Recent Submissions

  • Fishing gear selectivity for Lates niloticus L., Oreochromis niloticus L. and Rastrineobola argentea P. in Lakes Victoria, Kyoga and Nabugabo

    Ogutu-Ohwayo, R.; Wandera, S.B.; Kamanyi, J.R. (1998)
    Catch effort data on which fisheries management regulations are sometimes based are not available for most lakes inUganda. However, failure to regulate fishing gears and methods has been a major cause of collapse of fisheries in the country. Fisheries have been damaged by destructive and non-selective fishing gears and methods such as trawling andbeach seining, by use of gill nets of mesh size which crop immature fish and by introduction of mechanised fishing. Selectivity of gears used to crop Lates niloticus L.(Nile perch), Oreochromis niloticus L. (Nile tilapia) and Rastrineobola argentea Pellegrin (Mukene) which are currently the most important commercial species in Uganda were examined in order to recommend the most suitable types, sizes and methods that should be used in exploiting these fisheries. Gill nets of less than 127 mm mainly cropped immature Nile tilapia and Nile perch. To protect these fisheries, the minimum mesh size of gill nets should be set at 127 mm. Seine nets of 5 mm caught high proportions in immature Mukene while those of 10 mm caught mainly mature Mukene. When operated inshore, both sizes caught immature Nile perch and Nile tilapia as by-catch. To protect the Mukene fishery and avoid catching immature bye-catch, a minimum mesh size of the Mukene net should be 10 mm operated as Lampara type net offshore, but since most fishermen have been using 5 mm seine nets for over five years the minimum size should not be allowed to drop below 5 mm pending further thorough investigations. Beach seining and trawling are destructive to fisheries and should be prohibited until data that may justify their use is available.
  • Variation in composition of macro-benthic invertebrates as an indication of water quality status in three bays in Lake Victoria

    Sekiranda, S.K.; Okot-Okumu, J.; Bugenyi, F.W.B.; Ndawula, L.M.; Gandhi, P. (2004)
    Knowledge of how biota can be used to monitor ecosystem health and assess impacts by human alterations such as land use and management measures taken at different spatial scales is critical for improving the ecological quality of aquatic ecosystems. This knowledge in Uganda is very limited or unavailable yet it is needed to better understand the relationship between environmental factors at different spatial scales, assemblage structure and taxon richness of aquatic ecosystems. In this study, benthic invertebrate community patterns were sampled between June 2001 and April 2002 and analysed in relation to water quality and catchment land use patterns from three shallow near-shore bays characterized by three major land uses patterns: urban (Murchison Bay); semi-urban (Fielding Bay); rural (Hannington Bay). Variations in density and guild composition of benthic macro-invertebrates communities were evaluated using GIS techniques along an urban-rural gradient of land use and differences in community composition were related to dissolved oxygen and conductivity variation. Based on numerical abundance and tolerance values, Hilsenhoff's Biotic Index ofthe invertebrates was determined in order to evaluate the relative importance of water quality in the three bays. Murchison Bay supported a relatively taxa-poor invertebrate assemblage mainly comprising stenotopic and eurytopic populations of pollution-tolerant groups such as worms and Chironomus sp. with an overall depression in species diversity. On the contrary, the communities in Fielding and Hannington bays were quite similar and supported distinct and diverse assemblages including pollution-intolerant forms such as Ephemeroptera (mayflies), Odonata (dragonflies). The Hilsenhoff Biotic Index in Murchison Bay was 6.53. (indicating poor water quality) compared to 6.34 for Fielding Bay and 5.78 for Hannington Bay (both indicating fair water quality). The characterization of maximum taxa richness balanced among taxa groups with good representation of intolerant individuals in Hannington Bay relative to Fielding and Murchison bays concludes that the bay is the cleanest in terms of water quality. Contrary, the dominance of few taxa with many tolerant iqdividuals present in Murchison Bay indicates that the bay is degraded in terms of water quality. These result are ofimportance when planning conservation and management measures, implementing large-scale biomonitoring programs, and predicting how human alterations (e.g nutrient loading) affect water ecosystems. Therefore, analysis of water quality in relation to macro-invertebrate community composition patterns as bio-indicators can lead to further understanding of their responses to environmental manipulations and perturbations.
  • Common fish diseases and parasites affecting wild and farmed tilapia and catfish in central and western Uganda

    Walakira, J.K.; Akoll, P.; Engole, M.; Sserwadda, M.; Nkambo, M.; Namulawa, V.; Kityo, G.; Musimbi, F.; Abaho, I.; Kasigwa, H.; et al. (2014)
    Intensification of aquaculture production in Uganda is likely to result into disease out-breaks leading to economic losses to commercial fish farms and associated natural aquatic ecosystems.This survey assessed health profiles of selected commercial fish farms and adjacent natural aquatic ecosystemsto identify fish diseases and parasites affecting Nile tilapia (Oreochromis niloticus) and African catfish (Clarias gariepinus) in aquaculture systems in Uganda. Fish farmsencounter disease out-breaks that cause low survival rates (0 - 30%), especially catfish hatcheries.Health management issues are not well understood by fish farmers, with some unable to detect diseased fish. Current control strategies to control aquatic pathogens include use of chemotherapeutants and antibiotics. Bacterial pathogens isolated included Flavobacterium columnare,Aeromonas sp., Edwardsiella sp., Psuedomonus sp., Steptococcus sp., Staphylococcus sp., Proteus sp.,and Vibrio sp. A high occurrence of Flavobacterium columnare exists in both asymptomatic andsymptomatic fish was observed. Parasites included protozoans (Ichthyopthirius multiphilis,Trichodina sp. and Icthyobodo sp.) and trematodes (Cleidodiscus sp. and Gyrodactylus sp.). Diagnosisand control of diseases and parasites in aquaculture production systems requires adoption of a regional comprehensive biosecurity strategy: the East African (EAC) region unto which this study directly contributes.
  • Proximate composition and mineral contents of pebbly fish, Alestes baremoze (Joannis, 1835) fillets in relation to fish size

    Kasozi, N.; Degu, G.I.; Asizua, D.; Mukalazi, J.; Kalany, E. (2014)
    Alestes baremoze (Joannis, 1835), locally known as Angara in Uganda, is native to fresh watersystems in Africa, thriving well in both lacustrine and riverine conditions. It is part of the routinediets of families in northern Uganda, South Sudan, the Sudan and the Democratic Republic ofCongo. The objective of this study was to determine the proximate composition and mineralcontents of A. baremoze fillets according to fish size. The mineral contents of A. baremoze fromLake Albert were analysed using standard procedures. The fish samples were categorised intothree size-groups; <1 kg (880–990g), 1-1.5 kg and 1.6-2.5 kg. On wet weight basis, there were nosignificant differences (p>0.05) in crude protein and ash content among the different fish sizes.However, there were significant differences (p<0.05) in crude fat, carbohydrate, gross energy andvitamin A. Crude fat (0.35%), carbohydrate (0.37%) and gross energy (597.6 Kcal/100 g) weresignificantly higher in medium sized fish (1 to 1.5 kg) compared with the larger fish category.Vitamin A contents of different fish sizes ranged from 55.1 to75.3 μg RAE/100g. The contents ofmagnesium and iron were highest in sizes <1 kg (5.34 mg/100 g) and (3.58 mg/100 g), respectively.It was observed that potassium content (339.33 mg/100 g) and calcium (29.75 mg/100 g) weresignificantly higher (p<0.05) in fish >1.5 kg. These findings suggest that taste, freshness andother related external appearances should not be the only factors to be considered in making choice for marketing and consumption of Alestes baremoze.
  • Reduction of the “ngege”, Oreochromis esculentus (Teleostei: Cichlidae) populations, and resultant population genetic status in the Lake Victoria region

    Mwanja, W.W.; Fuerst, P.A.; Kaufman, L. (2012)
    Ngege, Oreochromis esculentus, originally formed the mainstay of the Lake Victoria Region (LVR) fisheries. Together with its indigenous congener O. variabilis, it was displaced from Lakes Victoria and Kyoga of LVR and was found to survive as isolated small populations within the peripheral minor lakes and reservoirs around the two lakes. Displacement of the two LVR indigenous tilapiines was thought to be principally driven by changed lake environment and predation by the introduced Nile perch, but also competition and genetic swamping by the closely related introduced and comparatively more ecologically versatile tilapine species. In a study carried out in the LVR between 1993 and 2003, micro satellites and RAPD markers were used to analyse the remnant populations so as to establish the population structure and extant genetic diversity of O. esculentus.Analyses indicated that the surviving O. esculentus retained a high proportion of genetic diversitywith high differentiation between units an indication of genetic exchange between indigenous and introduced Nile tilapia where the two forms co-existed. While this heightened concern for genetic swamping of the remnant population units by the introduced tilapiines it was noteworthy that in a few of the satellite lakes where the O. esculentus was dominant evidence for introgressionwas weak.
  • Culturing the African lungfish in Uganda: effects of exogenous fish feed on growth performance in tanks

    Walakira, J.K.; Molnar, J.J.; Phelps, R.; Terhune, J. (2014)
    The availability of African lungfish (Protopterus aethiopicus) in many communities in Uganda is declining. Indigenous efforts to culture this fish usually produce poor yields and depend on feeding fish fry, minced meat, and leftover food. This study evaluates three formulated diets (diet-1, diet-2, diet-3) fed to wild caught lungfish fingerlings reared in indoor tanks for 77 days.Experimental fish gradually accepted sinking pellets, and marginal increases in average body weight were observed. Mean (± SE) final weight (15.86 ± 0.80 g) for fish fed on diet-3 was significantly higher (p < 0.05) than fish fed diet-1 and diet-2. Specific growth rates (SGR) for diet-3 were significantly higher (p < 0.05) than diet-1, and marginally more than diet-2 (0.37 ± 0.04 %/d). Feed conversions were similar (p >0.05), ranging from 1.61 ± 0.26 to 2.07 ± 0.11. Survivals afteran 11-week culture were relatively low (< 60%), but generally increased (R2 = 0.667, P = 0.007)with increasing dietary proteins. Diet-3 had a significant higher survival rate (p< 0.05) than diet-1 and diet-2. Significant growth performance was attained with diet-3. This study demonstrated that sinking fish feed pellets can be used to culture wild-caught African fingerlings in captivity.
  • The decline of Alestes baremose Boulenger, 1901 and Hydrocynus forskahlii (Cuvier, 1819) stocks in Lake Albert: implications for sustainable management of their fisheries

    Nakiyende, H.; Mbabazi, D.; Taabu-Munyaho, A.; Bassa, S.; Muhumuza, E.; Efitre, J. (National Agricultural Research Organisation, (NARO)Entebbe, Uganda, 2013)
    The fish stocks of Lake Albert face immense exploitation pressure which has led to “fishingdown” of their fisheries, with some larger species having been driven to near-extinction, while others such as Citharinus citharus have almost disappeared. Both A. baremose (Angara) and H. forskahlii (Ngassia) historically formed the most important commercial species in Lake Albert until the early 2000s but recent Catch Assessment Surveys (2007-2013) revealed a sweeping decline in their contribution to the commercial catch from 72.7% in 1971 to less than 6% in 2013.The catch per unit effort also registered a two-fold decline from 45.6 and 36.1 kg/boat/day to 22.6and 18.1 kg/boat/day for A. baremose and H. forskahlii respective between 1971 and 2007. Over 50% of illegal gillnets, below the legal minimum limit of four inches (101.6 mm) used on Lake Albert target the two species. Gillnet experiments found the three inch (76.2 mm) gill net mesh size suitable for sustained harvest of the two species. The study concludes that optimal utilization of the two species and probably other non target fish species is achievable through species specific management strategies, coupling species specific licensing, and controlling harvest of juvenile individuals, overall fishing effort and fish catch on Lake Albert and protecting the vulnerable fish habitats.
  • The effect of artisanal preservation methods on nutritional security of “Mukene” Rastrineobola argentea caught from Lakes Victoria and Kyoga in Uganda

    Masette, M.; Kwetegyeka, J. (National Africultural Research Organisation, (NARO)Entebbe, Uganda, 2013)
    The artisanal fish preservation methods in Uganda are characterized by extreme operatingconditions. Consequently, vital nutritional components diminish in value and quantity whichrenders fish consumer nutritionally insecure. To establish the magnitude of nutritional loss,duplicate samples of Mukene Rastrineobola argentea were collected from Kiyindi landing site onL. Victoria and Moone landing site on L. Kyoga. Each set of duplicate samples was divided into fiveportions and kept on ice. For each preservation method a portion was processed into respective products at Food Bioscience and Agri-Business Laboratories aside from the control (fresh) sample.Both preserved and control samples were analysed for nutrient loss at Department of Chemistry, Makerere University using AOAC methods. The composition of fatty acids was determined by methanolysis gas chromatography and Mass spectrophotometry of the resultant methyl esters.The results indicate that nutrients of all preserved samples did not vary significantly from thecontrol except for some fatty acids. The Eicosapentaenoic acid (EPA) in fresh samples declinedfrom 6.72% to 1.08% in deep-fried samples constituting 83.93% nutrient loss. The sum ratiow3:w6 as well as EPA: DHA (Docosahexaenoic) ratio in fried samples also varied significantly (p<0.5) lower than 0.668 and 0.20 for the average of either preservation methods and experts recommended ratio respectively. Further research has been recommended to ascertain the causative factor, since Mukene frying is being promoted in the Great lakes region as alternative method to sun-drying. In conclusion, regular consumers of fried Mukene do not benefit muchfrom the nutritional and health attributes of Omega 3 and 6.
  • Effects of cage fish culture on water quality and selected biological communities in northern Lake Victoria, Uganda

    Ndawula, L.M.; Kiggundu, V.; Magezi, G.; Naluwairo, J.; Pabire Ghandi, W.; Ocaya, H. (National Africultural Research Organisation, (NARO)Entebbe, Uganda, 2013)
    Growing of fish in cages is currently practiced in Uganda and was first introduced in northern Lake Victoria in 2010. An environment monitoring study was undertaken at Source of the Nile, a private cage fish farm, in Napoleon gulf, northern Lake Victoria. In-situ measurements of key environmental (temperature, dissolved oxygen, pH and conductivity) and biological (algae, zooplankton, macro-benthos) variables were made at three transects: Transect 1- the site with fish cages (WC); transect 2- upstream of the fish cages (USC-control) and Transect 3- downstream of the cages (DSC). Upstream and Downstream sites were located approximately 1.0 km from the fish cages. Environment parameters varied spatially and temporally but were generally within safe ranges for freshwater habitats. Higher concentrations of SRP (0.015-0.112 Mg/L) occurred at USC during February, September and at DSC in November; NO2-N (0.217- 0.042 mg/L) at USC and DSC in February and November; NH4-N (0.0054- 0.065 Mg/L) at WC and DSC in February,May and November. Algal bio-volumes were significantly higher at WC (F (2,780)=4.619; P=0.010).Zooplankton species numbers were consistently lower at WC with a significant difference compared to the control site (P=0.032). Macro-benthos abundance was consistently higher at the site with cages where mollusks and low-oxygen and pollution-tolerant chironomids were the dominant group. Higher algal biomass, concentration of low-oxygen/pollution-tolerant macro-benthos and depressed zooplankton diversity at WC suggested impacts from the fish cages on aquatic biota.
  • The past, present and projected scenarios in the Lake Albert and Albert Nile fisheries: implications for sustainable management

    Mbabazi, D.; Taabu-Munyaho, A.; Muhoozi, L.I.; Nakiyende, H.; Bassa, S.; Muhumuza, E.; Amiina, R.; Balirwa, J.S. (National Agricultural Research Organisation, 2012)
    Lake Albert is one of the largest lakes in Uganda that still supports a multi-species fishery which as a result of variable adult sizes of the species, causes management challenges especially in relation to gear mesh size enforcement. Prior to the 1980s, commercial species were 17 large sized fishes especially Citharinus citharinus, Distichodus niloticus and Lates spp. that were confimed to inshore habitats of the lake and were thus rapidly over fished. Frame and catch assessment surveys conducted in this study revealed a >80% dominance of small size fish species (Neobola bredoi and Brycinus nurse) and a 40 -60% decrease in the contribution of the large commercial species. Sustainability of small size fish species is uncertain due to seasonal fluctuations and low beach value. At about 150,000 tons of fish recorded from Lake Albert and Albert Nile, the beach value was estimated at 55.3 million USD. Despite the noted decline in catches of the large sized fishes their contribution was more than 50% of total beach value. Therefore, management measures should couple value addition for the small sized species and maintain effort regulation targeting recovery of the large previously important commercial species.
  • The past, present and projected scenarios in the Lake AIbert and Albert Nile fisheries: implications for sustainable management

    Mbabazi, D.; Taabu-Munyaho, A.; Muhoozi, L.I.; Nakiyende, H.; Bassa, S.; Muhumuza, E.; Amiina, R.; Balirwa, J.S. (National Africultural Research Organisation, (NARO)Entebbe, Uganda, 2012)
    Lake Albert is one of the largest lakes in Uganda that still supports a multi-species fishery which as a result of variable adult sizes of the species, causes management challenges especially in relation to gear mesh size enforcement. Prior to the 1980s, commercial species were 17 largesized fishes especially Citharinus citharinus, Distichodus niloticus and Lates spp. that were confmed to inshore habitats of the lake and were thus rapidly over fished. Frame and catch assessment surveys conducted in this study revealed a >80% dominance of small size fish species (Neobola bredoi and Brycinus nurse) and a 40 -60% decrease in the contribution of the large commercial species. Sustainability of small size fish species is uncertain due to seasonal fluctuations and low beach value. At about 150,000 tons of fish recorded from Lake Albert and Albert Nile, the beach value was estimated at 55.3 million USD. Despite the noted decline in catches of the large sized fishes their contribution was more than 50% of total beach value. Therefore, management measures should couple value addition for the small sized species and maintain effort regulation targeting recovery of the large previously important commercial species