Browsing by Author "Akoll, Peter"
Now showing 1 - 12 of 12
Results Per Page
Sort Options
Item Anthropogenic impacts on the contextual morphological diversification and adaptation of Nile tilapia (Oreochromis niloticus, L. 1758) in East Africa(Environmental Biology of Fishes, 2018) Dias Tibihika, Papius; Waidbacher, Herwig; Masembe, Charles; Curto, Manuel; Sabatino, Stephen; Alemayehu, Esayas; Meulenbroek, Paul; Akoll, Peter; Meimberg, HaraldNile tilapia occurs naturally in East Africa where it’s an economically important species. Many of the natural populations of Nile tilapia have been affected by anthropogenic activities including translocations, associated with programmes aimed at enhancing capture fisheries and aquaculture productivity. Using geometric morphometric analyses, we tested the hypothesis that such anthropogenic activities have augmented admixture among natural populations of Nile tilapia and influenced the geographical distribution of morphological variation within the species. Our expectation was that Nile tilapia shape divergent might be consistent with reportedly anthropogenic activities in nonnative environments. To test this hypothesis, we analyzed the shapes of 490 individuals from thirteen populations; three farms, six natives and four nonnative natural populations. Our analysis revealed that the most pronounced shape diversification was observed in seven populations; three nonnatives (Victoria, Kyoga and Sindi farm) and four natives (Albert, River Nile, George and Turkana). The features responsible for the observed morphotypes were mainly related to the orientation of the anterior region of the fish and may be due to diversifying selection in response to new environmental pressures (for nonnative populations), admixture or drift. Shape change in the nonnative high-altitude populations was unexpectedly conserved, suggesting recent introductions which may have not resulted in admixture or there was strong selection against change in the traits measured. On the other hand, the recorded morphotypic clusters explained the possible genetic link to their putative ancestral home. Our results were partially consistent with our prediction that the nonnative populations exhibited divergent morphotypes. We recommend further investigations with molecular genetics for followup of these findings.Item The Contribution of Fish to Food and Nutrition Security in Eastern Africa: Emerging Trends and Future Outlooks(Sustainability, 2019) Obiero, Kevin; Meulenbroek, Paul; Drexler, Silke; Dagne, Adamneh; Akoll, Peter; Odong, Robinson; Kaunda-Arara, Boaz; Waidbacher, HerwigApproximately 200 million people in Africa derive high-quality and low-cost proteins from fish. However, the consumption of fish is not fully exploited to combat the “triple burden” of malnutrition—obesity, undernutrition, and micronutrient deficiencies which are the leading causes of poor health in the region. There is still limited knowledge on quantitative information to guide policy makers in developing evidence-based actions that can improve the availability of and access to nutritious food for healthy and sustained diets among children and care givers. In this paper, we review the available literature with the aim of assessing and quantifying the extent to which fish contributes towards fighting food and nutrition insecurity in the Eastern Africa subregion. Key results reveal the region is characterized by fish supply deficits, and hence, low levels of fish consumed per person. Nonetheless, the increase in fish imports, and the growing supply of fish from aquaculture are likely to improve the per-capita fish intake. Fish trade is generally bidirectional, with exports exceeding imports in value terms, while significant challenges still hinder domestic and intra-regional fish trade. The Eastern Africa region is projected to realize increased fish consumption from 4.80 kg in 2013 to 5.49 kg by 2022. Rising population growth and income levels imply that the region will need 2.49 million tonnes of fish to fill the demand–supply gaps. We recommend that food security and nutritional programmes should recognize the potential of fish in providing essential micronutrients from the aspects of improved dietary quality, nutritional status, and general wellbeing of the region’s fast growing population.Item Dietary inclusion of pine pollen alters sex ratio and promotes growth of Nile tilapia (Oreochromis niloticus, L. 1758)(Aquaculture Reports, 2022) Abaho, Ivan; Akoll, Peter; Jones, Clifford L.W.; Masembe, CharlesThe potential of pine pollen (PP) to masculinize sexually undifferentiated Nile tilapia was evaluated by feeding graded levels of PP (0.08–3.20 g kg-1 basal diet) to triplicate groups of three-day-old Nile tilapia for 28 days. Masculinization and associated differences in growth were compared to fish individuals fed the same basal diet with no PP (CT; negative control) and with 0.06 g 17α-methyltestosterone (MT) kg-1 basal diet (positive control). Both PP and MT treatments significantly skewed the expected 50:50 (male: female) ratio towards more male individuals. Notably, MT and 1.28 g PP kg-1 of diet produced a significantly high proportion of males (89.2 ± 2.2% and 80.0 ± 2.9% respectively), compared to 50.8 ± 2.2% in the CT treatment (P < 0.001). Except for 0.08 g PP kg-1 of diet, the final body weight and specific growth rate of individuals fed PP and MT-supplemented feeds were significantly higher than fish from the CT group. Although 1.28 g PP kg-1 diet produced the highest masculinization, the fish fed 3.20 g PP kg-1 diet had the highest final weight (14.73 ± 0.54 g), suggesting the presence of growth enhancers in PP. Similarly, a superior feed conversion ratio was recorded in both PP and MTtreated groups compared to the CT treatment (P = 0.024). However, the condition factor and survival rate of fish in all groups did not differ significantly. Overall, 1.28 g PP kg-1 diet was potent in sex inversion and promoted the growth of Nile tilapia, making PP a promising alternative to MT in the production of all-male stock.Item Effects of aerated and non-aerated biofilters on effluent water treatment from a small-scale recirculating aquaculture system for Nile tilapia (Oreochromis niloticus L.)(Journal of Land Management, Food and Environment, 2019) Gichana, Zipporah; Liti, David; Drexler, Silke-Silvia; Zollitsch, Werner; Meulenbroek, Paul; Wakibia, Joseph; Ogello, Erick; Akoll, Peter; Waidbacher, HerwigMost recirculation aquaculture systems (RAS) use aerated biofilters to maintain suitable water quality for fish production. However, application of non-aerated biofilters may provide opportunities to lower aeration costs, water usage and concentration of all nitrogenous wastes in the effluent water. Our study aimed at comparing the biofiltration performance characteristics of two biofilters: a conventional aerated biofilter and a non-aerated biofilter receiving the same effluent water from a small-scale RAS. The two biofilters were evaluated in triplicate and tested concurrently for seven months. Water quality parameters were monitored at the biofilter inlets and outlets and in the fish tanks. At the beginning of the experiment, the concentration of ammonia at the two biofilter outlets were not significantly different. However, the concentrations decreased with time reaching mean values of 1.33 ± 0.02 mg L-1 and 1.23 ± 0.21 mg L-1 N-NH4 in the aerated and non-aerated biofilters, respectively. Whereas phosphorus and nitrate levels were significantly high in the aerated biofilter. There was no significant difference in the growth of fish between the aerated and non-aerated biofilters. The results suggest that non-aerated biofilters can be as effective as aerated biofilters in maintaining suitable water quality for O. niloticus production.Item Genetic diversity and population structure of selected lacustrine and riverine populations of African catfish, Clarias gariepinus (Burchell, 1822), in Kenya(Journal of Applied Ichthyology, 2021) Alal, George W.; Barasa, James E.; Chemoiwa, Emily J.; Kaunda-Arara, Boaz; Akoll, Peter; Masembe, CharlesDetermining the genetic characteristics of natural fish stocks is useful for conservation and aquaculture programs. For African catfish, Clarias gariepinus, genetic characterization could help identify populations suitable as brood stock for culture, and those in need of conservation. This study determined the genetic diversity, population structure, and demographic history of C. gariepinus from Lakes Victoria (LV), Kenyatta (LKE), Kamnarok (LKA), and Rivers Nyando (NR), Tana (TR) and Sosiani (SR) in Kenya. Using 128 DNA sequences of D-loop control region, 34 haplotypes were recovered, of which 79.4% were singletons. Only 7 haplotypes were shared between sites, implying little gene flow between sites. Number of haplotypes was highest in LKE and NR populations and lowest in SR. Haplotype diversity was highest in LV, and lowest in SR, while, nucleotide diversity was highest in LKA and lowest in LV. Phylogenetic analyses revealed five clusters: Lakes Victoria, Kamnarok and Kenyatta, and Rivers Tana and Nyando, from both maximum likelihood tree and minimum spanning network. This, together with significant FST values among the sites imply population differentiation. Mismatch distributions were multi-modal in LKA, LKE, NR and TR, signifying demographic equilibria. Neutrality tests Tajima`s D values for the sampled populations were negative and significantly different, suggesting stable populations. These results show the existence of genetically distinct populations of C. gariepinus that require spatially explicit management actions such as reducing fishing pressure, pollution, minimizing habitat destruction and fragmentation for sustainable utilisation of stocks.Item Growth and Nutrient Removal Efficiency of Sweet Wormwood (Artemisia annua) in a Recirculating Aquaculture System for Nile Tilapia (Oreochromis niloticus)(Water, 2019) Gichana, Zipporah; Meulenbroek, Paul; Ogello, Erick; Drexler, Silke; Zollitsch, Werner; Liti, David; Akoll, Peter; Waidbacher, HerwigThe maintenance of optimal water quality for fish production is one of the major challenges in aquaculture. Aquaponic systems can improve the quality of water for fish by removing the undesirable wastes and in turn produce a second marketable crop. However, there is no information on the growth and nutrient removal capability of Artemisia annua in aquaponic systems. This study evaluated the effeect of plant density on water quality, the growth of A. annua and Oreochromis niloticus in a small scale aquaponic system in Kenya. The aquaponic system consisted of three treatments representing different plant densities (D1: 48 plants/m2, D2: 24 plants/m2 and D3:0 plants/m2). The high plant density system contributed significantly (p < 0.05) to the removal of all nutrients. The removal efficiency of ammonia was significantly higher in D1 (64.1 14.7%) than in D2 (44.5 6.8%) and D3 (38.0 12.1%). Nitrates and nitrites were inconsistent, whereas phosphorus increased gradually in all treatments. The productivity of plants was higher in D1 than D2. Fish growth rates were significantly higher in D1 (0.35 0.03 g/d) and D2 (0.32 0.02 g/d) than in D3 (0.22 0.04 g/d). The results show that A. annua can be cultivated in aquaponic systems due to its nitrogen removal capabilities.Item Infection patterns of Nile tilapia (Oreochromis niloticus L.) by two helminth species with contrasting life styles(Parasitology research, 2012) Akoll, Peter; Konecny, Robert; Mwanja, Wilson W.; Schiemer, FritzThe larval stages of Bolbophorus sp. (digenean) and Amirthalingamia macracantha (cestode) are frequently reported in Oreochromis niloticus in Uganda. Little, however, is known about their infection patterns. This study examined the influence of habitat type, host size, and sex and weather patterns on the parasite populations in Uganda. A total of 650 fish were collected between January and November 2008 from a reservoir, cages, fishponds and a stream. The prevalence and intensity of A. macracantha and the prevalence of Bolbophorus sp. differed across the water bodies reflecting the effect of habitat characteristics on parasite transmission. Host sex did not significantly influence the infection patterns, although female fish were slightly more parasitized than male and sexually undifferentiated individuals. The fish size was positively correlated with helminth infections demonstrating accumulation and prolonged exposure of larger (older) fish to the parasites. The metacercariae population did not vary significantly across months, while monthly A. macracantha infection fluctuated markedly. With regard to rain seasons, higher prevalence and intensity of A. macracantha were recorded in wet season. For Bolbophorus sp., only the prevalence varied with seasons, with higher prevalence recorded in the dry season than in wet season. Generally, Bolbophorus sp. responded weakly to changes in water body, host sex and size and weather patterns. Rainfall appears to be an essential cue for coracidia hatching.Item Molecular genetic diversity and differentiation of Nile tilapia (Oreochromis niloticus, L. 1758) in East African natural and stocked populations(BMC Evolutionary Biology, 2020) Tibihika, Papius Dias; Curto, Manuel; Alemayehu, Esayas; Waidbacher, Herwig; Masembe, Charles; Akoll, Peter; Meimberg, HaraldThe need for enhancing the productivity of fisheries in Africa triggered the introduction of non-native fish, causing dramatic changes to local species. In East Africa, the extensive translocation of Nile tilapia (Oreochromis niloticus) is one of the major factors in this respect. Using 40 microsatellite loci with SSR-GBS techniques, we amplified a total of 664 individuals to investigate the genetic structure of O. niloticus from East Africa in comparison to Ethiopian and Burkina Faso populations. Results: All three African regions were characterized by independent gene-pools, however, the Ethiopian population from Lake Tana was genetically more divergent (Fst = 2.1) than expected suggesting that it might be a different sub-species. In East Africa, the genetic structure was congruent with both geographical location and anthropogenic activities (Isolation By Distance for East Africa, R2 = 0.67 and Uganda, R2 = 0.24). O. niloticus from Lake Turkana (Kenya) was isolated, while in Uganda, despite populations being rather similar to each other, two main natural catchments were able to be defined. We show that these two groups contributed to the gene-pool of different non-native populations. Moreover, admixture and possible hybridization with other tilapiine species may have contributed to the genetic divergence found in some populations such as Lake Victoria. We detected other factors that might be affecting Nile tilapia genetic variation. For example, most of the populations have gone through a reduction in genetic diversity, which can be a consequence of bottleneck (G-W, < 0.5) caused by overfishing, genetic erosion due to fragmentation or founder effect resulting from stocking activities. Conclusions: The anthropogenic activities particularly in the East African O. niloticus translocations, promoted artificial admixture among Nile Tilapia populations. Translocations may also have triggered hybridization with the native congenerics, which needs to be further studied. These events may contribute to outbreeding depression and hence compromising the sustainability of the species in the region.Item Parasite fauna of farmed Nile tilapia (Oreochromis niloticus) and African catfish (Clarias gariepinus) in Uganda(Parasitology research, 2012) Akoll, Peter; Konecny, Robert; Mwanja, Wilson W.; Nattabi, Juliet K.; Agoe, Catherine; Schiemer, FritzAn intensive parasite survey was conducted in 2008 to better understand the parasite fauna occurrence, distribution and diversity in the commercial aquaculture fish species in Uganda. A total of 265 fish collected from hatcheries and grow-out systems were examined for parasites using routine parasitological techniques. The survey yielded 17 parasite species: 11 from Oreochromis niloticus and ten from Clarias gariepinus. Four parasites—Amirthalingamia macracantha, Monobothrioides sp., Zoogonoides sp. and a member of the family Amphilinidae—were recorded for the first time in the country. The parasite diversity was similar between hosts; however, O. niloticus was dominated by free-living stage-transmitted parasites in lower numbers, whereas both trophically and free-living stage-transmitted parasites were equally represented in C. gariepinus in relatively high intensities. The patterns in parasite numbers and composition in the two hosts reflect differences in fish habitat use and diet. A shift in parasite composition from monoxenous species-dominated communities in small-sized fish to heteroxenous in large fishes was recorded in both hosts. This was linked to ontogenetic feeding changes and prolonged exposure to parasites. Polyculture systems showed no effect on parasite intensity and composition. The gills were highly parasitized, mainly by protozoans and monogeneans. Generally, the occurrence and diversity of parasites in these fish species highlight the likelihood of disease outbreak in the proposed intensive aquaculture systems. This calls for raising awareness in fish health management among potential farmers, service providers and researchers.Item Risk assessment of parasitic helminths on cultured Nile tilapia (Oreochromis niloticus, L.)(Aquaculture, 2012) Akoll, Peter; Konecny, Robert; Mwanja, Wilson W.; Schiemer, FritzDisease outbreaks constrain aquaculture development. Knowledge on the potential risks of pathogens to farmed fish can help in designing management strategies for increased aquaculture productivity and sustainability. This study compares the helminth infections in reservoirs and therein operated cages as well as earthen fish ponds and the feeding stream in order to assess the significance of life cycle style and water sources in parasite transmission. In addition field experiments were setup to determine loading time and transmission rate. From 650 fish examined, 8 helminth species were recorded (3 from caged- and all 8 from pond-raised fish). The parasite community was dominated by trophically-transmitted species in both culture systems indicating the importance of trophic pathway in helminth transmission. The occurrence of trophically-transmitted helminths in caged-fish was positively related to their prevalence in reservoir-dwelling hosts indicating the importance of water supply in spread of helminths. The prevalence in pond-raised fish was higher than in stream-dwelling ones suggesting the presence of local sources of infective stages within ponds. Risk assessment revealed that monogeneans are high-risk parasites while heteroxenous helminths pose low to negligible threats to farmed fish. Although, cages appeared safer to heteroxenous parasites than ponds, their location in the water body, especially the distance from shores and depth is critical.Item The use of plant extracts to control tilapia reproduction: Current status and future perspectives(Journal of The World Aquaculture Society, 2022) Abaho, Ivan; Masembe, Charles; Akoll, Peter; Jones, Clifford L. W.Control of prolific reproduction is vital for a profitable tilapia aquaculture enterprise. All-male tilapia culture is a popular method used to control prolific breeding, because the male individuals grow faster than female and mixed-sex populations. Presently, most farmers use 17α-methyl testosterone (MT) to produce all-male tilapia individuals, although synthetic hormones are linked to human health and environmental risks. Recently, considerable attention has focused on plant-based products as alternatives to MT, because they are affordable, safe, and eco-friendly. Despite the growing interest in using plant extracts to prevent frequent spawning in tilapia production, the available information is not collated to standardize application guidelines. Accordingly, this review article consolidates existing knowledge on the use of plant extracts to control prolific breeding in tilapia culture systems. In addition, limitations to commercial application of the extracts are identified. To date, seed, root, and leaf extracts of 20 plant species, most notably, Tribulus terrestris, Mucuna pruriens, and Carica papaya, exhibit potential for controlling unwanted breeding in tilapia production systems. The extracts are mainly administered orally, incorporated in fish feeds. Saponins and flavanoids are the main bioactive compounds in the phytoextracts, which induce sex inversion and fertility impairment in tilapia. The commercialization of plant extracts is, however, hampered by lack of standardized information on extract preparation, optimal dosages, and mechanism of action. Thus, future studies should address these technical limitations and highlight economic incentives for commercial use of plant extracts in tilapia aquaculture.Item Veterinary and public health aspects in tilapia (Oreochromis niloticus niloticus) aquaculture in Kenya, Uganda and Ethiopia(Ittiopatologia, 2009) Florio, Daniela; Gustinelli, Andrea; Caffara, Monica; Turci, Francesco; Quaglio, Francesco; Konecny, Robert; Nikowitz, Tanja; Wathuta, Euty M.; Magana, Adiel; Otachi, Elick O.; Matolla, Geraldine K.; Warugu, Hellen W.; Liti, David; Mbaluka, Raphael; Thiga, Benson; Munguti, Jonathan; Akoll, Peter; Mwanja, Wilson; Asaminew, Kassahun; Tadesse, Zenebe; Letizia Fioravanti, MariaThe European INCO-DEV BOMOSA Project (Integrating BOMOSA cage fish farming systems in reservoirs, ponds and temporary water bodies in Eastern Africa) intends to establish small scale fish farming in marginal water bodies in Kenya, Uganda and Ethiopia, creating rural aquaculture networks with the aim to economically integrate aquaculture with agriculture. In order to study veterinary and public health aspects in Bomosa fish farming systems, a parasitological survey on wild and cultured tilapias (Oreochromis niloticus niloticus) has been carried out from March 2007 to October 2008. A total of 982 tilapias - 685 from Kenya, 222 from Uganda and 75 from Ethiopia - were sampled and subjected to complete parasitological examination. During the survey, fish from different environments (258 from open water reservoirs, 445 from ponds and 279 from BOMOSA cages) were sampled in order to evaluate the factors which could influence the parasite diffusion and outbreak of diseases. Quantitative data, such as prevalence, intensity and abundance, and qualitative data are presented together with the main abiotic and biotic risk factors identified as relevant for veterinary and public health aspects in tilapia aquaculture.