Parasites and endobiotic fungi in digestive gland cryosections of the mussel Mytilus galloprovincialis in the Northern Adriatic, Croatia

Histology has been used in the past to investigate the effects of diseases and parasite infections in native mussel populations that are often used as sentinel species in coastal environmental monitoring and as stock in mariculture. This paper presents the first study of parasite diversity using cryosections of the Mytilus galloprovincialis Lamarck, 1819 digestive gland. Mussels were sampled across the annual cycle at two sampling sites: St. Andrew and ACI Marina in the Northern Adriatic (Croatia). The protozoan of the genus Nematopsis Schneider, 1892 (Apicomplexa, Gregarina) was detected in digestive tubules, while the turbellarian (Urastomidae) Urastoma cyprinae von Graff, 1913 was found in the connective tissue at the edge of the digestive gland. The filamentous fungus Alternaria sp. (Fungi, Ascomycota) was detected in epithelial cells of the digestive tubule in cryosections. Nematopsis sp. occurred with the prevalence ranging from 20 to 100%, and the intensity of infection in less than 30 oocysts in most of the cases. U. cyprinae was detected in mussels sampled at St. Andrew and had a prevalence of 20% in September. Conidia of Alternaria sp. were found in mussels sampled at St. Andrew in September and November. Cryosections provide a useful and affordable means for monitoring parasites and endobiotic fungi.