Blood fluke infection of cage reared Atlantic bluefin tuna Thunnus thynnus in west Mediterranean

Abstract

Infection of a blood fluke, possibly Cardicola sp. (Digenea: Aporocotylidae), in reared Atlantic bluefin tuna Thunnus thynnus was investigated. Parasitological analyses included visual examination of the heart for the presence of adult fluke and stereomicroscopic and histopathological analyses of the gill to assess the presence of lesions caused by parasite eggs. No adult flukes were found in the hearts. Some of the gills exhibited small white to yellow foci involving single filaments. Blood fluke eggs were found in gill tissue sections of 29.6% of sampled tuna. A slight inflammatory response was observed around most of these eggs, while occasionally individual eggs were encapsulated by a granulomatous reaction. Despite the absence of remarkable pathological effects in the infected tuna, blood flukes combined with other agents may cause major problem.