Tamuka Nhiwatiwa
University of Zimbabwe, Biological Sciences, Faculty Member
- A freshwater scientistedit
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Research Interests: Management, Biology, Parasite, Fishery, Crustacean, and 5 moreTilapia, Intensity, Clarias gariepinus, Outbreak, and Oreochromis
Infestation of fish by the crustacean ectoparasite Lernaea cyprinacea Linnaeus, 1758 was investigated to establish the extent of infestation, potential effects of the parasite and its ecological adaptations. Fish samples were collected... more
Infestation of fish by the crustacean ectoparasite Lernaea cyprinacea Linnaeus, 1758 was investigated to establish the extent of infestation, potential effects of the parasite and its ecological adaptations. Fish samples were collected from impoundments in the Malilangwe Wildlife Reserve in the southeastern lowveld of Zimbabwe and these included the cichlids Oreochromis mossambicus, Oreochromis placidus and Tilapia rendalli, the cyprinids Labeo altivelis and Barbus paludinosus, the clariid Clarias gariepinus,> the centrarchid Micropterus salmoides and the characidHydrocynus vittatus. All the cichlids and one cyprinid (L. altivelis) were infested with L. cyprinacea. The two Oreochromis species exhibited prevalence as high as= 100% and mean intensity up to 149 parasites per fish. Lernaea cyprinacea exhibited an aggregated distribution in host populations and were attached mostly to the ventral and caudal regions of hosts, while the head was the least preferred attachment site. With a few exceptions, there was no significant correlation between parasite prevalence and intensity with host size, sex, condition factor, gonadosomatic index or fecundity.
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Research Interests: Earth Sciences, Biology, Ecology, Hydrobiology, Community, and 15 moreBiodiversity, Biological Sciences, Environmental Sciences, Flooding, Habitat, Drying, Floodplain, Species Diversity, Habitat fragmentation, Species Richness, Habitats, Connectivity, Predation Risk, Habitat Destruction, and Dry Season
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ABSTRACT Seasonal variations of plankton, expressed in terms of species composition and cell density in relation to selected physicochemical water parameters, were investigated in Malilangwe reservoir, Zimbabwe, between February and... more
ABSTRACT Seasonal variations of plankton, expressed in terms of species composition and cell density in relation to selected physicochemical water parameters, were investigated in Malilangwe reservoir, Zimbabwe, between February and October 2011. In total, 98 phytoplankton species (2 Dinophyta, 4 Euglenophyta, 14 Bacillariophyta, 50 Chlorophyta, 13 Desmids and 15 Cyanophyta), 66 zooplankton species (13 Cladocerans, 7 Calanoids/Cyclopoids, 46 Rotifers) and two others (Chaoborus sp. and Hydracarina) were recorded. Chlorophyta, Dinophyta and Cyanophyceae comprised the bulk of the phytoplankton, while Rotifera and Cladocera dominated the zooplankton community. A typical seasonal succession of plankton species occurred from February to October. Algal blooms were observed during May to July, dominated by Anabeana sp., Nostoc sp., Anabeana circinalis, Zygenema sp., Anabeana sporiodes, Ceratium hirudinella and Perinidium sp. Redundancy Analysis (RDA) showed that water level, conductivity, pH, dissolved oxygen, temperature, reactive phosphorus and macrophyte cover accounted for most of the distribution of the plankton species.
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Interactions between people and wild animals often result in negative impacts, and different views on the management of such interactions can lead to conflicts. Both intentional and unintentional negative human–wildlife interactions are... more
Interactions between people and wild animals often result in negative impacts, and different views on the management of such interactions can lead to conflicts. Both intentional and unintentional negative human–wildlife interactions are increasing problems in many places where people share space with wild animals. Here we focus on negative interactions between people and Nile crocodiles Crocodylus niloticus in and around Lake Kariba in Zimbabwe. In the study area, crocodile attacks on people occur frequently, leading to people being injured or killed, which in turn prompts retaliatory actions against crocodiles. However, despite the negative impact of such interactions on both people and crocodiles, little is known about the spatio-temporal patterns of crocodile attacks or environmental conditions under which attacks occur. We collected information about crocodile attacks on people that occurred during 2000–2020, including the date, time, season and location of attacks, the age of v...
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We construct a theoretical, deterministic mathematical model of the dynamics of Limnothrissa miodon with nutrients, phytoplankton, and zooplankton and investigate the effect of harvesting on the population density of Limnothrissa miodon... more
We construct a theoretical, deterministic mathematical model of the dynamics of Limnothrissa miodon with nutrients, phytoplankton, and zooplankton and investigate the effect of harvesting on the population density of Limnothrissa miodon in a lake. For the autonomous model, results from local stability analysis are in agreement with numerical simulations in that the coexistence equilibrium is locally stable, provided certain conditions are satisfied. The coexistence equilibrium is globally unstable if it is feasible. Numerical results show that a stable limit cycle exists for the nonautonomous model. Optimal control results show an optimal harvesting monthly effort of 15394 boat nights which corresponds to 505 fishing units, showing that there is overcapacity in Lake Kariba. A maximum sustainable annual catch of 34669 tonnes is obtained and simulation results show that Limnothrissa miodon abundance is more closely related to nutrient inflow than to harvesting.
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Although Cherax quadricarinatus is now established in Lake Kariba, there is a lack of information on the appropriate gear technology and bait for its exploitation for either management or commercial purposes. The effectiveness of three... more
Although Cherax quadricarinatus is now established in Lake Kariba, there is a lack of information on the appropriate gear technology and bait for its exploitation for either management or commercial purposes. The effectiveness of three trap designs and three bait types was investigated in order to identify the best means for harvesting C. quadricarinatus in Lake Kariba. The cylindrical and rectangular traps had higher and similar CPUE, which were significantly higher than those of the Opera house trap at all sites. Trap type did not influence sex ratio. Liver, sadza and fish heads were all similarly effective as bait. Either sadza-baited cylindrical or rectangular traps can be effectively employed to either harvest crayfish in order to maintain a low population, thereby mitigating potential adverse impacts, or for commercial purposes. This should be corroborated with monitoring and further research.
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The tourism industry sustains the economies of many nations across the globe through contributing to the Gross Domestic Products (GDP); creation of employment and infrastructure development. However, its sustainability is vulnerable to... more
The tourism industry sustains the economies of many nations across the globe through contributing to the Gross Domestic Products (GDP); creation of employment and infrastructure development. However, its sustainability is vulnerable to various temporal and spatial environmental, socio-economic and political events. In the Zimbabwe case, the politico-economic crises of the 2000s and the COVID-19 pandemic have variedly impacted on the prevalence of tourism with the actors (such as employees, tourists and recreational facility owners) involved in this industry having been seriously impacted. Using the precarity conceptual framework, this article critically analyses the impact of the politico-economic crises induced by the Fast Track Land Reform Programme of the early 2000s and the COVID-19 pandemic on the actors involved in tourism. Information regarding the impact of the political crises and COVID-19 pandemic on tourism in Kariba town is missing in the literature, yet Kariba is one of...
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Temporary freshwater pools or pans are known for their nature value and socio-economic importance especially in arid and semi-arid regions, but it is still poorly known how they develop in a natural setting. The ecologically valuable... more
Temporary freshwater pools or pans are known for their nature value and socio-economic importance especially in arid and semi-arid regions, but it is still poorly known how they develop in a natural setting. The ecologically valuable temporary freshwater pans of the Save Valley Conservancy in Zimbabwe, are studied in order to gain insights into their formation. Field observations of 17 existing pans and in situ measurements at one possible site of pan formation were done. It was observed that in most cases trees were bordering existing pans with Diospyros mespiliformis being present at eight locations and Colophospermum mopane at five. These two species were co-existing at two locations which had also dead trees present. On the basis of these observations, a suspected developing pan was followed up using hydrological field observations to understand processes that are important in pan formation. In situ infiltration tests as well as penetrometer tests, before and after a rainfall ev...
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Man-made reservoirs are constructed to meet certain purposes and Lake Kariba, Zimbabwe, was designed for hydroelectric power generation. However, it has developed other multiple uses, and the growth of fisheries on the lake has had a... more
Man-made reservoirs are constructed to meet certain purposes and Lake Kariba, Zimbabwe, was designed for hydroelectric power generation. However, it has developed other multiple uses, and the growth of fisheries on the lake has had a significant impact on the livelihoods of local communities. The declaration of Covid-19 as a pandemic in Zimbabwe in March 2020 was quickly followed by the imposition of national lockdowns with varying levels of severity up to the present day. This was done to curtail the spread of the disease, meanwhile enhancing the nation’s capacity in terms of acquiring testing kits, constructing more admission and quarantine centres as well as educating the people about ways to keep safe. In response to the calls by the government to monitor the movement of people and compliance of the lockdown rules, the Zimbabwe National Parks and Wildlife Management Authority (ZNPWMA), the governing body of the Lake Kariba fisheries, imposed rules that have significantly impacte...
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The aim of this study was to determine the effect of greenhouse culture conditions on water quality variables that are important for tilapia aquaculture. Six experimental ponds, three in open atmosphere and three under greenhouses were... more
The aim of this study was to determine the effect of greenhouse culture conditions on water quality variables that are important for tilapia aquaculture. Six experimental ponds, three in open atmosphere and three under greenhouses were set up. Each pond was further subdivided by hapas to make 12 experimental units of which half were stocked with Oreochromis niloticus and the other Oreochromis macrochir. Water was sampled fortnightly from each pond for chemical and physical quality assessment. Water temperature, conductivity, turbidity, total dissolved solids, dissolved oxygen and pH, were determined in-situ over a period of 24 hours. The following chemical variables were also analysed: biological oxygen demand, chemical oxygen demand, alkalinity, chlorides, chlorophyll a, nitrates, total phosphorus, reactive phosphorus, total suspended solids and ammonia. Water temperatures, chlorophyll a and reactive phosphorus concentrations were significantly higher in the greenhouse ponds than i...
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Age and growth of Nile tilapia, Oreochromis niloticus (L.) were determined using sample from Lake Chivero (Zimbabwe) caught from 2009 to 2011. The length-weight relationship for all individuals was W = 0.015 TL 0.304 . The sex ratio of... more
Age and growth of Nile tilapia, Oreochromis niloticus (L.) were determined using sample from Lake Chivero (Zimbabwe) caught from 2009 to 2011. The length-weight relationship for all individuals was W = 0.015 TL 0.304 . The sex ratio of female to male was 1:1.27. Fish age derived from both length frequencies and scales showed no significant difference (p > 0.05, Paired T-test). The length frequency age data were used to estimate the growth parameters of the von Bertalanffy equation. The mean values from 2009 to 2011 were: L∞ 39.41, K = 0.41, (o) = 2.798, Lm 50 = 23.33 cm, Lc 50 = 22.60 cm, Z = 1.84 year -1 , M= 0.81 year -1 , F = 1.04 year -1 and E = 0.58 year-1. Growth, mortality and exploitation parameters L∞, K, (o) and Z were compared from year to year and results showed the fishery is over-exploited. Fish below age/length at first maturity form the bulk of the fish harvested by the fishery. Increasing length at first capture could increase yield per recruit and also protect s...
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The stomach contents of tigerfish Hydrocynus vittatus, caught in an angling competition on Lake Kariba, were examined to determine the extent to which they feed on the invasive crayfish Cherax quadricarinatus. The stomach contents of 281... more
The stomach contents of tigerfish Hydrocynus vittatus, caught in an angling competition on Lake Kariba, were examined to determine the extent to which they feed on the invasive crayfish Cherax quadricarinatus. The stomach contents of 281 tigerfish caught during three tournaments (2013, 2014 and 2015) were examined and grouped into six main categories. The proportion of empty stomachs ranged from 4.6 to 13.9% in males and from 11.9 to 29.1% in females. The main food items according to the frequency of occurrence were fish (Limnothrissa miodon (69.0 ± 13.0%) fish remains (bones and scales; 33.0 ± 22.0%), Cichlidae (26.8 ± 2.10%) and Mormyridae (0.5 ± 0.9%) and invertebrates, such as crayfish (24.9 ± 4.6%) and insects (5.2 ± 2.1%). This tournament has been useful in confirming changes in tigerfish diet following the introduction and establishment of non-native species, such as Limnothrissa miodon and, more recently, the crayfish, C. quadricarinatus.
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Raw water quality deterioration has affected capabilities of Conventional Water Treatment Processes (CWTP) in many countries. CWTP used at Morton Jaffray Water Treatment Works (MJWTW) in Harare have proven ineffective due to pollution.... more
Raw water quality deterioration has affected capabilities of Conventional Water Treatment Processes (CWTP) in many countries. CWTP used at Morton Jaffray Water Treatment Works (MJWTW) in Harare have proven ineffective due to pollution. The study investigated the use of chlorine dioxide (ClO2) as an alternative pre-treatment chemical. Its effectiveness was compared to that of calcium hypochlorite (Ca(CIO)2) used at MJWTW. Grab raw water samples from MJWTW were collected between January and March 2020 and pre-treated with ClO2 and Ca(CIO)2 followed by jar tests with alum to determine pre-treatment effectiveness. Parameters analyzed included electrical conductivity (EC), total dissolved solids (TDS), total solids (TS), turbidity, chemical oxygen demand (COD), pH and total algae counts (TAC). The raw water had mean TDS (264 mg/L), TS (440 mg/L), turbidity (7.1 NTU), COD (85 mg/L), pH (7.9) and TAC (28.4 × 106 cells/mL). The optimum alum dosage without pre-oxidation was 80 mg/L. Pre-oxid...
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The stratification of a lentic water system is an important factor regulating its biotic activities and processes. The present study investigated changes in temperature and oxygen stratification regimes in Mazvikadei Reservoir 27 years... more
The stratification of a lentic water system is an important factor regulating its biotic activities and processes. The present study investigated changes in temperature and oxygen stratification regimes in Mazvikadei Reservoir 27 years after the first study was conducted during its filling phase. The FLake‐Global model was also tested as a predictive tool for the first time to analyse annual limnological trends in a subtropical reservoir. The lake‐modelling tool FLake‐Global enables an instantaneous estimation of the seasonal cycle of temperature and mixing conditions in shallow freshwater lakes around the world. The results of the present study illustrate that the reservoir was weakly stratified, with the overall thermal stratification patterns somewhat similar to those recorded during the filling phase (1992). The oxygen stratification patterns observed in the present study correspond well to those of thermal stratification. The depth‐integrated oxygen profiles for both the deep a...
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Impact of Lernaea cyprinacea Linnaeus 1758 (Crustacea : Copepoda) almost a decade after an initial parasitic outbreak in fish of Malilangwe Reservoir, Zimbabwe Impact de la Lernaea cyprinacea (Crustacea : Copepoda) près d’une décennie après une première épidémie parasitaire chez les poissons du r...more
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Global warming is a serious world problem where earth’s temperature has been reported to increase over the years; the aquatic ecosystems are also not the exceptions. But, the effects of this phenomenon on the aquatic ecosystems are not... more
Global warming is a serious world problem where earth’s temperature has been reported to increase over the years; the aquatic ecosystems are also not the exceptions. But, the effects of this phenomenon on the aquatic ecosystems are not well understood. This study aims to understand the influence of surface temperature on the population density of Limnothrissa miodon in Lake Kariba. We constructed a mathematical model on the population dynamics of Limnothrissa miodon with nutrients, phytoplankton, zooplankton, and Hydrocynus vittatus. Lake surface water temperature was modelled by a cosine function, and the parameters were estimated from data fitting. Numerical simulations were used to determine the stability of the nonautonomous model. Numerical simulation results of the nonautonomous model showed a stable periodic orbit for varying initial conditions, and therefore, instability. Numerical techniques were used to investigate the influence of surface water temperature on Limnothrissa...
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In this paper, we construct and analyze a theoretical, deterministic 5 D mathematical model of Limnothrissa miodon with nutrients, phytoplankton, zooplankton, and Hydrocynus vittatus predation. Local stability analysis results agree with... more
In this paper, we construct and analyze a theoretical, deterministic 5 D mathematical model of Limnothrissa miodon with nutrients, phytoplankton, zooplankton, and Hydrocynus vittatus predation. Local stability analysis results agree with the numerical simulations in that the coexistence equilibrium is locally stable provided that certain conditions are satisfied. The coexistence equilibrium is globally stable if certain conditions are met. Existence, stability, and direction of Hopf bifurcations are derived for some parameters. Bifurcation analysis shows that the model undergoes Hopf bifurcation at the coexistence point for the zooplankton growth rate with periodic doubling leading to chaos.
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This study aimed at characterising Oreochromis niloticus fish species of Lake Kariba and was premised on the hypothesis that there are different types of O. niloticus fish species in Lake Kariba. Oreochromis niloticus fish specimens... more
This study aimed at characterising Oreochromis niloticus fish species of Lake Kariba and was premised on the hypothesis that there are different types of O. niloticus fish species in Lake Kariba. Oreochromis niloticus fish specimens (n = 409) were collected from both culture fisheries (Yalelo fishery, Fwanyanga fishery and Choombwe fishery) and capture fisheries (Siavonga and Sinazongwe) based at Lake Kariba from April to November 2020. All the collected fish samples were used for phenotypic characterisation, while 98 were used for genetic characterisation. A total of 23 morphometric measurements and seven meristic counts were used to generate morphometric data which were analysed using multivariate analysis. In order to delineate the sampled specimens, dendrograms were generated. Further, microsatellite data were generated from 98 samples using a panel of five microsatellite markers and analysed using microsatellite toolkit, GenAIEx, Fstat and LIAN software. Meristic results of cul...
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The limnology of Mazvikadei Reservoir, northern Zimbabwe, was investigated in 2015 to determine whether it had changed since filling in 1990. The reservoir is characterised by low algal biomass, low nutrients (i.e. N and P) and high water... more
The limnology of Mazvikadei Reservoir, northern Zimbabwe, was investigated in 2015 to determine whether it had changed since filling in 1990. The reservoir is characterised by low algal biomass, low nutrients (i.e. N and P) and high water clarity/transparency. Fifty-four species of phytoplankton were recorded, comprising Bacillariophyta, Chlorophyta, Cyanophyta, Desmids, Dinophyta and Euglenophyta. Chlorophyta numerically dominated in the hot dry season, whereas Bacillariophyta, Desmids, Dinophyta and Euglenophyta dominated in the cool dry season. Species richness was highest at the onset of the cool dry season, in response to high nutrient concentrations. Phytoplankton abundance and composition were significantly correlated with temperature, nitrates and total nitrogen. Nineteen zooplankton species were recorded, including Copepoda, Cladocera and Rotifera. Overall, Cladocera were numerically dominant and became most abundant during the cool dry season. Rotifers and copepods dominated during the hot dry season. The zooplankton abundance was correlated with reactive phosphorus and phytoplankton abundance. The trophic state of Mazvikadei Reservoir seems to have stabilised and to have assumed the physico-chemical characteristics and plankton community typical of an oligotrophic lake.
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Human–wildlife conflicts (HWCs) are on the increase due to shrinking space that results in increased competition for land, water, and other natural resources between humans and wildlife. Investigating the occurrence of HWCs is important... more
Human–wildlife conflicts (HWCs) are on the increase due to shrinking space that results in increased competition for land, water, and other natural resources between humans and wildlife. Investigating the occurrence of HWCs is important in that the results can be used to formulate better management policies and strategies. In this paper, we describe the nature of HWCs emerging between humans and the Nile crocodile (Crocodylus niloticus) and between humans and the African hippopotamus (Hippopotamus amphibius; hippo) on Lake Kariba, Zimbabwe. Lake Kariba is the second largest manmade lake by volume in the world. Conflicts involving humans and these species are readily noticeable and played out around water bodies, which are sources of daily human sustenance and important habitats for aquatic wildlife. We used a mixed-methods approach to gather data on these conflicts, including questionnaires, face-to-face interviews, focus group discussions, and participant observation. The research ...
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The plankton assemblages of Tugwi-Mukosi reservoir in south-eastern Zimbabwe were assessed seven months after impoundment to form a baseline for future monitoring and tracking of changes linked to the reservoir’s ontogenetic development... more
The plankton assemblages of Tugwi-Mukosi reservoir in south-eastern Zimbabwe were assessed seven months after impoundment to form a baseline for future monitoring and tracking of changes linked to the reservoir’s ontogenetic development processes. While cyanobacteria were the dominant group at all sites (50−70%), relative abundances of Bacillariophyceae and Chlorophyceae was considerable. The most abundant phytoplankton species were Microcystis aeruginosa and Aulacoseira granulata, whose abundances ranged from 3 200−28 800 ind. l−1 and 1 640−3 146 ind. l−1, respectively. Phytoplankton species richness in the reservoir ranged from 9 to 20, with the highest species richness in the north-eastern region of the reservoir. Zooplankton density was <1 ind. l−1 and after seven months since impoundment, the zooplankton community had not fully established. Twenty zooplankton species comprising of Rotifera, Copepoda and Cladocera were recorded. Cladocera, mainly Diaphanosoma excisum and Ceriodaphnia cornuta, were the most abundant followed by copepods, mainly Thermoclops sp. and Eodiaptomus japonicas. The dominance of Microcystis aeruginosa presents potential future challenges to water quality management, because increased nutrient loading can favour it, resulting in similar challenges being experienced in Lake Chivero. The establishment of an Integrated Lake Basin Management is strongly recommended to avert this.