Abstract All diseases manifest as abnormalities in cellular biomolecules, chemical reactions, or processes. Cestode infections, which are common in almost all vertebrates, are mostly caused by obligatory parasites. Once the parasite enters the host organ, it adapts itself and causes some pathological changes, such as mechanical damage or effect of toxic substances, and sometimes decline in growth. Cestode parasites use food from the intestinal gut of the host. Metabolism depends on the feeding habits and rich nourishment available in the gut of the host. In the present study, biochemical components of the cestode parasite Phyllobothrium vatsalabaiae n. sp. and its host Chiloscyllium plagiosum (Anonymous (Bennett), 1830) from the west coast of Raigad District () India, were investigated. The results showed that the examined fish species could have suffered from malnutrition due to cestode infection.