Kemigabo Ch., Adámek Z.
Abstract
The Mabira, Kyenshama and Rushozi valley dam reservoirs in the Mbarara District, Uganda, provide suitable environmental conditions for fishery exploitation and controlled fish
farming and/or ranching management. Physico-chemical parameters were correlated to primary production in Rushozi and Kyenshama and to altitude and geology in Mabira.
All dams were eutrophic with nitrogen likely to be limiting in Mabira and Rushozi and phosphorus in Kyenshama. Phytoplankton abundance (with Chlorophyceae and Cyanobacteria
dominance) was significantly higher in Rushozi (p < 0.05). Abundance of zooplankton and benthic macroinvertebrates was similar across dams. Nile tilapia (Oreochromis niloticus)
and African catfish (Clarias gariepinus) were the dominant and available culture species. Their condition based was highest in Rushozi dam (1.86 ± 0.18 and 0.63 ± 0.07 for
tilapia and catfish, respectively) and coincided with the highest oxygen, temperature, food uptake and phytoplankton abundance and biomass (according to chlorophyll-a
concentration). Detritus, plant material, and phytoplankton were the most important diet items for both tilapia and catfish however the level of justifiable food coincidence
(~ competition) was very low amounting to 2.9% in phytoplankton. The majority of food coincidence concerned low valued food items - detritus (12.7%) and plant material
(14.7%).
Key words:
valley dam reservoir, environment, phytoplankton, zooplankton, zoobenthos, Nile tilapia, African catfish, Mbarara district.