Keywords:River Nile, Rosetta Branch, water quality, heavy metals, Orechromus niloticus, Inter-simple sequence repeats (ISSR)The present study aims to evaluate the water quality of two locations in Rosetta Branch of River Nile and its histopathological and genetic adverse effects on Nile tilapia (Oreochromis niloticus). Water and fish samples were collected from up and downstream of El-Rahawy Drain discharge point (location I and II, respectively) during the summer and winter seasons. The water quality, liver histopathology and DNA alteration of fish was examined. ISSR-PCR technique was used to assess the genetic variation of fish samples from these locations. The water quality parameters ( BOD, COD,……)were increased at location II compared with location I in addition to depletion in dissolved oxygen. Moreover, the fish samples collected from location II showed severe histological and molecular alterations than those collected from location I. It is recommended that the government must increase the awareness of people around the River Nile, and improve the environmental management to reduce the risks of polluted water and consuming the fish exposed to this water on human health. Hashem et al. , 2020 20Impact of the water quality of River Nile on Oreochromis niloticus _________________________________________________________________________________ 21

Water pollution is one of the most principal environmental and public health problems in the River Nile. In the present study, aims were directed to evaluate the biochemical, histopathological, and genetic effects of El-Rahawy Drain pollutants on the Nile tilapia (Oreochromis niloticus). Hence, during the summer of 2018 and winter 2019, fish samples were collected from two locations (upstream and downstream) of El-Rahawy drain in the River Nile at the Rosetta Branch. Biochemical studies (Total Protein, Albumin, Globulin, A/G, total lipids, Cholesterol, AST, and ALT) were carried out for the specimens and important results were revealed. Compared with the fish caught from the upstream, a deterioration was detected in the health status of the downstream-fish; displaying more extreme histopathological and molecular variations. Using SSR (simple sequence repeats) to detect the molecular effects of water pollutants on O. niloticus, molecular markers indicated genetic differences in fish samples from the same sex in the different studied locations. Consequently, to prevent disease outbreaks and aquatic ecosystem disturbances, the Rosetta Branch is recommended to have an intensive water-quality monitoring program, and wastewater treatment as well.