Histology of selected organs of Clarias gariepinus infected with the metacercaria of a digenean trematode

Abstract

Fish have become a major source of protein and essential fatty acid for fish lovers in the world. Thus, many farmers are venturing into fish farming but have challenges due to fish diseases and parasites. This study examined the possible pathological lesions associated with digenean trematode infections in the Clarias gariepinus. Clarias gariepinus juveniles reared in fibre-glass tanks under intensive, flow through system were obtained from a commercial farm. Aquatic snails were obtained from earthen ponds on three commercial fish farms. The presence of cercaria was established in these snails, which were reared in laboratory conditions with Clarias gariepinus juveniles, for two weeks, to cause infection. Age matched un-infected Clarias gariepinus served as controls. Presence or absence of metacercaria after histological examination was used to determine infected and controls, respectively. Fish were sacrificed after two weeks and organs reexamined for the presence and absence of metacercaria. Preliminary examination using wet mount revealed the presence of metacercaria only in the gills of juveniles reared with infected snails. Histological staining and examination using haematoxylin and eosin stain, revealed histopathological lesions in the gills, kidneys, liver, spleen, brain and skin. Lesions included loss of secondary filaments in the gills, tubular degeneration and necrosis in the kidneys, vacuolations and spongiosis in the cerebellum and liver, and loss of pigmentation in the skin. There were no lesions observable in the intestine and stomach. Findings obtained from this experiment indicate that the presence of parasites in the gills alone is cause for concern, especially in commercial fish farming. It is postulated that the lesions in other organs may be partly due to the disruptive effect on the gills resulting in oxygen deprivation. In conclusion, there was significant disruption of these organs due to massive invasiveness of metacercaria in the gills, which may lead to economic losses and possible zoonosis. Measures targeted at snail control in earthen ponds with fiches, will break the transmission chain, and prevent digenea infestation in cultured fish.