The effects of livestock manure on nutrient dynamics, water quality and fish yields in seasonal wetland fish ponds (Fingerponds) at the edge of Lake Victoria, Kenya

This chapter reports the results of pond aquaculture dynamics of experimental integrated aquaculture ponds (Fingerponds) at the Lake Victoria wetlands in Kenya. Fingerponds are self-stocked flood-based fish ponds at the wetland margin. The overall aim of the study was to develop and evaluate low-cost production systems to enhance the wetland fishery at subsistence level. The ponds were stocked adequately with diverse fish species at densities of 3 to 10 fish m -2 . The effects of livestock manure applications on nutrient dynamics, water quality and fish yields were studied. There was no observable adverse effect of manuring on pond water quality. Regression analysis indicated that site, pond management (manuring) and the environmental and climatic variables explained a large part of the variation in NH 4 -N, NO 3 -N and total nitrogen concentrations with adjusted r 2 of 0.64, 0.70 and 0.65, respectively. The explained variance for o-PO 4 and total phosphorus was 58% and 61%, respectively. Manuring increased the total phosphorus concentration in the sediment but only had marginal effects on total nitrogen. The chlorophyll a concentration was higher in manured ponds, reaching an average of 150 µg l -1 compared to an average of 27 µg l -1 in un-manured ponds. The net fish yields were highly variable between sites and seasons and ranged from 402 to 1069 kg ha -1 , the data showing that manuring was advantageous. The duration of the culture period, site variability and manuring explained 82% of the variation in fish yields. Careful fertilization of the ponds with livestock manure can be used to improve fish yields in Fingerpond systems.