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The aim of our study was to investigate macroinvertebrate communities so as to understand factors and processes structuring macroinvertebrate communities in a small reservoir, Malilangwe reservoir over seven months (April to October). Sampling was performed by active sweep netting and searching soil sediments. Water temperature, conductivity, dissolved oxygen, pH, ammonia, nitrogen, phosphorus, chemical oxygen demand and macrophyte cover were determined. In total, forty-two macroinvertebrate families belonging to 10 orders were identified amongst 13 macrophyte species and sediments. Thiaridae and Physidae (Mollusca) were the dominant and most abundant taxa (57.71%) and there were followed by the Hemiptera (27.31%). High indices for sites 1 to 3 for the Simpsons index, the Shannon-Weaver index and evenness were recorded, while low indices were observed for sites 4 to 5, with significant differences being observed among the study site using the Kruskal-Wallis ANOVA test (p

An assessment was carried out on the impact of Lernaea cyprinacea on fish populations ten years after its first outbreak in the Malilangwe reservoir, and Lernaea cyprinacea is currently showing no sign of declining in the reservoir. Eight fish species were examined for ectoparasite prevalence and intensity. The possible relationship between L. cyprinacea infestation and environmental factors were investigated. Two parasite species, L. cyprinacea in Oreochromis mossambiccus, Oreochromis placidus, Oreochromis macrochir, Labeo altivelis and Tilapia rendalli and trematode cysts (Clinostomoides brieni) in Clarias gariepinus were found. Lernaea cyprinacea prevalence was 100% amongst all cichlids but varied for L. altivelis. Parasite intensity increased during the cool, dry season (May to July), with the greatest mean intensity being observed amongst the cichlids. There was a significant relationship between parasite intensity and environmental factors; dissolved oxygen (p

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The physico-chemical limnology and trophic status of the Tugwi-Mukosi reservoir were assessed seven months after impoundment. Water temperature, conductivity, pH, dissolved oxygen, transparency, nitrates, total nitrogen, orthophosphates, total phosphorus and metals (K, Na, Ca, Mg, Cu, Cd, Cr, Ni, Hg, Mn, Zn, Pb, Fe and As) were measured at five sites distributed across the Tugwi-Mukosi reservoir in July 2017. The reservoir was turbid after impoundment and had low water clarity. The trophic state of the reservoir ranged from eutrophic to marginally hypertrophic with high total phosphorus and total nitrogen concentrations. All measured physico-chemical water variables did not differ significantly between the lake sites with the exception of conductivity, ammonia and total phosphorus. Potassium, Na, Ca and Mg were high in the reservoir, whereas other heavy metals recorded low concentrations. Iron was relatively high with an average concentration of 0.24 mg l−1. The average Ca:K, Ca:Na and Ca:Mg ratios in the reservoir were 3.8, 1.1 and 3.2, respectively. The high Ca:Mg of 3.2 might favour the establishment of snails. Eutrophication of the Tugwi-Mukosi Reservoir should be abated through coordinated management of the reservoir and the terrestrial environment in the catchment to ensure that the water quality is able to support lake biodiversity and confer ecosystem services to human livelihoods around the reservoir. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]

In a study aimed to determine the histopathology, component parasite communities and level of selected heavy metals, African catfish Clarias gariepinus from three rivers in Zimbabwe (Gwebi, Manyame and Mukuvisi) were analysed for heavy metals (Cd, Cr, Cu, Fe, Ni, Pb, Zn) in the gills, liver, kidney and muscles. The histopathology of these tissues was assessed by microscopic examination of stained thin sections. Metazoan parasite diversity and species composition in fish along different sites of the rivers were determined and compared. Levels of Cd, Fe, Pb and Zn were lowest in the Gwebi, Cr and Cu in the Manyame, and Ni in the Mukuvisi River. There were significant differences (P < 0.5) in concentration of iron and nickel in the gill and liver tissues of fish among the three rivers while significant differences in concentration of iron and lead were observed in muscle tissue. Gill chronic inflammation and ossification were significantly different (P < 0.5) in fish from among the three rivers. Chronic inflammation, hemosiderin deposits and bile accumulation in the liver were also significantly different (P < 0.5) among the three rivers and so was the extent of chronic inflammation in the kidney tissue. Lamellar fusion was slightly more present in gills of catfish from the Mukuvisi than the Gwebi River. The parasite community of C. gariepinus comprised three monogenean, two cestode and three nematode species. The least polluted Gwebi River had the highest parasite community diversity while the most polluted Mukuvisi River had the lowest diversity. Fish parasite community structure is thus a potential indicator of river pollution, while heavy metal pollution is a potential threat to fish and human health in the system. [ABSTRACT FROM AUTHOR]

There is evidence that global warming is changing the thermal regimes of tropical lakes and this paper examines the impact of warming on the limnology of Lake Kariba. Between 1986 and 2011 the mean temperature of the lake rose by 0.7 °C, a rate equivalent to 0.03 °C y−1, but this increase was not uniform, being most pronounced in March and May (1.5 and 1.4 °C, respectively) and least in August and October (0.1 °C in both). These changes appear to have disrupted the thermal regime which now seems to be less predictable than before. Thermal gradients have weakened and, as a result, oxyclines are now less pronounced and persistent than in the past. Previous workers suggested that warming in Lake Kariba has strengthened stratification and has caused the thermocline to rise, reducing the volume of the epilimnion and thus reducing the productivity of the pelagic fishery. But this does not appear to be the case. Warming was not accompanied by more pronounced stratification or upward shift in the thermocline, but instead there was a downward transfer of heat that caused the thermocline to descend and weaken, thus reducing thermal stability. The dynamic nature of the thermocline highlights the need to exercise caution in making simple predictions and conclusions about biotic responses in a large complex ecosystem. [ABSTRACT FROM AUTHOR]

The invasion ofCherax quadricarinatus, the Australian redclaw crayfish, in the Sanyati Basin of Lake Kariba, Zimbabwe, is reported. A total of 79 crayfish were caught at 10 out of 12 sampling sites in the Sanyati Basin in November–December 2012. The average catch per unit effort (CPUE) varied from 1.1 to 4 crayfish per trap per night, carapace length ranged from 29 to 93.5 mm, and weight ranged from 4 to 196.2 g. Most crayfish were between 50 and 59.9 mm carapace length. Males (average 82.6 g) were significantly heavier than females (37.2 g) and males were larger in carapace length, carapace width, chela length and chela width. A feral population ofC. quadricarinatusis now established in the Sanyati Basin. Possible modes of dispersal within the basin are discussed. [ABSTRACT FROM AUTHOR]

Large branchiopods are considered threatened across much of their global range. However, because several regions, including Zimbabwe in general and its south-eastern lowveld in particular, remain largely unstudied, interpretations of species distribution patterns are often based on limited data. A detailed study of large branchiopods was carried out, with repeated sampling of 36 seasonal pans, in 2004-2008 in the Save Valley Conservancy, south-eastern lowveld. Sixteen large branchiopod species were collected, comprising eight Anostraca, one Notostraca, two Laevicaudata, four Spinicaudata and one cyclestherid species, representing 33% of all species known in southern Africa. Most species were new records for Zimbabwe. The enigmatic morphotype,Streptocephaluscf.bidentatus, was encountered for the first time in Zimbabwe, presenting an opportunity to resolve its taxonomic status.Streptocephalus wirminghausi, a species endemic to Zimbabwe, was also recorded. Large endorheic pans had higher species richness (an average of eight species) than small endorheic pans (average of six species), whilst floodplain pans housed fewest species (average of four species), probably due to predation by fish after floods. Since regional diversity and coexistence levels in the Save Conservancy were high, compared to other regions, this area should be considered a hotspot of large branchiopod diversity. [ABSTRACT FROM PUBLISHER]

Fish diversity in Malilangwe Reservoir in the south-eastern lowveld of Zimbabwe was investigated in 2011 to determine the community structure. The aim of this study was to determine the current status of an artificial fish community in a small reservoir that does not normally overflow and to assess how the fish have adapted to this environment. Eight species belonging to five families were collected from the reservoir. The cichlidsOreochromis mossambicus,O. macrochir,O. placidusandTilapia rendallimade up 46% by number of the sample, the cyprinidLabeo altivelismade up 40% of the sample, andT. rendalli, the least numerous species, made up 0.2% of the sample. The population ofT. rendalliseemed to be depleted, whereas largemouth bassMicropterus salmoides, which were formerly numerous, appeared to be absent.Oreochromis placidusbred throughout the study period, whereasClarias gariepinus,Hydrocynus vittatus,L. altivelis,O. macrochirandO. mossambicusshowed an apparent lack of recruitment between July and August 2011. The growth performances ofC. gariepinus,O. mossambicus,O. macrochirandO. placiduswere assessed by means of the growth performance index (φ′) with values ranging from 3.10 to 3.41. The rates of total mortality (Z) were estimated for four species; the highest rate was 5.64 forO. placidusand the lowest was 1.17 forC. gariepinus. [ABSTRACT FROM PUBLISHER]

The Lake Habitat Survey (LHS) method was developed to assess the ecological integrity of the physical habitat around lake and reservoir ecosystems, as well as to determine the magnitude of human pressure on lake systems. The LHS method has not previously been applied to tropical lakes but could potentially be a useful tool. The LHS approach was applied on a tropical African reservoir, Malilangwe reservoir, in 2011. The application of this methodology included the calculation of summary metrics Lake Habitat Metric Survey (LHMS) and Lake Habitat Quality Assessment (LHQA). Results show that although Malilangwe reservoir is experiencing increasing human pressure, it does not appear to suffer from a major invasion of alien plants. Its LHQA score, 76 out of 112, and LHMS score, 16 out of 42, are indicative of relatively few human pressures such as water pumping structures and residential areas. We conclude that the use of LHS can directly enhance the quality and reliability of hydromorphological assessments and can lead to better lake conservation and rehabilitation. It is clear that, for conservation management, a holistic assessment of naturalness, representativeness and species rarity needs to be made in conjunction with scoring systems. [ABSTRACT FROM AUTHOR]

Concentrations of zinc, cadmium, chromium, nickel, lead, copper and iron were measured in flowing water, riverbed sediments and tissues of sharptooth catfish Clarias gariepinus from three rivers in the upper Manyame catchment over seven months in 2008–2009. The Manyame and Mukuvisi rivers are severely polluted by industrial and domestic effluent, whilst the Gwebi River is not influenced by urban effluent. Key water quality parameters, including dissolved oxygen and conductivity, clearly showed a pollution gradient in the Mukuvisi and Manyame rivers, but water quality in the Gwebi River was good. Levels of zinc, iron, copper, nickel and lead in fish tissues from the three rivers sampled were unusually high, with zinc and iron concentrations being the highest in all the tissues. This was also positively correlated with the concentrations of these metals in water and sediments. Notable differences existed between the water (zinc and copper) and sediments (iron and zinc) of each river. The relatively high metal concentrations in the Gwebi River, as well as conductivity and dissolved ions, were explained by the geological influence of the Great Dyke in its subcatchment. Metals are bound in the sediment but these can be rapidly mobilised into water if environmental changes occur, therefore efforts to monitor and prevent further water quality deterioration are required. The results of this study may have significant negative implications for aquatic organisms and for human health through fish consumption and therefore risk assessment investigations are imperative. [ABSTRACT FROM PUBLISHER]

The article presents a study which examines changes in fish communities in association to flooding and drought in four floodplain pans in the Save Valley Conservancy in Zimbabwe. The study shows the possible occurrence of multiple pan connections which resulted to frequent fish migrations into and out of the pans. This indicates the adaptability of fishes to highly variable climatic regime. It suggests that natural conservation of the pans will help maintain their role in floodplain ecology.