DISEASES OF FLOUNDER PLATICHTHYS-FLESUS IN DUTCH COASTAL AND ESTUARINE WATERS, WITH PARTICULAR REFERENCE TO ENVIRONMENTAL-STRESS FACTORS .2. LIVER HISTOPATHOLOGY

This paper reports the detailed histopathological analysis of livers o f flounder Platichthys flesus sampled in Dutch coastal and estuarine w aters during 1985-89. In conjunction with an epizootiological study of grossly identifiable diseases st 10 sampling locations, a total of 21 0 livers (1 % of sampled population) showing gross nodular lesions (di ameter >2 mm) and 315 livers showing no gross pathology were collected . Of the 210 livers with grossly observable nodules, 67 % were diagnos ed as having neoplasms. The majority of these neoplasms were identifie d as hepatocellular adenoma; 13.1 % were diagnosed as hepatocellular c arcinoma. Most of the remaining nodules were diagnosed as foci of cell ular alteration, which are considered to be preneoplastic lesions. Rou tine histopathological examination of livers showing no gross patholog y resulted in the identification of a range of lesions including hepat ocellular adenoma, foci of cellular alteration, hydropic vacuolization of biliary epithelial cells and hepatocytes, inflammatory lesions, fo cal 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 m elanomacrophage centres. The results indicate that a small proportion of neoplasms would be missed if only livers with grossly detectable no dules were subjected to histological examination. The prevalence of fo ci of cellular alteration at the different sampling sites showed a goo d correspondence with that of neoplasms, providing support for the hyp othesis that these conditions represent stages of the same process. Of the other lesions and quantitative indices, only hydropic vacuolizati on of biliary epithelial cells had a spatial distribution similar to t hat 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 a re explicitly taken into account. Furthermore, experimental studies ar e 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 of other environmental and host-related f actors.