This study reports the presence of cartilaginous cysts in zebrafish gills, purchased at the end of 2012 before the application of the Italian Legislative Decree 26/2014 and used for experimental research. It highlights the importance of using specific pathogen-free organisms from reliable production establishments to avoid obtaining false results in experiments. Of 20 samples analyzed, 4 showed cysts in gills, with abnormal tissue modification and cartilaginous metaplasia induced by prolonged parasitic insult. The results obtained from the periodic health monitoring program showed the presence of metacercariae of digenean trematodes, specifically identified as Centrocestus formosanus.
Keywords: Centrocestus formosanus; cyst; metacercariae; zebrafish.