First Report of Fibromyxoma in a Greater Amberjack (Seriola dumerili) From Aquarium of Genoa.

In teleosts, mesenchymal tumours like fibromas are frequently observed, whereas their malignant counterparts, fibrosarcomas, occur only sporadically. In our study, an adult female greater amberjack (Seriola dumerili) reared at the Aquarium of Genoa developed a slow-growing mass protruding from the ventral right side of the head. The tissue was firm and white greyish with localized cranial haemorrhaging on the external surface. Cut-section examination showed a homogeneous, dry, whitish and richly vascularized tissue layout. Tissue samples from the mass were stained with Masson's Trichrome, Alcian Blue-PAS (pH 2.5), and Toluidine blue for differential diagnosis. Microscopically, it was characterized by alternating collagenous spindle-cell septa and hypocellular metachromatic myxoid areas positive for acidic mucopolysaccharides and glycosaminoglycans. The absence of cellular atypia, mitotic activity and necrosis confirms the diagnosis of fibromyxoma. Documenting rare tumours in aquarium fish expands comparative pathology literature and highlights public aquaria as valuable research platforms for long-term health monitoring under controlled husbandry conditions.