Occurence of the pathogen Psorospermium haeckeli (Hilgendorf) in astacid populations in Croatia

Abstract

Psorospermium haeckeli is a thick-walled unicellular organism widely reported in European astacid crayfish. It is typically referred to as a "parasite" although its pathogenic impact remains unclear. Until now there were no data about its presence in Croatian astacid crayfish. We examined 144 specimens of the three astacid species from 12 different locations and found sporocysts of Psorospermium in 13 preparations of epidermal connective tissue of Astacus astacus and Astacus leptodactylus. Preparations were made by scraping the epidermal-connective tissue from under the carapace, treating it with 10% KOH and viewing it under a microscope at 125x, 250x and 400x magnification. A relative scale was used to describe the degree of infection of the crayfish by Psorospermium. We found two types of mature sporocysts and also some developing stages of Psorospermium. In the A. leptodactylus we found many sporocysts that were fully melanised. Further investigations are needed to understand the distribution of infected crayfish in Croatia and patterns of their infection with Psorospermium.