Diversity and abundance of zooplankton in the Omo Gibe III Reservoir, Southern Ethiopia

The number of reservoirs in Ethiopia is increasing, primarily for hydroelectric power generation, irrigation, and drinking water supply. However, studies focusing on the aquatic life within the reservoirs are scarce and significantly lagging behind the increasing development of these freshwater ecosystems. The community structure, species composition and abundance of zooplankton in relation to physico-chemical changes were investigated in the Omo Gibe III reservoir in 2024. Zooplankton samples were collected using plankton nets and preserved in a solution containing 5% formalin and Lugol's iodine. Measured physicochemical parameters included a temperature range of 24.30 °C to 31.90 °C, as well as a dissolved oxygen range of 5.4 mg/L to 5.8 mg/L, both of which fall within the optimal range for most zooplankton species. A total of 20 zooplankton species were identified and categorized Rotifera (11 species), Copepoda (5 species), and Cladocera (4 species). The community structure was predominantly represented by Rotifera which accounted for 46.2%, Copepoda for 29.3%, and Cladocera for 24.5%. This study provided valuable insights into the zooplankton community structure of the Omo Gibe III Reservoir, demonstrating how alterations in physicochemical variables can impact species diversity and abundance.