Fringing wetlands on the northern shores of Lake Victoria, Uganda and their potential for fish culture

Fingerponds are earthen ponds dug at the edge of a wetland and stocked naturally during flooding. Fingerponds aim at enhancing fish production from wetlands with minimal impact on their natural functions. This study investigated the base-line conditions of the ponds and surrounding wetland prior to the formulation of management strategies. Eight 192 m 2 ponds were constructed in two papyrus wetlands on the northern shores of Lake Victoria, Uganda. The ponds were naturally stocked predominantly by Oreochromis spp . during the May to June 2003 rains. Between February’ 2002 and September 2003, factors determining the natural dynamics and functioning of the Fingerponds and their potential for fish production were examined. Key ecological processes affecting water quality in the ecotone and the ponds were the buffering capacity, and in the ponds themselves sedimentation/re-suspension. The water quality in the ponds was stable and showed little seasonal or spatial variation. Pond water pH values ranged from 5.3 to 9.4, temperatures from 20 to 30 °C, dissolved oxygen from 2.0 to 17.8 mg L * and ammonium nitrogen from 0 to 3.6 mg L ‘. Low nutrient concentrations in the ponds resulted in low phytoplankton biomass. Zooplankton colonization of the ponds was poor resulting in low biomass. Flood events determined the type and size of fish in the ponds. Initial fish stock biomass at the onset of the 2003 growout period ranged between 93 and 97 kg ha” 1 . It was deduced that with enhancement of nutrient levels, Fingerpond systems have potential and can be of real benefit as a source of protein to poor, riparian communities.