Squamous cell carcinoma in a wild European bullhead Cottus gobio.

A pharyngeal tumor was found in a wild European bullhead. The tumor mass appeared underneath the operculum and was bilobed. The major neoplastic component showed diffuse epithelial squamous differentiation. Crossmonn's trichrome allowed identification of connective tissues whereas no neoplastic cells were stained. Periodic acid-Schiff was negative within the mass, and Giemsa did not show any further diagnostic significance. Immunohistochemistry showed diffuse positive cytoplasmic staining of the neoplastic population with an anti-human pancytokeratin antibody. Vimentin was negative and exclusively stained the stroma. On the basis of the morphological and immunohistochemical results, a squamous cell carcinoma was diagnosed.