Xanthophoroma in a Striped Burrfish, Chilomycterus schoepfi.

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.