Malignant melanoma in an African penguin (Spheniscus demersus): a case report

This report describes malignant melanoma in a 21-year-old African penguin (Spheniscus demersus) maintained under captive management. The penguin exhibited a rapid decline in clinical condition, characterized by lethargy and anorexia, and despite 5 days of supportive fluid therapy, the animal subsequently died. At necropsy, the spleen was markedly enlarged, and multiple black nodules were present in the liver, lungs, kidneys, musculature, ribs, and scapula. Impression smear cytology demonstrated intracytoplasmic dark pigment, and histopathology revealed densely packed, highly invasive melanocytic cells with frequent lymphovascular emboli. Immunohistochemistry showed strong melanoma associated antigen (PNL2) positivity and Melan A negativity, consistent with previously reported penguin melanomas. Age appeared to be the most plausible predisposing factor, whereas a definitive environmental or genetic cause could not be established. Although molting involves dynamic melanocyte activity and physiological stress, there is no direct evidence that it initiates malignant transformation; however, molting-associated changes may mask early disease.