Helminth parasites are among the major pathogens affecting freshwater fishes and may produce severe pathological and metabolic disturbances. The present study investigated histopathological alterations and biochemical changes in helminth-infected freshwater fishes collected from Kelzar Dam, Maharashtra, India. A total of 468 fishes belonging to eight species were examined during June 2021 to May 2025. Histopathological examination of intestine and liver tissues was carried out using standard Haematoxylin and Eosin staining methods. Biochemical estimation of protein, lipid and glycogen was performed using standard laboratory methods. Infected fishes showed villi erosion, haemorrhage, inflammatory infiltration, vacuolization and granultoma formation. Severe tissue damage was mainly associated with Pallisentis ophiocephali and Camallanus sp. infections. Significant reduction in protein (20.1%), lipid (23.1%) and glycogen (27.7%) was observed in infected fishes compared to non-infected controls (p < 0.05). Carnivorous fishes showed greater biochemical depletion than herbivorous and omnivorous species. Increased parasite burden was positively associated with metabolic reduction. Such pathological and metabolic disturbances may reduce fish growth, market quality and reservoir fishery productivity. The findings indicate that helminth infection significantly affects fish health and reservoir fishery productivity.