The goal of this study was to identify and assess common endo-parasites on Tilapia zillii in the Tono Reservoir, as well as to investigate the mean intensity and prevalence of these parasites. 175 specimens were examined during the study. Endo-parasites of three metazoans and one protozoan were observed from the Tilapia zillii gills, intestines, and stomach. The findings show that the most common endo-parasites affecting Tilapia zillii are Ichthyopthirius multifiliis, Bothriocephalus sp., Contracaecum sp., and Dactylogyrus sp. Contracaecum sp had the highest prevalence of 29.71, followed by Bothriocephalus sp (18.86), Ichthyopthirius multifiliis (12), and Dactylogyrus sp (6.86). The average intensity of Bothriocephalus sp was 0.84, Contracaecum sp was 1.33, Dactylogyrus sp was 0.31, and Ichthyopthirius multifiliis was 0.54. The reservoir's physicochemical parameters changed every month. Low levels of these parameters were discovered to influence the prevalence and distribution of these parasites. Haematological parameters showed significant changes between the two groups. Health status was observed to be improved in the adult group. It was also observed that fingerlings (0.1 g – 20 g) were more infected with significantly lower levels of blood profile. To investigate the presence of these parasites as well as the biotic factors that expose these species to endo-parasites, a long-term study of Tilapia zillii and other tilapia species in the Tono Reservoir should be conducted.