Longitudinal fish species diversity and distribution in a medium-sized Afro-tropical river in the Lake Victoria Basin

Abstract

Despite significantly influencing fisheries characteristics of major global basins, medium-sized rivers such as Awach Kibuon remain the least studied. This study evaluated longitudinal fish species diversity, distribution, and environmental influence in Awach Kibuon River, Lake Victoria Basin, Kenya, to inform sustainable management of fisheries resources within the region. Nine sites located in different zones of the river were sampled monthly for eight months in 2019 and 2020. Fish samples were collected for 45 minutes using a backpack electrofisher on a 50-m river reach in every sampling site. Selected physico-chemical parameters (pH, total dissolved solids (TDS), dissolved oxygen (DO), temperature, conductivity, and turbidity) were measured in situ using standard methods. Longitudinal river fish diversity was assessed using species richness, Simpson's Index (D), Shannon-Weiner Index (H′), and Pielou's Evenness Index (J). A total of 983 fish specimens belonging to 21 species, 12 genera, seven families, and six orders were caught during sampling. Cyprinidae was the most dominant family, represented by nine species, followed by Claridae, Mochokidae, and Cichlidae, represented by three species each. Longitudinal species richness, abundance, and diversity indices deviated from the expected downstream increase. Upstream stations had no fish, whereas midstream and river mouth stations had moderate and high species diversity, respectively. Pearson's correlation analyses showed that temperature, conductivity, TDS, depth, and velocity influenced fish species richness in the river. The above findings call for the inclusion of medium-sized rivers in fisheries management plans of Great Lakes Basins for sustainability.

Assessment of the current status of water quality and nutrients enrichment of rivers Kisat and Auji and Nyalenda wastewater sedimentation ponds using multivariate technique

“…This high electrical conductivity may be attributed to an increase in the concentration of salts as a result of degradation of organic matter and also due to high concentration of dissolved solids due to the discharge of high volume of untreated municipal, domestic and hospital wastes into the WWSP. However, the levels of electrical conductivity reported in the present study particularly River Kisat (329.51 -497.83S/cm) were lower than those reported by [18] (435.6 -795.2) and [28] (390.75 -839.65) (Table 2) but higher than what [27] reported in Awach Kibuon River. The results of EC observed in the present study were within the WHO standard limit of 1000 S/cm [37].…”

“…The high TDS recorded could be due to the dissolved salts in the pre-treated wastewater. The levels of TDS obtained in this study were higher than that found by [19,21,27[ in rivers Mara, Vaigai (India) and Awach Kibuon. Similarly, TDS recorded in both River Kisat and Auji was higher compared to those reported in River Gudar (133.00 -179.00), a peri-urban river in Ethiopia [25] This suggests that there is an addition of organic matter and solid wastes into the studied rivers.…”

“…Furthermore, the increased rate of oxygen uptake through the breakdown of organic matter by microorganisms could be the leading cause of DO deficit [8]. In comparison with other rivers, the levels of DO recorded in this study was lower than what [19,27] reported in Mara and Awach Kibuon rivers respectively but comparable to the levels reported by [18,28]. upper Victoria Nile river also reported higher DO levels to our studied rivers [7].…”

“…Comparing with other previous studies (Table 3), the concentration of TN in River Kisat was lower than those recorded by [18]. Similarly, the levels were also lower than those recorded by (27) in River Awach Kibuon but comparable concentrations in TN was reported by (28) and [21] in River Vaigai in Maduri City, Tamil Nadu, India. The concentration of TN in River Kisat was higher than those reported by [19] in Mara river, Kenya, River Nile and El-Rahawy drain in Egypt [14] implying that River Kisat is heavily polluted than Mara river and River Nile.…”

“…This is supported by a technical report by Kenya Marine and Fisheries Research Institute KMFRI [17] that documented persistent high temperatures in areas with high suspended and dissolved solids. The temperature was noted to be increasing in both river Kisat and Auji compared to [18] and [28] reported in the previous studies and also higher than what [27] reported in River Awach Kibuon (Table 3). The downstream increase in temperature in River Kisat showed a clear agreement with the findings that the maximum temperature increases downstream [36], while the maximum range is found in the midstream [34] as observed in the midstream of River Auji.…”