Fish Community Assemblages Response to Physico-Chemical Variables in River Riana, Kisii, Kenya

Abstract

Rivers support freshwater biodiversity but are increasingly affected by changes in water quality arising from surrounding land-use activities. River Riana flows through agricultural, urban, industrial and forested areas, yet information on how its physico-chemical conditions relate to fish community structure remains limited. This study examined the influence of physico-chemical variables on fish diversity, distribution and abundance in River Riana, a tropical riverine ecosystem within the Lake Victoria Basin, Kenya. Five sampling stations representing different land-use types were selected according to accessibility and habitat characteristics. Triplicate water and fish samples were collected monthly from pools, riffles and runs from September 2022 to August 2023. Temperature, dissolved oxygen, conductivity, pH and total dissolved solids were measured in situ using a multi-parameter YSI meter. Fish were sampled using electrofishing and scoop nets and identified to species level using established taxonomic keys and FishBase. Two-way analysis of variance tested variation in physico-chemical variables, while the Kruskal-Wallis test assessed differences in fish abundance. Fish diversity was evaluated using Shannon-Wiener and Pielou’s evenness indices, and Pearson correlation analysis examined relationships between water quality variables and fish abundance. Physico-chemical variables varied across the study sites, with temperature ranging from 19.1–23.7°C, dissolved oxygen from 1.67–4.60 mg/L, pH from 3.11–7.78, conductivity from 60.3–341 µS/cm, and total dissolved solids from 43.2–224.69 mg/L. A total of 2,715 fish belonging to 5 families and 16 taxa were recorded. Fish abundance was highest at Station 5 (1,025) and lowest at Station 1 (74). Shannon-Wiener diversity ranged from 0.000 to 0.452, while Pielou’s evenness ranged from 0.000 to 0.176. The results indicate that physico-chemical conditions influence fish assemblages in River Riana and support the need for continued water quality monitoring and riparian management.