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

Freshwater fish communities are structured by complex interactions between abiotic and biotic factors, with habitat heterogeneity playing a key role in shaping species composition and distribution. In the Tekeze sub-basin of Tigray, Ethiopia, little is known about the fish communities inhabiting its rivers, despite their ecological and socioeconomic importance. This study aimed to assess the fish community structure and identify the environmental drivers influencing species composition in four rivers (Atsela, Mesgi, Geba, and Worie) of the region. Fish were sampled using standardized electrofishing protocols across two seasons (cold-dry and hot-dry). Physico-chemical parameters (temperature, dissolved oxygen, pH, conductivity, turbidity, etc.) were measured to characterize water quality and habitat conditions. A total of 2,917 fish belonging to 14 species were recorded. Only two species (Garra blanfordii and Garra dembecha) were common to all rivers, while six species were shared between Worie and Geba. Labeobarbus intermedius dominated in Worie and Geba, whereas Garra spp. was most abundant across all rivers. Water quality varied significantly among rivers, with higher temperatures, conductivity, and turbidity in lower-altitude rivers (Geba and Worie). Altitude and river-specific environmental conditions strongly influenced fish diversity, composition, and assemblage structure, with higher species richness in lower-altitude rivers. Altitude and associated environmental gradients—particularly temperature, conductivity, and turbidity—were key drivers of fish community structure in the Tekeze sub-basin rivers. These findings underscore the importance of river-specific conservation strategies, especially for lower-altitude systems that support higher fish diversity but are also more susceptible to human impacts such as water extraction and sand mining.