Abstract

A 262.0 cm long and approximately 217 kg, shark-scavenged adult female Risso’s dolphin (Grampus griseus) stranded alive on Hollywood Beach, Florida, USA and subsequently died. Stranding response was conducted, including carcass removal and transport, gross necropsy, histopathology, and ancillary diagnostics. Cause(s) of stranding and subsequent death were not definitively determined in this case. Post-mortem examination revealed a discrete, 4.5×3.8 cm, firm, tan mass associated with the mesentery, composed of polygonal to strap-like cells forming fascicles. There was mild anisocytosis and anisokaryosis, and vascular invasion was observed. Other findings included a herpesvirus and papillomavirus PCR-negative vaginal plaque with mucosal epithelial dysplasia and lymphoplasmacytic vaginitis, pulmonary fibrosis, gastric nematodiasis, pterygoid sinus trematodiasis, and blubber cestodiasis. Uterine horn asymmetry suggested prior pregnancy. A PCR panel for coronavirus, influenza, parainfluenza, morbillivirus, and Mycoplasma spp. in pulmonary tissues was negative. Mass spectrometry of liver samples revealed relatively high concentrations of cadmium (155 µg/g) and mercury (488 µg/g). Rhabdomyomas are benign, primitive, mesenchymal tumors with a tendency for striated muscle tissue differentiation.¹ To our knowledge, rhabdomyomas have only been rarely reported in cetaceans, and this is the first report of this tumor type in a Risso’s dolphin.^2,3

Acknowledgements

The authors thank the Marine Animal Rescue Society (MARS) for providing stranding response and carcass transport to the necropsy lab. We also thank NOAA NMFS for assistance in logistics and coordination. FAU HBOI’s Marine Mammal Stranding and Population Assessment Team assisted with post-mortem examination, including Lydia Moreland and Brooke Davis. This work was funded by the Florida Protect Wild Dolphins and Protect Florida Whales License Plate Funds, which are granted and administered through the Harbor Branch Oceanographic Institute Foundation.

*Presenting author

Literature Cited

1.  Fritchie K. Rhabdomyoma. In: van Krieken J, eds. Encyclopedia of Pathology. Springer, Cham; 2020:1–3.

2.  Newman SJ, Smith SA. Marine mammal neoplasia: a review. Veterinary Pathology. 2006;43(6):865–880.

3.  Gulland FM, Dierauf LA, Whitman KL, eds. CRC Handbook of Marine Mammal Medicine. CRC Press; 2018.