Effects of Phytoplankton and water quality dynamics on Nile Tilapia in earthen ponds at KMFRI Kegati Aquaculture Centre in Kisii County

Aquaculture is the future bridging gap for the declining capture fisheries. Fish farming in Kenya is currently on the increase according to recent overview survey. In the effort to increase production in ponds there was need to investigate the water quality and algal biodiversity since they play a good role in the aquatic food chain. An investigation, carried out from October 2015 to 2018 showed that Physico-chemical parameters (turbidity, temperature, conductivity, alkalinity, dissolved and suspended solids, and dissolved oxygen concentration) were measured insitu. Chlorophyll a and phytoplankton analyses were done using spectrophotometric and microscopy techniques respectively. There were significant spatial differences in the dissolved oxygen concentrations (p<0.0001) within the ponds. These differences were pronounced at the Pond B, Pond E and Pond F respectively. The differences were associated with the stocking density and feeding regimes. Chlorophyll concentrations were found to be higher during the dry season compared to the rainy season. This could be attributed to high turbidity during the rainy season, which reduces light penetration into the water column. Diatom family 60 %, and was the most abundant group followed by Chlorophyceae (28%), Euglenophytes (11%), Zygnemetaphaceae family (7 %), Euglenophyceae (4%) and Cyanophyceae. Among the diatoms the most dominant species were Amporas sp., Cyclotella sp., Synedra sp and Surillella sp. Significant differences in distribution patterns in phytoplankton were observed between the Pond A to Pond F. Phytoplankton quotient (PQ) value was estimated at 4.1±0.26 indicating that the ponds is highly eutrophic. These results are useful in the formulation of management advice to stakeholders