Abstract
An adult female striped burrfish from a public display aquarium, mixed species recirculating system presented for an exophytic yellow–orange mass on the dorsal head suggestive of neoplasia. The mass was surgically excised twice, adding cryosurgical ablation during the second procedure, but recurred both times post‐operatively. After approximately 9 months, euthanasia was elected due to lesion progression. Histopathologic evaluation of surgical biopsy samples and tissues collected at necropsy suggested chromatophoromas. Immunohistochemistry using SOX10, Melan‐A and PNL‐2 antibodies produced no labelling of tumour cells. Ultrastructurally, neoplastic cells contained poorly formed pterinosomes and vesicles consistent with either xanthophoroma, erythrophoroma or a mixed xanthoerythrophroma. Pigment analysis using absorbance spectrophotometry and gas chromatography mass spectrophotometry identified the primary pigment as xanthopterin with low amounts of the carotenoid tunaxanthin, confirming the diagnosis of xanthophoroma, a rare subtype of chromatophoroma in fish.