The noble pen shell (Pinna nobilis, L, 1758.) is an endemic species and the largest bivalve in the Mediterranean Sea, which can grow up to 120 cm in length (Vazquez M. et al., 2017.). Since 1992, according to the Directive adopted by the European Council, it has been placed on the list of endangered and protected species. By filtering and retaining organic matter, it contributes to the clarity of sea water and has an important ecological role (Basso et al., 2015.). P. nobilis is distributed at depths from 0.5 m to 60 m in areas where marine flowering plants are present and on sandy bottoms (Marrocco et al., 2019.). In the Adriatic Sea, over 600 areas were recorded where noble pen shells could be found, and by the spring of 2021, all places were affected by mass mortality (Katsanevakis et al., 2021.). Research has shown that a parasite from the genus Haplosporidium and bacteria from the genus Mycobacterium are involved in the pathogenesis of mass mortality (Šarić et al., 2020.). Sea currents are thought to have contributed to the faster spread of the pathogen. The pen shell population continues to decline, due to the presence of Haplosporidium pinnae and other pathogens in the environment (Katsanevakis et al., 2021.).