Fish Biodiversity as a Biological Indicator of Aquatic Environmental Quality in Wetlands of Lake Tana, Ethiopia

Abstract

Fish biodiversity was assessed as a biological indicator of aquatic environmental quality across six wetlands of Lake Tana, Ethiopia. A total of 1616 fish specimens, representing 18 species, four genera and three families, were collected. Labeobarbus intermedius (23.1%–48.9%) and L. brevicephalus (6.7%–44.4%) were the most abundant, whereas L. beso, L. gorguari and L. truttiformis were least common (0%–6.7%). Spatially, Clarias gariepinus dominated at Megech River Mouth (9.4%), and Oreochromis niloticus was abundant at Wonjeta (54.5%) and Ras Abbay (62.5%). Catch Per Unit Effort (CPUE) ranged from below the detection limit to 110.0 fish/h. The Fish Index of Biotic Integrity (FIBI) and Habitat Quality Index (HQI) varied significantly, with the highest FIBI values at Gumara and Megech River Mouths (39.0) and HQI scores peaking at Zewdie Girar (19.0) and Wonjeta (18.5). Multivariate analyses grouped wetlands into three distinct clusters based on the fish assemblage structure: Cluster 1 (Wonjeta, Ras Abbay and Avaj), Cluster 2 (Zewdie Girar and Gumara River Mouth) and Cluster 3 (Megech River Mouth). Principal Component Analysis explained 80.6% of the total variation, whereas Canonical Correspondence Analysis accounted for 98.5% of the variance in fish–environment relationships, identifying water depth, Secchi depth, ammonia, phosphorus and nitrate as key drivers of environmental degradation. Margalef's richness and Hill's diversity indices varied significantly among wetlands, reflecting spatial differences, but showed no significant seasonal variation. Functional feeding group distribution exhibited seasonal shifts, especially among benthic, tolerant and detritivorous species. These findings underscore the ecological importance of Lake Tana's wetlands and the need for targeted conservation measures to sustain fish diversity and habitat integrity.