The aim of this study was to investigate the effect of ectoparasites on gills and skin of (Oreochromis niloticus). Fish and water samples were brought to the laboratory from a tilapia fish farm in Riyadh area of Saudi Arabia. A number of (120) fish specimen were equally collected for 1 year on monthly basis. Water samples were examined in the laboratory for physicochemical characteristics (1 L month). Gills and skin tissues were prepared for histopathology and light and scanning electron microscopy. Water characteristics revealed a substantial deterioration of water quality. Mean value ± standard deviation shows low oxygen (2.18 ± 0.082.85 ± 0.14 mg/l), high ammonia-N (2.01 ± 0.452.92 ± 0.66 mg/l), and high nitrite-N. (0.82 ± 0.491.61 ± 0.66 mg/l). Ectoparasites including Trichodina, Monogenea, and Ambiphyra were observed on the infected tissues. Histopathological investigations showed severe gill alterations such as blood congestion, blood hemorrhage, a fusion of secondary lamella, and epithelial lifting. Gill erosion and mucus secretions were also reported on some fishes. The severity of the infection has worsened fish health and lead to death of many individuals. The histopathological changes induced by ectoparasites on fish gills and skin could be used to determine the severity of ectoparasite infection to take measures for better fish farm management and to produce healthy fish for human consumption.
Key words: Oreochromis niloticus, Ectoparasites, Histopathology, Aquaculture, Saudi Arabia.