Remarkable papillomas in white sturgeons,Acipenser transmontanus, reared in an aquarium

Papillomatous growths on the ventral surface of the body and paired fins of the white sturgeon,Acipenser transmontanus Richardson, were described histologically with the aid of light and electron microscopy. Contrary to the usual state of intact squamous epithelium being equipped with microridges, no such surface structures were apparent in the papillomatous tissue. The growths appeared to be an aberrant elevations of proliferated dermal tissue, which sustains the hyperplastic Malpighian layer consisting of the stratum spinosum (prickle cell layer) and sbasale. Many intercellular bridges were found, constructed from prominent projections, with distinct demosomes and many tonofilaments. The likely causative agent was mechanical irritation between the small aquarium tank and growing sturgeon, since no viral and/or parasitic inclusion bodies were encountered in the cells.