Diversity and Prevalence of Fungi Associated with Freshwater Crayfish in Three Regions of Lithuania: A First Assessment

Fungi play an important role in freshwater ecosystems, yet their diversity and distribution among crayfish species remain poorly understood. We analyzed the diversity of fungi in four crayfish species (Astacus astacus, Faxonius limosus, Pacifastacus leniusculus, and Pontastacus leptodactylus) collected across three regions of Lithuania: northeast, southeast, and west. A total of 27 crayfish were collected, and each crayfish was examined for muscle and hepatopancreas tissues. Of the 27 tested individuals, four crayfish were free of fungi. A total of 77 isolates of fungi were obtained from the hepatopancreas and muscle tissue samples of the examined crayfish using direct isolation. Combining phenotypic characterization with ITS sequencing, 28 fungal genera were identified, with Cladosporium, Fusarium, and Penicillium being the predominant genera. Fungi were more frequent in muscle tissue (81.5%) than in hepatopancreas tissue (66.7%), p = 0.219. A. astacus and P. leniusculus exhibited the highest prevalence of fungi, with 100% of individuals (n = 2). Regional diversity of fungi varied across regions, with Shannon diversity values ranging from H′ = 1.748 in the west to H′ = 3.076 in the southeast. These patterns suggest apparent host- and region-associated differences in crayfish fungal communities.