Visceral neoplasia and epidermal papillomas in cultured turbot Scophthalmus maximus

Abstract

Skin papillomas, mainly composed of epidermal hyperplasia and visceral tulnors involving the pancreatic and occasionally the blle ducts, were observed in a population of juvenile turbot Scophthalmus maximus reared in a fishfarm located in the northwest of Spain. By electron microscopy, the epidermal hyperplastic tissue had Malpighian cells with irregular nuclei and abundant glycogen-like particles and free ribosomes in the cytoplasm. In visceral tumors, proliferation of the pancreatic ductular epithelia1 cells was acconlpanied by growth of surrounding smooth muscle cells and connective tissue. Pancreatic acinar cells were vacuolated. Some affected fish also presented lesions in the liver, spleen and kidney. Attempts to isolate virus using different fish cell-lines were negatlve Similarly, no viral particles were observed by electron microscopy. However, bacteriological analysis revealed the presence of the Vibrio fischeri-V harveyi group in the internal organs of the majority of affected fish. which supports a possible contribution of these bacteria in the development of mortality. High pressure liquid chromatography analysis has not detected the presence of allatoxin B, in tissues. At present the origin of these tumors in turbot remains unclear INTRODUCTION