The ornamental fish trade is growing worldwide and Southeast Asian countries exporting numerous fish species for European countries. Exported fish is susceptible to several parasite species, including the digenetic trematode Centrocestus formosanus. With this study we present the results of a health monitoring focused on C. formosanus detected in ornamental fish imported in Italy during 2018 and 2019.
Generally, major losses in aquarium industry are caused by viral, bacterial, and fungal infections. However, metazoan parasites also can cause economic losses. In many cases, mortality may not be caused directly by parasite infestation, but by secondary infections. Centrocestus formosanus (Trematoda: Heterophyidae) is a digenetic trematode. This parasite has been found in the gill of numerous fish species especially from several Asian countries. The life cycle of C. formosanus is complex. The definitive host is a piscivorous birds or a fish-eating mammal, while the first intermediate host is a snail. Several fish species can act as second host. Infection of C. formosanus induces pathological changes in the gill filaments that envelops the metacercarial cysts. Gill infection results in structural and functional damage caused by a hyperplasia of the epithelial cells and fusion of the secondary lamellae. Infections are associated with mortality, decreased feeding rate and increased susceptibility to bacterial diseases. In the last years an increasing number of diagnostic tests for the detection of fish pathogens permit to improve sanitary control. C. formosanus is a potential zoonotic parasite that could cause epigastric pain and indigestion accompanied by occasional diarrhea. Several cases of human cases have been reported in Asia.
During 2018 and 2019 we performed a health monitoring on 46 batches of ornamental fish species imported from Singapore, Thailand and Israel with the aim to detect Centrocestus formosanus. Gill were investigated under a microscope to check the mature metacercariae (with X-shape excretory bladder). A total of 8 examined ornamental fish (17,40%) were infected with metacercariae of C. formosanus. The highest prevalence was found in Carassius auratus, followed by Xiphophorus spp. and Colisa lalia. The role live fish trade in the in the translocation of new parasites in sites previously free is a problem of major concern worldwide. For this reason, it is important to adopt quarantine and monitoring measures to avoid public health issues. This study highlights the necessity to improve the veterinary inspection on ornamental fish to avoid the widespread of exotic parasites, especially in Carassius spp. species used to supply lakes and domestic aquarium.