Diseases of flounder Platichthys flesus in Dutch coastal and estuarine waters, with particular reference to environmental stress factors. II. Liver histopathology

Abstract

This paper reports the detailed histopathological analysis of livers of flounder Platichthys flesus sampled in Dutch coastal and estuarine waters during 1985-89. In conjunction with an epizootiological study of grossly identifiable diseases at 10 sampling locations, a total of 210 livers (1% of sampled population) showing gross nodular lesions (diameter > 2 mm) and 315 livers showing no gross pathology were collected. Of the 210 livers with grossly observable nodules, 67% were diagnosed as having neoplasms. The majority of these neoplasms were identified as hepatocellular adenoma; 13.1% were diagnosed as hepatocellular carcinoma. Most of the remaining nodules were diagnosed as loci of cellular alteration, which are considered to be preneoplastic lesions. Routine histopathological examination of livers showing no gross pathology resulted in the identification el a range el lesions including hepatocellular adenoma, loci of cellular alteration, hydropic vacuolization of biliary epithelial cells and hepatocytes, inflammatory lesions, focal necrosis, regenerative foci, and fibrillar hepatocytes of unknown significance. In addition, indices were used to quantify the presence of storage vacuoles (glycogen and lipid) and the relative density of melanomacrophage centres. The results indicate that a small proportion of neoplasms would he missed if only livers with grossly detectable nodules were subjected to histological examination. The prevalence of foci of cellular alteration at the different sampling sites showed a good correspondence with that of neoplasms, providing support for the hypothesis that these conditions represent stages of the same process. Of the other lesions and quantitative indices, only hydropic vacuolization of biliary epithelial cells had a spatial distribution similar to that of neoplasms. It is concluded that liver neoplasms and especially their precursor lesions in flounder are promising tools for monitoring exposure to potential carcinogens, provided that migration patterns are explicitly taken into account. Furthermore, experimental studies are needed to investigate the chemical agents responsible for the onset of these early lesions and their progression into neoplasms, and also to evaluate the contribution el other environmental and host-related factors.