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Lake Victoria is vulnerable to increasing eutrophication, which has become manifested in ecological changes not yet fully understood. From October 2009 to January 2010, the influence of water quality on zooplankton community structure in three habitats in northern Lake Victoria, including sewage lagoons at the lake shores, Napoleon Gulf (NG) and the interface between the lake and the Nile River (also known as Source of the Nile River), was examined. Selected physico-chemical parameters (dissolved oxygen concentration; water temperature; electrical conductivity; water depth) were measured in-situ, while water samples were collected for chlorophyll-a determinations. Zooplankton was sampled with conical plankton net (mesh size 60 μm; 0.25-m mouth diameter). The NG and Source of the River Nile (SN) sampling sites exhibited significantly higher species richness, relative to the Sewage Lagoons (SL) site ( F2,69 = 68.533; P < 0.05). Higher mean densities and dry biomass of zooplankton was generally a characteristic of the SL site (8715 ± 3241 ind L−1; 1862 ± 451 μg L−1), compared to the NG (119 ± 24 ind L−1; 53 ± 8 μg L−1) and SN sites (151 ± 26 ind L−1; 58 ± 9 μg L−1). Copepoda constituted a high numerical composition of the zooplankton at the NG and SN sites (>90% for both sites), while Rotifera dominated the zooplankton community at the SL site (97%). The mean values (±SE) of soluble reactive phosphorus (4060.7 ± 776.6 μg L−1) and nitrate-nitrogen (2121.7 ± 355.5 μg L−1) were much higher for the SL site, compared with the SN (8.2 ± 1.1 μg L−1; 28.6 ± 5.3 μg L−1, respectively), and NG site (7.8 ± 0.8 μg L−1; 32.7 ± 5.4 μg L−1, respectively). This study indicated the nutrient-rich conditions observed at the SL site suppress the zooplankton species diversity, but favour species-specific abundance and biomass. These study results indicate the zooplankton community structure can be used as a biological indicator of water quality in the Lake Victoria region. [ABSTRACT FROM AUTHOR]

The stable isotopes of nitrogen ( δ15N) and carbon ( δ13C) provide powerful tools for quantifying trophic relationships and carbon flow to consumers in food webs; however, the isotopic signatures of organisms vary within a lake. Assessment of carbon and nitrogen isotopic signatures in a suite of plants, invertebrates, and fishes in Lake Kyoga, indicated significant variation between two sites for δ13C (paired t = 6.305; df = 14, P < 0.001 and δ15N paired t = 1.292; df = 14; P < 0.05). The fish fauna in Bukungu was generally more 13C enriched (mean δ13C = –16.37 ± 1.64‰) than in Iyingo (mean δ13C = –20.80 ± 2.41‰) but more δ15N depleted (mean δ15N = 5.57 ± 0.71‰) than in Iyingo (mean δ15N = 6.92 ± 0.83‰). The simultaneous shifts in phytoplankton and consumer signatures confirmed phytoplankton as the major source of carbon for the food chain leading to fish. Limited sampling coverage within lakes may affect lake wide stable isotope signatures, and the same error is transferred into trophic position estimation. Consideration of potential intra-lake spatial variability in isotope ratios and size is essential in evaluating the spatial and trophic structure of fish assemblages. [ABSTRACT FROM AUTHOR]

Abstract: Despite ongoing preventive chemotherapy campaigns, intestinal schistosomiasis is hyper-endemic in shoreline communities living along Lake Albert, Uganda. To provide a deeper insight into the local epidemiology of Schistosoma mansoni, a variety of field-based studies were undertaken focusing upon schistosome–snail interactions and confirmation of transmission foci. Cercarial shedding patterns of field-caught Biomphalaria spp., as identified by morphology, were hourly observed over a ten day period and showed that Biomphalaria stanleyi produced significantly more cercariae than Biomphalaria sudanica. Peak production times in both species were between 12.00 and 14.00h indicating greatest infection risk from lake water exposure is during the early afternoon. Laboratory-bred snails were exposed to locally hatched miracidia and susceptibility of Biomphalaria spp. was confirmed experimentally. Biomphalaria stanleyi was a more permissive host. After ascertaining appropriate conditions for infection of laboratory mice, 28 groups of between 5 and 6 naïve mice were placed in floatation cages at four suspected shoreline transmission sites for a 30 minute period of exposure. Eight weeks later, mice (n =142) were culled and S. mansoni adult worms were retrieved from 10 animals. Taken as a whole, these observations highlight the local importance of B. stanleyi in transmission of intestinal schistosomiasis and clearly demonstrate the risk of infection on the Lake Albert shoreline. To mitigate this risk local environmental modification(s), i.e. improvement in sanitation and hygiene and control of snail populations, is needed to bolster the impact of chemotherapy-based interventions. [Copyright &y& Elsevier]

In this study, we compare the diet, life history characters and abundance of Nile tilapia ( Oreochromis niloticus) stocks between two crater lakes in western Uganda (Lake Nyamusingiri and Lake Kyasanduka) that differ in their history of fishing pressure. Both lakes support native fish communities, but also harbour populations of introduced O. niloticus. Lake Nyamusingiri was characterized by a higher relative and absolute abundance (CPUE) of haplochromine cichlids and a lower abundance of O. niloticus than in Lake Kyasanduka. In addition, the O. niloticus population in Lake Nyamusingiri exhibited a smaller mean size and a lower relative abundance of juveniles than in Lake Kyasanduka. These differences may reflect, at least in part, heavy exploitation of O. niloticus in this lake, as compared with Lake Kyasanduka where fishing was banned in 1988. In both lakes, the maximum size and size at maturity was small relative to other larger water bodies in the region. The Nile tilapia in both lakes were primarily herbivorous; with phytoplankton dominating the diet. In general, the condition of O. niloticus in the crater lakes was low relative to other larger lakes in the region. The low catch per unit effort of O. niloticus in Lake Nyamusingiri (7.8%) relative to Lake Kyasanduka (54.9%) suggests that overexploitation of the fishery is occurring, calling for careful monitoring and management of the system. [ABSTRACT FROM AUTHOR]

In Eastern Uganda, paddy-rice growing, which has only become popular in recent years, seems to be associated with the emergence of schistosomiasis mansoni as a new problem in public health. To estimate the magnitude of this problem, a cross-sectional, baseline survey was carried out in six villages of the Kibimba Rice Scheme. The overall prevalence of Schistosoma mansoni infection was found to be 20%. The highest prevalences and intensities of infection were seen in those aged 5-29 years, with more males infected than females. An attempt was then made to identify the important factors in the aetiology of S. mansoni in this area. Odds ratios indicated that working regularly in the rice paddies, fishing with baskets, and being male were statistically associated with an increased risk of S. mansoni infection. It is clear that schistosomiasis mansoni which is emerging as a new health problem in the study area is closely linked to working in the rice paddies. Encouraging the rice farmers to wear knee-high, waterproof boots while in the fields may help control the disease.