Abstract
A captive-born, female 13 year-old Orange-spot freshwater stingray (Potamotrygon motoro) presented with an acute bilateral, caudo-dorsal swelling measuring approximately 25x9x18 cm, resulting in elevation of the associated lumbar region. Ultrasonography of this swelling revealed an irregularly organized intra-coelomic mass of varying echogenicity containing fluid pockets. The ray was euthanized and gross necropsy confirmed the presence of a highly irregular, fluid-filled coelomic mass in the region of the reproductive tract composed of multiple tissue types with subsequent compression of adjacent coelomic structures. Histopathology identified the mass as a malignant round cell tumor of the ovary and possibly oviduct. The tumor consisted of sheets of neoplastic cells with anisokaryosis and frequent mitoses. The final diagnosis was a presumptive dysgerminoma.
Neoplastic lesions are rarely reported in elasmobranchs.2,3 Reported neoplasms have included myxosarcoma in spotted ratfish (Hydrolagus colliei), cutaneous fibrosarcoma in a blacktip shark (Carcharhinus limbatus), hepatocellular carcinoma and cholangiocarcinoma, gingival epulis, gastric polyp, and testicular mesothelioma in blue sharks (Prionace glauca), renal carcinoma and thyroid carcinoma in spiny dogfish (Squalus acanthias), and cutaneous melanomas in skates (Order Rajiformes).1-3,5 The vast majority of reported tumors came from wild-caught specimens, with very few cases from public aquaria.5 Other documented findings have included a species predisposition to papillomatosis in bamboo and sand tiger sharks, and cutaneous melanoma in a captive nurse shark (Ginglymostoma cirratum).3,4,6
To the author's knowledge, this is the first known reported case of neoplasia of the reproductive tract in a ray (order Myliobatiformes).
Acknowledgements
The authors would like to thank the veterinary and aquarium staff at the Toledo Zoo for their assistance in this case, as well as the staff at Northwest ZooPath for support with histopathology review.
References
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