Mohaddes Ghasemi - Inland Waters Aquaculture Research Center, Iranian Fisheries Science Research Institute (IFSRI), Agriculture Research Education and Extension Organization (AREEO), Bandar-e Anzali, Iran.
Issa Sharifpour - Iranian Fisheries Sciences Research Institute (IFSRI), Agricultural Research, Education and Extension Organization, Tehran, Iran.
Somayeh Haghighi Karsidani - Department of Fishery, Faculty of Natural Resources, Bandar Anzali Branch, Islamic Azad University, Bandar-e Anzali, Iran.
Zahra Eynizadeh - Department of Animal Sciences and Marine Biology, Faculty of Life Sciences and Biotechnology, Shahid Beheshti University, Tehran, Iran.
Hasti Azarabad - Department of Pathology, Hamidreza Fattahian Pet Hospital, Tehran, Iran.

Background: Due to the multifactorial etiology, tumor manifestation in any vertebrate species may become a critical issue. This topic requires more consideration for species in aquatic ecosystems as an enclosed habitat. In addition, knowledge about oncogenesis in the aquaculture industry enhances the quality of products and its earned benefits.Objectives: This study investigated the tumor lesions, their characteristics, and probable causes, in the most commercially important fish in the southern Caspian Sea: Caspian white fish (Rutilus kutum). Methods: To accomplish this goal, after gross pathology of more than ۲۰ cases, histopathological examinations and electron microscopic assays were employed.  Results: The findings confirmed squamous cell carcinoma and squamous cell papilloma in the examined cases. Furthermore, the virus-like particles were clearly observed in the transmission electron microscopy results, indicating the probable viral etiology for these neoplastic lesions in Caspian Kutum. Conclusion: This study is the first to report the tumor prevalence in fish species of the southern Caspian Sea, which could be an alert for the mentioned ecosystem’s health and the whole aquaculture industry.

Caspian Sea, Fish Neoplasm, Squamous cell carcinoma, Squamous cell papilloma, Tumor viruses