Calretinin and S-100 expression in goldfish, Carassius auratus (L.), schwannoma.

Twelve goldfishes, with multiple external tumours, were sent to the laboratory for examination. Tumours appeared as subcutaneous soft, smooth, nodular bulges, with a pale to fairly pink, homogenous cut surface. In HE stained sections, tumours had well defined borders and were encapsulated; composed of elongated cells, with ellipsoid, hyperchromatic nuclei and pale cytoplasm. In the context of the neoplastic proliferation, these cells were usually densely packed and arranged in parallel ranks with distinctive palisading of nuclei, resembling Antoni type A tissue. Intercellular fibres forming interwoven bundles or whorls, and the so-called Verocay bodies, were also detected in some areas of the tumour. Other tumour areas were loosely packed with spindle cells enclosed in a myxomatous stroma compatible with Antoni type B tissue. Immunohistochemistry showed strong positivity in neoplastic cells when tested with S 100 and calretinin. The significance of the study is the statement of goldfish as experimental model for some neoplastic disorders of higher vertebrates. This diagnosis is also supported by positive staining of tumour cells with the calretinin, a specific marker used to distinguish schwannoma from neurofibroma in PNST in humans and here reported for the first time in fish.