The bounty of minor lakes: the role of small satellite water bodies in evolution and conservation of fishes in the Lake Victoria Region,East Africa

The Lake Victoria Region (LVR) encompasses the large lakes Victoria, Kyoga, Edward, George and Kivu, as well as scores of small satellite lakes within the parent catchments. Taken as a whole, the LVR originally harbored a unique fish fauna that included in excess of 600 endemic species of cichlid fishes. As a result of human influence, including a commercial fishery and the introduction of several exotic species, nearly 200 cichlid species and several endemic genera have become extinct from lakes Victoria and Kyoga. Recently, we have discovered that some of the apparently extinct taxa survive as extant representatives in the satellite lakes. Here, we summarize the findings of our ecological survey of the fish species of the satellite lakes. We also discuss the results of some preliminary genetic analyses, and highlight major genetic and ecological changes in the fish fauna that have taken place in the regional fishery. Minor lakes now play a crucial role in conserving the endangered species of the entire region, and also as living museums of East African ecological history. Our findings allude to the historical importance of minor satellite lakes as natural refugia for the fishes of the Lake Victoria Region, a region characterized by a history of geological and climatic instability.     

Status and impact of rural aquaculture practice on Lake Victoria basin wetlands

Rural aquaculture in Lake Victoria basin is a fast increasing nontraditional farming activity which if not appropriately practised will lead to degradation of the wetlands. As part of a study to develop appropriate guidelines and model systems for wetlands‐based rural aquaculture in the basin a survey was conducted to assess the status and the ecological and socioeconomic impact of rural aquaculture on wetlands and wetlands communities. Aquaculture practice was found to be common but not as a major activity. Aquaculture in the wetlands can be described as a low input‐low output production activity and subsistence based on ponds under 400 m² using free seed from public agencies with hardly any supplementary feeding. Men owned most of the ponds and women only contributed to the management of the fishponds by feeding the fish. Poorly constructed ponds and loss during harvesting have led to the escape of cultured species into the wild. Introduction of nonnative species in the basin has already led to wide ranging ecological, environmental and socioeconomic changes whose impact and usefulness are still very much contentious. Repeat of such scenarios can be avoided if appropriate and science‐based models for rural aquaculture farming are developed, tested and disseminated to the communities.     

Escape of farmed tilapiines into the wild and entry of wild forms in fishponds,and the possible interactions between wild and farmed tilapiines from a sample of smallholder farms in Central Uganda

Seven smallholder fishponds in central Uganda were studied between 2000 and 2001 to investigate the interaction of farmed tilapiines with their wild conspecifics. Emphasis was on the features that facilitate escape of fish and/or entry of fish into the farms and interactions between the farmed and the wild. These included number of species, source of seed, connection between pond and natural watercourses, purpose of the farm, destination of cultured fish and interaction between farmed and wild fish. Fishponds had no screens against entry of wild fish into the farm or escape of farmed fish into the wild and occurred within wetlands close to natural watercourses. Ponds stocked with one fish species were found to have multispecies with some individuals that were apparently intermediate morphs between the species. Fry produced within the growout fishponds was shared with other farmers within and outside the watersheds. This study showed that smallholder farms with little or no control of escape or entry of fish out and into the fishponds, and little or no management present circumstances that facilitate continued movement of tilapiines within and across watersheds in Ugandan waters. The study also indicated possible genetic interaction between farmed and their wild conspecifics through interactions within fishponds.     

Condition factor,Length – Weight relationship,and the fishery of <Emphasis Type="Italic">Barbus altianalis</Emphasis> (Boulenger 1900) in Lakes Victoria and Edward basins of Uganda

The condition, fishing effort and environmental parameters signify health of fish populations. This study characterized differences in water quality and fishing effort in the lacustrine and riverine systems of the River Nile, Lake Edward and Kazinga channel in Uganda. One-way Analysis of Variance (ANOVA) was used to test for differences in mean relative condition among populations in the water bodies exposed to different levels of fishing effort and water quality conditions. There were significant differences in the mean relative condition (K_n) of Barbus altianalis between River Nile (mean dif 0.0880, P <0.004) and Lake Edward and between River Nile and Kazinga channel (mean dif. 0.0796, P < 0.001). No significant difference in the mean relative condition between Kazinga channel and Lake Edward (mean diff. 0.0840, P < 0.95). Lake Edward had the highest condition (1.05), while Kazinga channel and River Nile had 1.04 and 0.96 respectively. The relationship between weight and length for each population, obtained by pooling individuals across systems was significant (P < 0.001), the length-weight allometry between the populations was also significantly different (F (2, 237) = 9.73, P < 0.001). River Nile had the highest number of fishers of 311 ± 0.88 while the number of fishers in Lake Edward and Kazinga channel were 75 ± 2.45 and 33 ± 9.12, respectively. Catch rates varied between River Nile (1.92 ± 0.59 Kg boat^-1 day^-1) and the rest of the systems, 6.20 ± 1.86 and 6.85 ± 1.49 Kg boat^-1 day^-1 in Lake Edward and Kazinga channel respectively. Water quality varied greatly across all the water bodies. Dissolved oxygen was below the minimum of 5 mgl^-1 required for the physiology of freshwater fish. Conductivity was highest in Lake Edward (312 µS cm^-1), followed by Kazinga channel and least in River Nile. The consistent variation in condition, fishing effort and water quality, indicates differential selective pressures faced by B. altianalis in the systems and therefore calls for concerted efforts for appropriate management measures.