The first record of Aspidogaster conchicola (Trematoda: Aspidogastridae) in the freshwater mussel Unio pictorum in Croatia

Although Aspidogaster conchicola is a common and widespread parasite of freshwater molluscs, knowledge about its distribution and hosts in Croatia is still insufficient. The aim of our research was to investigate the presence of A. conchicola in the freshwater mussel Unio pictorum, which is widely distributed in the rivers of Europe. The study was conducted in the Mrežnica River, where U. pictorum is a common species. Five specimens of U. pictorum were collected by scuba diving in October 2021. The dissection of mussels was carried out in the laboratory, and all tissues were inspected under a stereo microscope. Determination of the parasite was performed based on the number and arrangement of alveoli. The results showed that the prevalence of infection was 40% (two out of five mussels were infected), and the intensity of infection was 2 to 3 specimens per mussel. All parasites were detected in the mussels’ pericardial cavity. In conclusion, this is the first record of A. conchicola in U. pictorum in Croatia.