NRU :: Browsing by Author "Waiswa Mwanja, Wilson"

Browsing by Author "Waiswa Mwanja, Wilson"

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Comparison of the genetic and ecological diversity of the native to the introduced tilapiines (Pisces: Cichlidae), and their population structures in the Lake Victoria region, East Africa
(Aquatic Ecosystem Health & Management, 2010) Waiswa Mwanja, Wilson; Kaufman, Les; Fuerst, Paul A.
The impact of introduced tilapiines in Lake Victoria Region (LVR) was studied using experimental fishing survey methods and microsatellite DNA marker analysis. The experiments were carried out between 1993 and 2000. Oreochromis esculentus and O. variabilis, the two native forms of the LVR and original principals of the fisheries of these waters, were found to be completely displaced from the major lakes and were only occasionally found in a few minor satellite lakes surrounding Lakes Kyoga and Victoria. Nile tilapia, O. niloticus, is now the dominant tilapiine, and one of the three key fisheries species of LVR along with Nile perch, Lates niloticus, and the minnow-like Rastrineobola argentea. Oreochromis leucostictus, also introduced to the LVR from the nilotic system, was largely restricted to swampy fringes of LVR water bodies. Tilapia zillii, also introduced from nilotic waters and earlier recorded to have been the most prevalent introduced tilapiine in LVR, occurred only sparsely and was very restricted in distribution. Genetic studies showed Nile tilapia having the highest genetic diversity, and being the least subdivided among LVR tilapiines. O. leucostictus was next in variability, but had the greatest gene flow, probably due to its ability to traverse low oxygen waters such as swamps which separate most LVR water bodies. The native forms were genetically the least variable, except where they coexist with introduced congeners. ‘Uncontaminated’ native forms were observed only in satellite Lakes of Kayanja, Kayugi, Manywa, Kawi and Kanyaboli. The population structure of native forms of LVR suggest they are being genetically swamped, especially for O. variabilis by Nile tilapia alleles, due to genetic exchange with introduced forms, resulting in highly localized differentiation of native species. T. zillii was equally highly subdivided, but has higher genetic variation within subpopulations, a situation linked to monogamous breeding behaviour which allows most individuals of its population to participate in breeding. Hybridization with T. rendalli, which was only occasionally encountered and previously mistaken for dwarf Nile tilapia, may also contribute to high within population variation in small T. zillii populations. On a macro-evolutionary level, the sister relationship between O. niloticus and O. esculentus is questionable and in need of further phylogenetic analysis. Overall the study showed a changed fishery, and the need to manage satellite lakes in a manner that will preserve the previous premier elements of the region’s fishery (O. esculentus and O. variabilis) within natural refugia.
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
(African Journal of Ecology, 2009) Tenywa Mwanja, Matthew; Waiswa Mwanja, Wilson
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.
Evolutionary history of Nile perch Lates sp. inferred from mitochondrial DNA variation analyses
(Zoological Studies, 2013) Mwanja, Matthew T.; Muwanika, Vincent B.; Masembe, Charles; Nyakaana, Silvester; Waiswa Mwanja, Wilson
Evolutionary histories of aquatic species are often characterized by distinct patterns of genetic variation, which in part reflect drainage evolution. In the present study, the consequences of paleo-environmental changes on patterns of genetic variation of the mitochondrial DNA control region in Nile perch Lates sp. sampled from seven water bodies across the African continent were investigated. Results: In a total sample of 124 individual sequences, 37 distinct haplotypes were observed, and 78.4% of these haplotypes were location specific. Haplotypes were found to cluster into two major groups, one composed of individuals sampled from East Africa and another from West Africa, with no haplotypes shared in between. Conclusion: These lineages may have developed in geographical isolation during the Pleistocene and have remained largely allopatric without gene flow (Nm = 0.0) since that time. There was also evidence that both of these genetic lineages have undergone recent population expansions. We interpret these results in light of the recent evolution of Africa's modern drainage network.
Freshwater fish seed resources in Uganda
(FAO Fisheries Technical Paper, 2007) Waiswa Mwanja, Wilson
The aquaculture sector in Uganda has started to grow very rapidly during recent years with the commercialization approach taken by the government. Aquaculture is now seen not only as source of dietary protein but also as a means of generating income through improved productivity and managing aquaculture production as a business venture. This has attracted a new class of farmers.The issues of fish seed availability and quality have become a major challenge. This new trend has made the government to turn to private sector for improved supply of the required quality and to meet the needed quantity of fish seed. Fish seed propagation in Uganda was, until the late 1990s, a remit of the public sector. Currently there are nearly 50 private fish hatcheries ranging from small- to medium-scale with a few large commercial operation. The country’s projection for meeting the aquaculture and stock enhancement seed requirements is about 450 million fingerlings annually. The general plan is to meet this demand through privately-owned and operated fish hatcheries. Use of the private sector calls for trained manpower and exposure to appropriate technology. There is also urgent need to improve broodstock management skills and to initiate breeding programmes for improvement of the productivity of key aquaculture species. Although government has established some regulations under the “Fish (Aquaculture) Rules 2003” to regulate fish seed production and distribution, there is still a need for technical assistance to review and develop clear and implementable standards and guidelines for the private fish hatchery owners and operators in Uganda.
Genetic evidence of successful establishment of the Nile perch (Lates spp. L.) in East African lakes and implications for management
(Management of Biological Invasions, 2012) Mwanja, Matthew T.; Waiswa Mwanja, Wilson; Muwanika, Vincent B.; Masembe, Charles; Nyakaana, Silvester
Nile perch establishment in novel ranges in East Africa is one of the most successful freshwater invasion stories in the recent history. It became ecologically dominant and well established in several lakes in the Lake Victoria Region in a period of less than 5 decades. Genetic diversity of both introduced and native populations were assessed and patterns compared in order to establish the genetic consequences of their introductions. Genetic variation was surveyed at both the mitochondrial control region (CR) and at nine microsatellite loci. A total of 527 Nile perch fish were sampled from 5 East African lakes: native source populations were examined from lakes Albert and Turkana while introduced populations were sampled from lakes Kyoga, Nabugabo and Victoria. Both types of markers revealed higher average genetic diversity for invasive species (HE = 0.70, h = 0.81) than for native source populations (HE = 0.66, h = 0.69). Both populations scored relatively higher than the average for freshwater fishes (HE = 0.62). Both native and introduced populations had 2 underlying genetic groupings in similar proportions as revealed by the STRUCTURE program. The high genetic diversity was most probably a consequence of higher numbers of propagules than outlined by official records of introductions. Use of high number of individuals at stocking is probably the reason for apparently minimized ‘founder effects’ of Nile perch in the introduced ranges. The two underling populations revealed through genetic analysis may be representatives of the two subspecies of Nile perch previously reported in other studies. Implications to the management of this fishery in the East African region is that with the relatively high genetic diversity, the species could be sustainably exploited if it were effectively managed. In addition, further studies of the life histories and other attributes of the two genetic groupings of Nile perch in the region are recommended, as they may require different management plans.
Genetic viability of Nabugabo lakes (LVR satellite lakes) fish species
(Wetlands Inspection Division, 2001) Waiswa Mwanja, Wilson
Natural populations of fish species in Lake Victoria Region (LVR) have under gone dramatic changes including severe reduction in sizes, division of original stocks into disjunct subunits, and segregation into several isolated population units either within a single water body or even worse into separate waters. In addition, these changes have been either preceded or precipitated by introductions of non-indigenous species that outcompeted the native forms and in case of closely related species genetically swamped them through hybridisation. The latter is especially the case in Nabugabo Jakes. Such events lead to fragmentation of populations, which results in reduction in genetic diversity due to genetic drift, inbreeding and reduced or lack of gene flow among independent units. Such phenomena make the continued existence of fisheries stocks in the wild precarious, more so in the face of the competition from exotic species. Species introductions coupled with growing exploitation pressure of the fisheries ofthese lakes have put the native stocks at risk. Nabugabo lakes harbour cichlid species that are unique to these lakes more so species of the cichlid complex. In this paper the ecological status and genetic viability of key Nabugabo lakes fish species is examined and management options are discussed.
Preliminary results of the analysis of the population structure of the Nile perch (Lates niloticus linnaeus, 1758) of Lake Victoria using microsatellite markers
(African Journal of Biotechnology, 2008) Tenywa Mwanja, Matthew; Waiswa Mwanja, Wilson
Preliminary results are provided of a study instituted to analyze the genetic population structure of the Nile perch in Lake Victoria since 2002. 293 individuals from six geographically distinct locations within the lake were analyzed using two polymorphic microsatellite DNA markers. Tests for differentiation with an overall FST = 0.03 (P < 0.05) suggested that populations were genetically differentiated, with the closet population pairs Nyaburu-Rubafu and Mirunda-Maboko as the most differentiated populations. There was an extensive gene flow between the populations (Nm = 20.77). The overall gene diversity (0.17) was low. All the results point to the fact that Nile perch was only recently introduced species in the lake based on a small founder population, which though slow in establishing later exploded to become the most dominant species in the lake. On the whole the two loci indicate some level of differentiation between locations; however, the levels of genetic differentiation shown by the two loci were not enough to define the structure of Nile perch stocks, and assess the level of exchange between locations. Further work is underway using bigger number of microsatellite markers.
Status and impact of rural aquaculture practice on Lake Victoria basin wetlands
(African Journal of Ecology, 2007) Waiswa Mwanja, Wilson; Akol, Anne; Abubaker, Laila; Mwanja, Matthew; Msuku, Scot Batman; Bugenyi, Fred
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.

Browsing by Author "Waiswa Mwanja, Wilson"

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