Mwebaza-Ndawula, L.M., V. Kiggundu & W. Pabire Ghandi. (2003). Diversity and abundance of invertebrates in the Victoria basin lakes and their role in fishery production. Uganda Journal of Agricultural Sciences. 8:209-220.

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Mwebaza-Ndawula, L.M., V. Kiggundu & W. Pabire Ghandi

2003

8:209-220.

Publication

Available for editors   [request]

A field study was carried out on zoplankton communities in the Victoria basin lakes (Victoria, Nabugabo lakes, Koki lakes and Wamala) between 1997 and 2001. The objective of the study was to determine the composition, distribution and abundance ofzooplankton and their role in fishery production. Field sampling was carried out once every quarter in selected inshore and offshore areas of the lakes. Samples were taken with Nansen type nets 01'0.25 m mouth opening and -0-100 urn mesh opening and a 5-litre Schindler trap. A total of 50 species was recorded within the basin lakes. Rotifers had the ~ighest diversity with 13-22 species. Cyclopoids contained 7, Calanoids 2, and ladocerans 9 species. The most widely distributed species were TlIer/llocyclops lIeglectlls, Moilla micrura and several rotiferan species. Rotifers were numerically most abundant in lakes Mburo, Kaehera, Nabugabo and Wamala while copepods dominated in Vietoria-Sio, Kayugi and Kayanja. However, eopepods had the highest dry weight in all the basin lakes. In Lake Victoria, copepods dominated the communities both inshore and offshore, while rotifers were nearly non-existent offshore. A historical perspective showed higher abundance of Calanoids and Cladoccrans during the 1960s than in the 1990/2000 communities. These changes are believed to be associated with drastic changes in lake trophy and fish faunal composition over the last four decades. Higher zooplankton densities offshore occurred in the Victoria, Nabugabo and Karhera. Species diversity was higher offshol'e in Vicloria-Sio, Nabugabo and Wamala. Seasonal abundance in Lake Victoria showed peak abundance during May, coinciding with the onset ofthe annual mixing period. Copepods dominated in the diets of Rastrilleoboltl argelltea (Mukene) and larval Lates "itotiells (Mputa) while larval cichlids consumed a proportional mix ofcopepods, Cladocera and aquatic insect larvae. Lakes with high abundance of relatively large-bodied copepods, C1adocerans and aquatic insect larvae are rated high in fishery production than those dominated by small-bodied rotifers. The latter lakes are generally eutrophic (over-fertilised) water bodies, where the invertebrates' fish food environment is no longer favourable for fishery production. There is need to put in place measures to mitigate increasing eutrophication of water bodies within the Victoria basin area in order to ensure stable food environment for sustained fishery production.

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