Browsing by Author "Patrick, Denny"

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    Evaluation of nitrogen cycling and fish production in seasonal ponds (‘Fingerponds’) in Lake Victoria wetlands, East Africa using a dynamic simulation model
    (Aquaculture Research, 2010) Kaggwa, Rose C.; Anne, A. van Dam; Kipkemboi, Julius; Patrick, Denny
    A dynamic model was developed to simulate nitrogen (N) flows and fish production in seasonal wetland fish ponds (Fingerponds) based on organic manuring and natural food production. The model incorporates pond water depth, food availability, fish stocking densities, fish and fingerling weights at stocking, reproduction rate, manure type and application rates. The ponds were fertilized fortnightly with 1042 kg ha−1 chicken manure. The model captured the dynamics of hydrology, nutrients and fish and demonstrated that similar fundamental processes underlie fish production in these systems. The model predicted annual fish yields of up to 2800 kg ha−1. Simulated fish production, chlorophyll a and dissolved inorganic N concentrations were comparable with field measurements. Using the model, N budgets and estimates of all N flows were made. Most of the N input into the ponds (60–70%) accumulated in the bottom detritus of the pond and only 8–10% was converted into fish biomass, of which about half consisted of small fish. Fish production in Fingerponds was limited by turbidity induced light limitation and by nutrient limitation. Reduction of variability of fish production should come from reduced turbidity and sufficient nutrient input to minimize light limitation and maximize fish growth.
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    Increasing fish production from wetlands at Lake Victoria, Uganda using organically manured seasonal wetland fish ponds
    (Wetlands ecology and management, 2009) Kaggwa, Rose C.; Anne, A. van Dam; Balirwa, John S.; Kansiime, Frank; Patrick, Denny
    The processes driving primary productivity and its impacts on fish production were investigated in field trials in eight seasonal earthen wetland ponds ‘Fingerponds’ (192 m2) in Uganda between 2003 and 2005. The ponds were stocked by the seasonal flood with predominantly Oreochromis spp. at densities ranging from 0.1 to 0.5 fish m−2. Chicken manure (521, 833 or 1,563 kg ha−1) was applied fortnightly. Results showed that primary productivity was enhanced with maximum average net primary productivity (±Standard Error) of 11.7 (±2.5) g O2 m−2 day−1 at the Gaba site and 8.3 (±1.5) g O2 m−2 day−1 at the Walukuba site. Net fish yields were higher in manured ponds with up to 2,670 kg ha−1 yield for a 310 day growth period compared to less than 700 kg ha−1 in unmanured ponds. Fish production was limited mainly by high recruitment, falling water levels, light limitation from high suspended solids and turbidity, and low zooplankton biomass. It was concluded that Fingerponds have a high potential for sustainable fish production and can contribute to the alleviation of protein shortages amongst the riparian communities around Lake Victoria. Production can be enhanced further with improved stock management.