Abundance, distribution, and diversity of fishes in Ribb Reservoir, Lake Tana basin, Ethiopia

Abstract

The abundance, distribution, and diversity of fishes in Ribb Reservoir were studied based on a total of 1629 fish samples collected from February to October 2021. Fish samples were collected using gillnets of different stretched mesh sizes. Except for temperature and pH, most physico-chemical variables revealed significant spatial variation (ANOVA, p < 0.05). Fishes were highly correlated with the concentration of dissolved oxygen (r ≈ 0.8, p < 0.01) and electrical conductivity (r ≈ 0.89, p < 0.01). Three fish species include Oreochromis niloticus (Linnaeus, 1758), Clarias gariepinus (Burchell, 1822) and Labeobarbus intermedius (Rüppell, 1835) were identified (H' = 1.06). The diversity indices did not show variations among seasons (H' = 0.98–0.907) and sites (H' = 1.04–1.07). All the fish species occurred in all sampling sites and seasons. Oreochromis niloticus (41.9%) was the most important and abundant fish species followed by C. gariepinus (38.2% by %IRI). The relative importance index showed O. niloticus (45.4%) was the most abundant species in the dry season. However, C. gariepinus (73.3%) was the most abundant species in the wet season. Before the construction of the Ribb Dam, the Ribb River was dominated by about eight species. However, in the current study (after the construction of the Ribb Dam), only three species were found. Results revealed that the diversity of fishes has decreased primarily due to the dam effect followed by anthropogenic impacts such as poor land management systems, high sedimentation load, excessive irrigation and illegal fishing. Therefore, an appropriate dam design with a fish ladder and effective watershed management setup is needed to sustain fish resource utilization in the country for food security.