other hand, Pontastacus leptodactylus represents an indigenous species in Greece and apart from being keystone organism constitutes a valuable food source. Here, we investigated populations from lakes Volvi, Polifitou and Vegoritida for the pathogen’s presence after the mass mortalities observed from local fishermen in the two of them, namely, Vegoritida and Polifitou. All samples from these two lakes were positive, verifying the pathogen presence for the first time in Greece. On the other hand, all examined Pacifastacus leniusculus individuals were surprisingly negative, despite the expected hypothesis that they could be the reason for the spread of the pathogen in Greece. The unfavorable environmental conditions observed this year in combination with the improper management practices may led to massive reduction of crayfish populations in lakes Vegoritida and Polifitou. Thus, there is an urgent need for deeper investigations to unveil the leading cause of the disease outbreak in order to design and propose proper management measurements