Abstract
An adult yellowbar angelfish (Pomacanthus maculosus) presented with a solid brown mass with an irregular surface that extended beyond the gill arches and displaced both opercula. The fish was anesthetized with MS-222 and a 4 cm x 3 cm x 3 cm mass was incompletely excised. The fish recovered well from the procedure and was clinically normal for a week. Subsequently, it developed anorexia and was euthanized twelve days later. Necropsy revealed a remaining mass measuring 3.5 cm x 2 cm x 2 cm that extended ventromedially from the gill arches. Thyroid tissue extended from the primary mass to the heart base, but did not invade the cardiac tissue. Histopathologic examination revealed a moderately cellular, non-encapsulated, infiltrative mass composed of thyroid follicular epithelium in various stages of activity generally forming follicles but often exhibiting disorganized patches. Moderate anisocytosis and anisokaryosis were noted but mitoses were rare. These findings were consistent with a diagnosis of thyroid carcinoma.1 Blood was collected pre-mortem on the affected fish, as well as two control fish of the same genus. Analysis of serum thyroid hormones revealed T4 levels below detectable limits for all three fish. The active hormone in fish, T3, was lower in the affected fish than in the controls. Thyroid hormones play a role in growth and development of fish, and the difference in circulating T3 levels may be due to differences in stages of growth or reproduction.2,3 Thyroid tumors have been documented in a number of teleost species; associations with the hormone levels related to these conditions better defines neoplastic versus hyperplastic changes.
Acknowledgements
The authors would like to thank Erika Nilson for her assistance with necropsy and tissue preparation.
* Presenting author
+ Student presenter
Literature Cited
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