Occurrence, Morpho-Histopathological Characterization, and Infection Dynamics of Posthodiplostomum sp. (Strigeidida: Diplostomidae) in Cyprinid Fish of the Ganga River

Abstract

A metacercarial infection of Posthodiplostomum sp. (Strigeidida: Diplostomidae) was reported in the cyprinid fish, Labeo catla and Pethia conchonius and was identified based on clinical signs, cyst morphometry and characteristic histopathological lesions. The parasite was oval-round in shape, encysted in musculocutaneous tissues, and well encapsulated. The cyst was 1.02±0.02 by 0.79±0.02 mm and 1.02±0.02 by 0.75±0.02 mm in L. catla and P. conchonius, respectively. Microscopically, the multifocal hyperpigmented areas in the musculocutaneous tissues showed pericystic melanization, focal necrosis, and an infiltration of mononuclear leukocytes. Out of the 5,820 freshwater fish examined, only 3 L. catla were found to be infected in October at the Balagarh and in August, 13 P. conchonius were found to be infected at the Farakka stretch of the Ganga River. The spatio-temporal prevalence of Posthodiplostomum sp. in L. catla and P. conchonius was <1%, indicating a lower infection rate. This is the first report of Posthodiplostomum sp. infection in P. conchonius and from the Ganga River. It is also the first report of Posthodiplostomum sp. infection in L. catla in the Ganga River