Phytoplankton and water quality dynamics in earthen ponds for Nile Tilapia culture at Lubukhwas Fish Farm, Kakamega County, Kenya

Pond aquaculture is expanding in Kenya to offset declining capture fisheries, yet water quality and phytoplankton dynamics in these ponds remain understudied. This study assessed physicochemical parameters and phytoplankton community structure in six earthen ponds (A–F) at Lubukhwas Fish Farm, Kakamega County from October 2023 to November 2024. In situ measurements included turbidity, temperature, conductivity, alkalinity, total dissolved and suspended solids and dissolved oxygen (DO). Chlorophyll-a was determined spectrophotometrically, and phytoplankton were identified microscopically. Significant spatial differences in DO were observed among ponds (p<0.0001), with pronounced variation in ponds B, E and F attributed to differences in stocking density and feeding regimes. Chlorophyll-a concentrations were higher during the dry season than the rainy season, likely due to reduced light penetration from elevated turbidity during rains. Diatoms dominated the phytoplankton community (60%), followed by Chlorophyceae (28%), Euglenophyceae (11%), Zygnematophyceae (7%) and Cyanophyceae (<5%). Dominant diatom genera included Amphora, Cyclotella, Synedra and Surirella. Phytoplankton distribution patterns differed significantly across ponds (p<0.05). The phytoplankton quotient (PQ) averaged 4.1±0.26, indicating highly eutrophic conditions. These findings highlight the influence of management practices on pond water quality and algal communities and provide a basis for optimizing feeding regimes, stocking densities, and aeration strategies to sustain tilapia production while minimizing eutrophication risks.