The composition of fish communities of four Tekeze sub-basin rivers of Tigray, Northern Ethipia

Abstract

Freshwater fish communities are structured by a combination of abiotic and biotic factors, with habitat heterogeneity playing a key role in shaping their composition, distribution, and assemblage structure. This study aimed to investigate the fish community composition and the environmental factors influencing them in four rivers of the Tekeze sub-basin in Tigray, Northern Ethiopia: Atsela, Mesgi, Geba, and Worie. Water quality parameters were measured using standard probes, and fish sampling was conducted using electrofishing across two seasons (December 2019 and April 2020). A total of 2,917 fish belonging to 14 species, four families, and three orders were recorded. Cyprinidae was the dominant family, accounting for 79% of the species. Only two species, Garra blanfordii and Garra dembecha, were common to all rivers. Chelaethiops bibie and Chiloglanis niloticus were uniquely recorded from Worie and Geba rivers, respectively. Labeobarbus intermedius was the most abundant species in Worie and Geba, while Garra species dominated in all rivers. Water quality parameters varied across rivers, with higher temperatures, conductivity, and turbidity observed in lowland rivers (Geba and Worie) compared to highland rivers (Atsela and Mesgi). Fish species richness and diversity were higher in lowland rivers, with Worie recording the highest richness (11 species) and Mesgi the lowest (2 species). Multivariate analysis (CCA) indicated that altitude, temperature, turbidity, salinity, and chlorophyll-a were key environmental drivers influencing fish community structure. The study highlights the importance of altitude and associated environmental gradients in shaping fish assemblages in the Tekeze sub-basin. The findings underscore the need for sustainable management of riverine habitats, particularly in light of anthropogenic pressures such as water abstraction, sand mining, and riparian degradation. Conservation efforts should focus on maintaining habitat integrity and ecological connectivity to preserve fish diversity and support local fisheries.