Abstract
Belugas (Delphinapterus leucas) are Monodontidae cetaceans commonly displayed in aquaria around the world.1 Since 1998 many North American zoological institutions have been involved in a coordinated captive breeding management effort that has resulted in the birth of at least 21 calves.2 The Vancouver Aquarium acquired beluga in 1967 and have since had 5 calves born. In this case series, post mortem findings of 3 juvenile belugas that were not completely weaned and were eating varying amounts of fish are provided. Initial clinical presentation of each case was slightly different, though each calf exhibited inappetance and infrequent nursing for several days, prior to an unexpected and acute death. All three calves were anemic (RBC = 2390/µL) and had mild to moderate inflammatory leukograms, characterized by a neutrophilia (5663/µL) with slight toxic change and occasional Dohle bodies, lymphocytosis (4255/µL), and a moderate monocytosis (524/µL). Gross and microscopic similarities in these cases included massive pulmonary edema and varying degrees of pneumonia, multifocal skeletal myocellular degeneration with scattered dystrophic mineralization, putative cardiomyopathy and myocarditis with peripheral vascular medial vacuolation and occasional necrosis, multisystemic hemosiderosis, low-grade hepatitis and generalized lymphadenopathy with varying degrees of gastritis and enteritis. All three calves tested positive for unspecified Mollicutes and other laboratory analyses to screen for infectious agents proved negative. Heavy metals (including Se) and Vitamin A levels were determined for liver tissue from all three calves and all values were within acceptable reference ranges. The lack of consistent or distinct infectious agents in combination with the histopathological findings in these three beluga cases suggested exposure to a cardiotoxin and led to an investigation of toxins to which the beluga may have been exposed. The Vancouver Aquarium is located adjacent to a large public park with numerous native and non-native plant species that may be introduced into the outdoor habitats. The fact that no calves were observed ingesting plant material is compounded by the difficulty of post-mortemdetection of toxic plant-alkaloids, which is often hampered due to rapid metabolism and degradation of the toxin in question6 and may preclude a definitive diagnosis of toxin exposure. This case series highlights the difficulties encountered in interpreting retrospective data in an attempt to diagnose suspected toxicities in exhibit animals maintained in outdoor habitats.
Acknowledgements
The authors wish to thank Ms. Gwyneth Nordstrom and Chelsea De Colle of the Vancouver Aquarium. The authors thank the Vancouver Aquarium and the Animal Health Centre for technical assistance. Dr. Douglas Justice, Associate Director, Curator of Collections, and Research scientist at the University of British Columbia Botanical Garden and Centre for Plant Research, provided plant identification.
References
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