Incidental observations of Atlantic tomcod during routine laboratory processing revealed that a portion of the adult population, collected during the 1977-78 spawning season had enlarged livers containing dark coloured tumours and other abnormalities. Ofthe total of 264 livers collected between 16 January and 27 February 1978 and grossly examined for prevalence of abnormalities, 25% appeared to contain neoplastic nodules and hepatocellular carcinoma. One liver contained a massive tumour (7 x 12 mm) that involved approximately 60% ofthe liver. The exact causes of the high prevalence of hepatocellular carcinoma are unknown but polychlorinated biphenyls (PCBs) are suspected of having a possible role. The Hudson River is known to contain elevated concentrations of PCBs. Twelve tomcod livers from the 1977-78 spawning population representing both normal and hepatoma conditions contained concentrations of PCBs ranging from 10-9 to 98-2 ppm (mean of37-5ppm).

Atlantic tomcod (Microgadus tomcod) collected from the Hudson River estuary during the winter spawning season revealed neoplastic and preneoplastic lesions in livers from 44% of the age 1 individuals and 93% of the age 2 individuals collected. These lesions appear as a continuum ranging from basophilic foci with little cellular alterations to hepatocellular carcinoma frequently involving the entire liver. Lesions were more prevalent in larger individuals within the same age group, suggesting a relationship between growth rate and tumor expression. Atlantic tomcod from a relatively unpolluted estuary in Connecticut did not reveal a comparable prevalence of hepatic lesions. Juvenile tomcod collected from the Hudson during the summer, only 4–5 mo prior to the winter spawning season had no hepatic lesions, suggesting that these lesions form rapidly, coincident with gonadal maturation. Chemical analysis of liver tissue revealed high levels of PCBs (2.5–38.2 mg/kg) and the presence of several pesticides including DDT (and metabolites), chlordane, and dieldrin (<0.1–3.0 mg/kg) and several heavy metals (<0.1–6.5 mg/kg). These results suggest that chemical contamination of the lower estuary nursery areas, coupled with high-temperature stresses of summer, may contribute to the high levels of hepatic lesions observed.

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The livers of Atlantie lomcod, Microgadus tomcod (Walbaum), from the Hudson and Paweatuek Rivers were evaluated histologically and described using paraffin and plastic sections. Fatty infiltration, basophilic foci, areas of cellular alteration and hepatoeellular carcinoma were widespread in Hudson River samples, ln fact, no truly normal tissues were found. Paweatuek samples had variable levels of lipid and a low prevalence of other alterations. Evaluation of the histological evidence suggests that hepatocellular carcinoma in Hudson River tomcod results from multiple DNA lesions and that areas of cellular alteration give rise to the larger, more invasive form of hepatocellular carcinoma. Glutaraldehyde and OsOj fixed livers were used to determine differences in cell types and lipid levels. Paweatuek samples possessed hepatocytes and dark cells forming the parenchymal tissue, whereas Hudson samples lacked dark cells. Hepatic lipid levels were significantly higher in Hudson River fish than in Paweatuek fish, 36 3 and 11 07o respectively. The elevated hepatic lipid levels in Hudson River tomcod may represent a metabolic response to detoxification.