Tumours and tumour-like lesions in wild and farmed warmwater fish from Croatia

Fish oncology is especially useful in our understanding of neoplasia in general and is included in discussions of comparative oncology. The present study describes the occurrence of tumours and tumour-like lesions in wild and farmed warmwater fish in Croatia and provides data on their effects on individual fish, wild fish populations and aquaculture industry, with an emphasis on possible aetiology. A total of 12 specimens, representing 6 species of 6 families (Leuciscidae, Gobionidae, Cyprinidae, Siluridae, Ictaluridae, and Esocidae) were submitted to the Department for Biology and Pathology of Fish and Bees at the Faculty of Veterinary Medicine, University of Zagreb. The fish were caught at the Korana River and were obtained from 3 different fish farms over a 5-year period (2017-2022). All fish collected for this study had grossly visible lesions on different body areas and were examined in collaboration with the Department of Chemical, Biological, Pharmaceutical and Environmental Sciences of the University of Messina. Lesions were analysed by histopathology, histochemistry and immunohistochemistry. Radiology and computed tomography (CT) were occasionally performed as additional diagnostic tests. Macroscopic, histological, histochemical, immunohistochemical, radiological and CT findings in collected fish were consistent with a diagnosis of adenocarcinoma, neuroepithelioma, chondroma, squamous cell carcinoma, fibrosarcoma and fibromatosis. There are very few documented reports of fish tumours in Croatia (Gjurčević et al. 2014), however, here we report the presence of different tumours in both wild and farmed fish. Such reports are particularly useful as fish neoplasms may serve as indicators for the presence of environmental carcinogens (Grizzle & Goodwin, 2010).