Histopathological Studies on Vibriosis of the Japanese Eel (.Anguilla japonica)-I. Natural Infection

Abstract

New vibriosis of the Japanese eel broke out in Tokushima prefecture in 1975. Muroga et al. (1976) reported that the causative bacterium had charactaristics resembling those of V. angillicida (Bruun. 1932). The present authors histopathologically observed this vibriosis. A small red patch in early stages or a swollen lesion exhibiting hemorrhage and cutaneous necrosis in advanced cases was observed in the trunk or tail of the diseased fish. Internal gross symptoms of the advanced cases were congested liver, swollen spleen with dark-red coloration, reddish intestine with epithilial desquamation, softened kidney and vascular dilatation of the viscera. Histopathological observation defined that a main lesion was an infected lesion involved skin and lateral musculature. In the early lesion the bacterium penetrated the dermis, subcutaneous adipose tissue and red musculature and in the advanced cases they spread moreover myoseptum and lateral musculature. The lesion showed necrosis of the affected tissue, extensive vascular dilata tion, serous exudation and hemorrhages. Epithelial slough from the edematous, hemorrhagic dermis was also accompanied in the affected skin. In particular in the advanced cases necrosis, circulatory derangements and bacterial multipoication became more intensive and extensive. The advanced cases underwent systemic infection. Metastatic lesions showing necrosis and circulatory derange ments were observed in the spleen, liver, kidney, heart, gills and intestine which was particularly followed by desquamative catarrh. © 1977, The Japanese Society of Fish Pathology. All rights reserved.