Evaluating Fish Community Structure In Relation To Water Quality Along Nyangweta Tributary, Kuja- Migori River Basin, Kenya

Abstract

Riverine ecosystems support diverse fish communities and other aquatic organisms. However, studies on fish community structure and their condition in relation to water quality changes are few and limited to large and navigable rivers that support commercial fisheries. To address this gap, a six-month study was conducted in the Nyangweta tributary of the River Kuja-Migori basin from October 2020 to March 2021. The objective was to investigate the changes in fish community structure in response to spatio-temporal variations in water quality parameters. Physico-chemical parameters such as temperature, dissolved oxygen (DO), electrical conductivity (EC), total dissolved solids (TDS), pH and turbidity were recorded in situ using the YSI multi-parameter meter, while total nitrogen (TN) and total phosphorus (TP) were analyzed using standard methods. Fish samples were collected using an electro-fisher and the total length and body weight measurements recorded and used to determine Fulton's (KF) and allometric (Ka) condition factors. Two-way ANOVA was used to test whether there were any significant differences in physico- chemical variables and fish abundance in each station and Tukey’s Post hoc test was performed to determine the source of mean differences. The Nyangweta tributary fish communities were characterized using habitat quality, diversity and evenness indices and presented as mean (±SE) Similarly, the temporal mean temperature was significantly different among the sampling months. The mean pH values showed a general decreasing trend from October to March, while EC, temperature and TDS increased during this period. The spatial mean DO level was significantly different (p = 0.02) among the sampling stations. Comparatively, upstream stations recorded lower mean DO concentrations than downstream stations. The Nyangweta tributary fish communities comprised of 696 fish from 6 families and 13 species. The dominant fish species belonged to the Cyprinidae family, with Labeobarbus altianalis comprising 36.49% and Clarias theodorae comprising 30.17% of the riverine fisheries respectfully. The largest species was Enteromius altianalis (70.74 ± 8.72 g), followed by L. altianalis and Labeo victorianus with mean body weights of 62.14 ± 3.48 g and 56.43 ± 11.26 g respectively. Fulton's condition factors (KF) were greater than 1 for all species except E. altianalis and C. theodorae but not significantly different (p = 0.43) among the species. Length-weight relationships were significant (p < 0.05, R2 > 0.5) and yielded a positive allometric (Ka > 3) growth for four species, while isometric growth (Ka = 3) was observed for L. altianalis. A general increase in fish diversity was observed downstream. Water quality parameters influenced the fish abundance and diversity in the stream. Variations in physico-chemical parameters were attributed to seasonality changes and anthropogenic activities. A high downstream abundance of L. altianalis and L. victorianus during the rainy season is due to migration of gravid fishes of migratory potamodromous fish into the stream to spawn. Regular monitoring of water quality parameters along the Nyangweta tributary is required to track changes over time to provide timely intervention, enforcement actions, and appropriate conservation and management measures to protect and restore the health of riverine ecosystems. The findings suggest that conservation measures should be implemented to improve water quality and the abundance, diversity, distribution and condition factor of fish in the upstream areas of the Nyangweta tributary.