Histological studies on the effects of Clinostomum marginatum (Digenea, Clinostomidae) in its second intermediate host Loricariichthys platymetopon (Osteichthyes, Loricariidae) of the upper Paraná River, Brazi

Abstract

The histopathology of the infection of Loricariichthys platymetopon (Osteichthyes, Loricariidae) by Clinostomum marginatum (Digenea, Clinostomidae) is described in this study. The parasites were found encysted in the base of the fins, muscle, inner wall of the operculum, lips, gill arches, palate, bone plaques and eyes, forming small white-yellowish nodules. In all the locations the parasites were surrounded by a fibrous capsule consisting of a layer of dense connective tissue followed, in most of the cases, by a layer of loose connective tissue. The thickness of these layers varied with the location of the parasites. In some cases, infiltration by lymphocytes and macrophages within the connective layers was observed. When the parasites encysted under the integument a decrease of the epidermis height and disappearance of the dermis were also observed. The fat tissue near the cysts was invariably destroyed in a greater or lesser extent, and replaced by cell fragments in conjunction with granular material. In some cases this feature could be observed in places a little further away from the cysts and not only in their vicinity. Furthermore, in some cases digitations of destroyed fat tissue extending within the normal tissue were present. When the parasites encysted within the muscle tissue a slight degeneration of the muscle fibers was sometimes observed. In the eyes the parasites were encysted in the sclera, being enveloped by connective tissue, and causing deformity of the eyeball.