Abstract
Cutured carangid, Seriola purpurascens, infected with sanguinicolid trematodes, Paradeontacylix spp. were examined histopathologically. Fish were sampled bimonthly in Shikoku from March 1984, when mortalities of heavily infected fish occurred, until January 1985. Pathological changes related to the blood fluke infection were limited in the heart and gills. They were summerized as hyperplasia of gills, encapsulation of eggs in the gills and ventricle, and papillate proliferation of the endothelium in the afferent branchial arteries. No necrosis was found in any organs at any stages of infection. The infection had seasonality, and the host reaction changed with it. Survived fish (1+) got milder infection next year than 0+ fish. It is probable from the histological changes in the heart and gills that the cause of mass mortalities among 0+ fish from December 1983 to March 1984 was physical blockage of the blood flow due to accumulation of the eggs in the gill filaments and to papillae formation in the afferent branchial arteries.
