Putative Rodlet Cell Neoplasms in the Livers of Two White Suckers (Catostomus commersonii)

Although discovered more than a century ago, piscine rodlet cells (RCs) remain somewhat of a mystery to scientists in terms of their origin and function. Initially described as parasites, and later as potential secretory cells, the prevailing theory is that RCs are leucocyte-like cells that possess pathogen defence capabilities. The current case report involves a novel type of neoplasm discovered in the livers of two adult female white suckers (Catostomus commersonii) that were collected as part of a survey of fish from the St. Mary's River Area of Concern, in which sediment contaminated by polyaromatic hydrocarbons has been associated historically with a high prevalence of liver neoplasms in white suckers. The two tumours in this study were investigated by light microscopy, histochemical staining, immunohistochemical labelling for S100 protein and transmission electron microscopy. The evidence from these investigations suggests that these neoplasms may be derived from de-differentiated RCs or RC precursors. The unanticipated existence of these solid mesenchymal-like tumours may prompt a reassessment of the current dogma regarding the physiological function of RCs.