Browsing by Author "Waidbacher, Herwig"

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    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, Harald
    Nile 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.
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    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, Herwig
    Approximately 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.
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    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, Herwig
    Most 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.
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    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, Herwig
    The 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.
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    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, Harald
    The 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.