Abstract:
The aquatic biodiversity performs several critical roles in ecosystem functioning through their numerical abundance, taxonomic diversity, and trophic significance. This study aimed to evaluate the impacts of Rusumo Waterfall on fish communities of Akagera River by assessing the spatial distribution of fish species in two biotopes: upstream and downstream from Rusumo Waterfall, Akagera River, Kirehe District, Rwanda. Primary data were collected at four fishing stations using the stationary-point-count technique, and fish were identified directly on the field and in the laboratory using morphological analysis. The secondary data for fish of Rwanda was obtained from Rwanda Biodiversity Information Systystem (RBIS,2024). The results showed that a total of 1836 fish individuals from 14 species richness belonging to 9 families were recorded from 4 fishing stations. Four fishing stations were strictly selected, two at each biotope from Rusumo waterfall. The results showed that from all recorded fish individuals, they were dominated by Oreochromis niloticus with 680 species abundance represented by 37.04%, followed by pollimyrus nigricans with 540 species abundance representing 29.41% of all sampled fish individuals. Results also showed that species richness is higher at downstream with 14 species compared to upstream with 5 species . The downstream also has higher fish diversity with Shannon Wiener Index (H) of 1.5 compared to the upstream represented by H of 0.3, and also the species from downstream are higher evenness distributed with evenness (J) of 0.6 than upstream with 0.2. Among fifteen identified fish species, four are threatened as listed on the IUCN Redlist. Those are Labeo victorianus (Critically endangered), Haplochromis erythromaculatus (Endangered), and Cyprinus carpio (Vulnerable), and Synodontis ruandae (Vulnerable) which also recently recorded in other hydrological network in Rwanda, beyond Akagera River. This research confirms that there are impacts of Rusumo Waterfall acting as a natural bio-geographic barrier for fish dispersal and preventing species exchange among regions as demonstrated by (Torrente-Vilara et al., 2011). Further studies are needed to assess the impacts of local environmental conditions, and physico-chemical variables on the composition and structure of fish assemblages in the interface of waterfall. Finally, the researcher calls the catchment conservation and management planners to take into account the sustainable management of freshwater hydrological networks, by considering the waterfall as a natural barrier for fish distribution
