African Journal of Aquatic Science <p>The <em>African Journal of Aquatic Science</em> is an international journal devoted to the study of the aquatic sciences, covering all African waters. The Journal publishes peer-reviewed original scientific papers and short articles in all the aquatic science fields including limnology, hydrobiology, estuarine and coastal marine science. Amongst the topics covered in this Journal are ecology, conservation, bio-monitoring, management, water quality, ecotoxicology, biological interactions, physical properties and human impacts on aquatic systems. Supported by the Southern African Society of Aquatic Scientists, the <em>African Journal of Aquatic Science</em> serves as an indispensable reference source for those interested in understanding the dynamics affecting the valuable aquatic resources of Africa.</p><p class="MsoNormal">Subscriber access to this journal is available online <a href="" target="_blank">here</a></p> en-US Copyright for articles published in this journal is retained by the journal. (Publishing Manager) (Editorial Office) Wed, 28 Oct 2020 15:51:48 +0000 OJS 60 Letter: Statement from world aquatic scientific societies on the need to take urgent action against human-caused climate change, based on scientific evidence <p>No Abstract</p> Victor Wepener Copyright (c) Wed, 28 Oct 2020 00:00:00 +0000 Review Article: Trends in chemical pollution and ecological status of Lake Ziway, Ethiopia: a review focussing on nutrients, metals and pesticides <p>Aquatic ecosystems contribute to human well-being by delivering ecosystem services, but their protection has been given low priority in Africa. Lake Ziway in the Ethiopian Rift Valley basin provides services including irrigation, drinking water and fish food in the region. This paper reviews the biological resources and spatiotemporal variation of water quality of the lake focussing on nutrients, metals and pesticides. Lake Ziway is under increasing agricultural and urban pressure and is exhibiting deteriorating trends in several water quality and ecological parameters. Nutrients and trace metals, including PO<sub>4</sub><sup>3−</sup>, NO<sub>3</sub><sup>−</sup>, NH<sub>4</sub><sup>+</sup>, Ca<sup>2+</sup>, Cu and Ni of the lake have shown increasing temporal trends in concentration. Spatially, higher values of major parameters (e.g. NO<sub>3</sub><sup>−</sup>, NH<sub>4</sub><sup>+</sup>,K, Na and electrical conductivity) were observed at shoreline sites near floriculture farming. The water quality of the lake exceeded guideline values for drinking water (alkalinity and Fe) and for aquatic life (NH<sub>4</sub><sup>+</sup>, Fe, Cr, Cu and Se). The recently reported pesticides in the lake possibly cause ecological and human health effect. Accordingly, agriculture and urbanisation are affecting water quality of Lake Ziway, with likely negative effects on human health and the lake ecosystem function unless appropriate interventions are taken. Our results may be useful in assessing other African lakes subject to similar anthropogenic pressures in their catchments.</p> <p><strong>Keywords:</strong> African lakes, agriculture, ecological effect, ecosystem services, spatio-temporal variation, urbanisation, water quality</p> L.B. Merga, A.A. Mengistie, J.H. Faber, P.J. Van den Brink Copyright (c) Wed, 28 Oct 2020 00:00:00 +0000 Water quality of the volcanic crater lake, Lake Barombi Kotto, in Cameroon <p>Cameroon is endowed with many freshwater lakes and rivers but, because of increasing anthropogenic activities, most of these water bodies are gradually being degraded. Lake Barombi Kotto is one of the volcanic crater lakes in Cameroon that serves as a prime source of drinking water for the Barombi Kotto community. The overall objective of the study was to determine the water quality of Lake Barombi Kotto making use of some physico-chemical parameters, Carlson’s Trophic State Index (TSI), Heavy Metal Pollution index (HPI) and some bacteriological parameters. Water samples were collected over two seasons across a longitudinal transect at two depths and subjected to physico-chemical, bacteriological, nutrient, Chlorophyll a and phytoplankton analyses using standard methods. Descriptions, Analyses of Variance, ordinations and correlations were used to analyse resulting data at α = 0.05. Lake Barombi Kotto had a TSI of 93.67 and 87.92 in the dry and rainy season, respectively, indicating it is eutrophic. Of the six heavy metals studied, only the concentration of Fe was above the WHO (2008) drinking water quality limits. The HPI of the lake was 4.17 and 6.19 for the dry and rainy seasons, respectively, well below the critical index limit of 100. This lake is contaminated with faecal coliforms and pathogenic bacteria, such as <em>Salmonella</em>. This study has not only set baseline conditions for additional monitoring, but has exposed key dynamics and significant socio-economic and public health risks to humans.</p> <p><strong>Keywords:</strong> heavy metal pollution, Lake Barombi Kotto, microbiological contamination,<em> Microcystis</em> spp., pollution index, trophic state</p> M.E. Awo, B.A. Fonge, P.T. Tabot, J.T.K. Akoachere Copyright (c) Wed, 28 Oct 2020 00:00:00 +0000 Physico-chemical limnology during the filling phase of Tugwi-Mukosi, a tropical reservoir in Zimbabwe <p>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<sup>−1</sup>. 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.</p> <p><strong>Keywords:</strong> aging, artificial reservoir, eutrophic, limnological, marginally hypertrophic, physico-chemical</p> L Mhlanga, T.C. Madzivanzira, T Nhiwatiwa, P Tendaupenyu, M Barson, L Marufu, N Songore Copyright (c) Wed, 28 Oct 2020 00:00:00 +0000 Spatio-temporal distribution of organochlorine pesticide residues in water and sediments of tropical reservoirs: a case study of Bui Reservoir, Ghana <p>This study investigated the spatio-temporal distribution of organochlorine pesticides (OCPs) in water and sediments of the Bui Reservoir from June 2017 to May 2018, to provide baseline data for monitoring contamination in the Reservoir. Samples were collected during four seasons reflecting levels of rainfall and from five sites around the Reservoir. Water and sediment samples were subjected to liquid-liquid separation and ultrasonic extraction, respectively. GC-ECD was used to identify and quantify the pesticide residues. Eight OCPs each for water and sediment were detected and their concentrations in water and sediment range from 0.1–4.6 µg l<sup>−1</sup> and 1.38–104.86 ng g<sup>−1</sup> dry weight, respectively. α-Hexachlorocyclohexane and trans-chlordane dominated with mean concentrations of 3.2 ± 0.08 µg l<em>−1</em> and 70.91 ± 3.47 ng g<sup>−1 </sup>dry weight in water and sediment, respectively. There were non-significant differences (<em>p</em> &gt; 0.05) in the spatial distribution of OCPs in water and sediments, but significant differences (<em>p</em> &lt; 0.001) in the temporal distribution of the contaminants in water and sediments, with the wet season samples accounting for the highest concentrations. This indicated that the distribution, behaviour and fate of OCPs the the reservoir have close links with meteorological properties beyond their chemical composition.</p> <p><strong>Keywords:</strong> aquatic system, desorption, environment, hydrophobic, influx, metabolite, temperature, volatilisation</p> S.B. Jidauna, R Edziyie , B.B. Campion Copyright (c) Wed, 28 Oct 2020 00:00:00 +0000 Spatio-temporal typology of the physico-chemical parameters of a large North African river: the Moulouya and its main tributaries (Morocco) <p>The physico-chemical parameters of surface water from the largest Maghrebian river flowing into the Mediterranean Sea, the Moulouya River, show a large variability in space and time, under the influence of natural and anthropogenic phenomena. This study was conducted between March and August 2014, and involved regular bimonthly monitoring of nine abiotic parameters in each of the 45 selected stations along the Moulouya River and its main tributaries: the Anzegmur, Melloulou and Za rivers. The use of inter- and intraclass analyses facilitates the interpretation and understanding of the spatio-temporal variability of these physico-chemical descriptors and highlights the evolution of their spatial structure, and supported by the statistical analyses. In this study, a dominant spatial typology marked by a reduced temporal influence is highlighted. In terms of comparisons between the four rivers studied, the results show that the water quality in the Anzegmur and Melloulou Rivers is good with little or no pollution if judged by the Moroccan standards of the quality of the surface waters. In contrast, the water quality in the Za River and the main Moulouya River is degraded. High concentrations of organics were recorded at the M6, M8, M12 and Z11 stations, which receive untreated wastewater from the rural communes of Zaïda and Missour and the urban communes of Guercif and Taourirt, respectively. Improvement of water management in North African catchments is therefore recommended and suggestions are given herein.</p> <p><strong>Keywords:</strong> Anzegmur River, inter- and intraclass analyses, Melloulou River, organic discharges, spatial typology, Za River</p> Taybi Abdelkhaleq Fouzi, Mabrouki Youness, Legssyer Bouchra, Berrahou Ali Copyright (c) Wed, 28 Oct 2020 00:00:00 +0000 Assessment of the ecological status of the Kinyankonge River (Burundi), using a Biotic Integrity Index of zooplankton (BII-zooplankton) <p>This study aimed at assessing the ecological status of the Kinyankonge River using a zooplankton-based Biotic Integrity Index (BII-zooplankton). This was achieved through monthly collections of zooplankton from four stations along the river over 18 months (from July 2015 to June 2016, then from January 2017 to June 2017). Chemical parameters of the water were also measured using the AFNOR and APHA methods. Organic loads of water samples were assessed using Leclercq’s Organic Pollution Index. Zooplankton levels of disturbance were evaluated by Karr’s Biological Integrity Index. From this study, it was calculated that the Organic Pollution Index had two levels of pollution: strong organic pollution and very high organic pollution for upstream and downstream stations, respectively. Zooplankton populations were more disturbed during dry season than rainy season. The calculated Biotic Integrity Index highlighted a degradation of the ecological quality, especially in the upstream stations along the Kinyankonge River. Based on the zooplankton species diversity as an indicator of the ecological status of the river, the Biotic Integrity Index revealed a spatio-temporal variation highlighting four states of ecological quality of the Kinyankonge River: bad, moderate, good and very good, where <em>Microcyclops</em> sp. indicates bad ecological status,<em> Brachionus angularis</em> and <em>Tropocyclop</em>s sp. indicate moderate ecological status, whereas <em>Rotaria</em> sp. indicates very good ecological status. No species was identified as indicator of good ecological status. Therefore, the BII-zooplankton can be used as an indicator of the ecological health of the Kinyankonge River, and extended to other aquatic ecosystems in Burundi.</p> <p><strong>Keywords:</strong> bioindicators, pollution, rotifers, seasons</p> S Buhungu, C Sibomana, D.C. Adjahouinou, G Ntakimazi, C.A. Bonou, E Montchowui Copyright (c) Wed, 28 Oct 2020 00:00:00 +0000 Plankton Index of Biotic Integrity (P-IBI) for assessing ecosystem health within the Ouémé River basin, Republic of Benin <p>This study aims at assessing the impact of organic pollution on plankton communities of the Ouémé River using a Plankton Index of Biotic Integrity (P-IBI) as a tool for ecological heath assessment. Plankton and other environmental data were collected monthly from October 2014 to September 2015. An Organic Pollution Index (OPI) was calculated to classify the sampling sites, and 18 plankton candidate metrics were used to discriminate among the observed organic pollution levels. From this analysis, seven significant metrics were selected for setting up biotic integrity indices. An indicative value (IndVal) was calculated for each plankton species to identify indicator species characteristic of observed ecological statuses. The OPI shows significant organic pollution at sites, such as Kaboua, Vossa and Atchakpa-rejet, and less organic pollution at Kpassa. The plankton Index of Biotic Integrity (P-IBI) value shows significant correlation (<em>r</em> &gt; 0.75) with organic pollution. Three ecological states were identified: Kaboua and Vossa were in fair condition; Kpassa, Toué, Atchérigbé and Affon in very good condition; and all other sites in good condition. Three phytoplankton and four zooplankton species were significantly associated with good conditions, whereas 108 phytoplankton species and 40 zooplankton species were significantly associated with fair conditions within the River basin.</p> <p><strong>Keywords:</strong> anthropogenic impact, bioindicator, phytoplankton, water pollution, zooplankton</p> A.M. Houssou, D.C. Adjahouinou, C.A. Bonou, E Montchowui Copyright (c) Wed, 28 Oct 2020 00:00:00 +0000 A survey of phytoplankton and zooplankton communities in the newly created Tugwi-Mukosi reservoir, Zimbabwe, during the filling phase <p>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 <em>Microcystis aeruginosa</em> and <em>Aulacoseira granulata</em>, whose abundances ranged from 3 200−28 800 ind. l<sup>−1</sup> and 1 640−3 146 ind. l<sup>−1</sup>, 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 &lt;1 ind. l<sup>−1</sup> 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 <em>Diaphanosoma excisum</em> and <em>Ceriodaphnia cornuta</em>, were the most abundant followed by copepods, mainly <em>Thermoclops</em> sp. and <em>Eodiaptomus japonicas</em>. The dominance of <em>Microcystis aeruginosa</em> 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.</p> <p><strong>Keywords:</strong> aging, artificial reservoir, eutrophic, <em>Microcystis aeruginosa</em></p> L Mhlanga, T.C. Madzivanzira, T Nhiwatiwa, P Tendaupenyu, M Barson, L Marufu, N Songore Copyright (c) Wed, 28 Oct 2020 00:00:00 +0000 Cyanobacterial abundance and microcystins in water, seston and fish tissues in Lake Hora-Arsedi (Ethiopia) <p>The phytoplanktonic composition with a focus on cyanobacteria, intra- and extracellular microcystins (MCs) concentrations and MCs concentrations in fish tissues were investigated in Lake Hora-Arsedi (Ethiopia). The phytoplankton community comprised of 40 species in the first phase of the study and was dominated by cyanobacteria and dinoflagellates. Considerable concentrations of both intra- and extracellular MCs were detected. Total extracellular MCs concentrations in water of up to 2.99 µg l<sup>−1</sup> were detected, with the highest level almost three times the WHO tolerable daily intake (TDI) limit for MC-LR in drinking water. The MCs concentration in algal seston measured in April 2015, 1.138 µg g<sup>−1</sup> dry weight (DW), was higher than that recorded in March 2015 (0.825 µg g<sup>−1</sup> DW). Among the three MCs congeners for which we had standards, MC-LR and MC-YR accounted for 71.5 and 28.5%, respectively, of the total MCs measured in the water samples, whereas MC-RR was below the detection limit of the method of analysis used. The total MC concentration in the liver of <em>Oreochromis niloticus</em> was 14.42 µg g<sup>−1</sup> DW in March although the MC concentration in April was not measurable in the liver sample of the same species, <em>O. niloticus</em>. Conversely, the total MC concentrations in the liver samples of <em>Tilapia zillii</em> collected in March and April were 15.21 and 17.8 µg g<sup>−1</sup> DW, respectively. The results suggest that there is considerable potential for knock-on effects of toxic algae blooms on humans through consuming water and fish from Lake Hora-Arsedi.</p> <p><strong>Keywords:</strong> algae, composition, Oreochromis niloticus, physico-chemical properties, phytoplankton, water quality</p> T.W. Zewde, D Kifle, J.A. Johansen, T.B. Demissie, J.H. Hansen, Z Tadesse Copyright (c) Wed, 28 Oct 2020 00:00:00 +0000 Water hyacinth (<i>Eichhornia crassipes</i>) affects the composition and abundance of zooplankton in the littoral region of Koka Reservoir, Ethiopia <p>Water hyacinth, <em>Eichhornia crassipes</em> (Martius) Solms 1883, is a rampant invasive aquatic plant that is recognised as one of the ten worst weeds in the world. Its appearance in Koka Reservoir was reported in 1965 and since then it has become a major threat to the aquatic ecosystem. Despite numerous limnological studies on Koka Reservoir, the effects of water hyacinth on zooplankton has not been addressed previously. To assess this, samples were collected from three weed-infested and three non-infested sites from March to July 2018. The zooplankton community living, which was constituted of 38 species, was dominated by Rotifers, followed by copepods and cladocerans at both sites. The variations in the abundance of zooplankton and species richness (<em>d</em>) between the two sites were significant with higher mean values in the non-infested sites (<em>p</em> &lt; 0.05). The existing infestation level of water hyacinth poses a significant effect on the composition and abundance of zooplankton. Therefore, continuous follow-up, such as physical removal of the weed and constructing buffer zone and designing sustainable management strategies, have to be addressed.</p> <p><strong>Keywords:</strong> biomass, community structure, ecosystem, foodweb</p> H Getnet, D Kifle, T Fetahi Copyright (c) Wed, 28 Oct 2020 00:00:00 +0000 Changing patterns of <i>Schistosoma</i> host snail population densities in Maun, Botswana <p>Changes in the inflow of water into the Thamalakane River had been predicted to alter snail population dynamics and influence the risk of schistosomiasis transmission in Maun. We determined the abundance of schistosome intermediate host snails along the Thamalakane River and evaluated the risk of schistosomiasis infection within Maun. A retrospective study utilised snail survey data previously collected from the Thamalakane River in Maun between June 2009 and July 2012. A total of 3 563 freshwater snails were collected from 10 sentinel sites along Thamalakane River. The snails collected were <em>Bulinus globosus</em>, <em>Biomphalaria pfeifferi</em>, <em>Lymnaea natalensis</em>, <em>Bellamya capillata</em>, <em>Pila occidentalis</em> and <em>Lanistes ovum</em>. <em>Bulinus globosus</em> snails were more abundant than <em>B. pfeifferi</em>. None of the intermediate host snails (IHS) collected shed cercariae. The absence of infected IHS suggests that there was no active transmission of schistosomiasis during the study period. Furthermore, the presence of <em>B. globosus</em> in the Thamalakane River suggests the potential risks of <em>Schistosoma haematobium</em> infection when transmission conditions become conducive.</p> <p><strong>Keywords:</strong> abundance, <em>Biomphalaria pfeifferi</em>, <em>Bulinus globosus</em>, schistosomiasis</p> M.J. Chimbari, C Kalinda, N Siziba Copyright (c) Wed, 28 Oct 2020 00:00:00 +0000 Host selection and notes on the distribution of <i>Chonopeltis australis</i> Boxshall, 1976 in southern Africa <p>The parasite <em>Chonopeltis australis</em> Boxshall, 1976 has been recorded from tributaries of the Orange-Vaal River System. It is host-specific, preferring the cyprinids <em>Labeo capensis</em> (Smith, 1841) and<em> Labeo umbratus</em> (Smith, 1841). Sampling was conducted between spring 2016 and autumn 2019 at various sites on the main stream of the Vaal River. The current study considers current ecological data and compares these to historic data. The species produces a single cohort, with overwintering eggs and adults. The infection of<em> L. capensis</em> peaks in autumn. Parasites aggregate on larger hosts that occur in riverine habitats, but can succeed in shallow impoundments with suitable hard surfaces for egg deposition. This parasite exploits changes in ecological conditions and host biology in order to survive, but will only choose between these two host species where they aggregate on larger hosts. The increased pollution in the Vaal River Barrage and downstream has had an impact on the occurrence of <em>C. australis</em> and it is possibly extirpated in polluted parts of the river.</p> <p><strong>Keywords:</strong> distribution, extirpation, host specificity, riverine, seasonality, Vaal River fish parasite, water quality</p> L.A.M. Neethling, A Avenant-Oldewage Copyright (c) Wed, 28 Oct 2020 00:00:00 +0000 Age and growth of Nile tilapia <i>Oreochromis niloticus</i> (Linnaeus, 1758) from Lake Tana, Ethiopia <p>Age and growth of Nile tilapia, <em>Oreochromis niloticus</em>, from Lake Tana were studied from June 2016 to May 2017. In total, 1 597 otoliths were collected from three representative sampling sites for macrozone analysis. Otoliths were ground and examined under a dissecting microscope at 7–40× for the presence of translucent and opaque macrozones using a reflected light source. The age of the fish was determined from the total number of translucent macrozones counted in the otoliths considering the time of translucent zone formation and median hatch date. Two peaks of translucent macrozones were observed in January and February and in June and July. The mean marginal increment was found to be highest (73–85%) in November, December and May, and lowest (0–9.3%) in January, February, June and July. The von Bertalanffy Growth Function was fitted to observed length and age, with L<sub>∞</sub> = 45.1 cm, K = 0.21 y<sup>−1</sup> and t<sub>0</sub> = −0.514 years. The growth rate for <em>O. niloticus</em> from Lake Tana was lower than that previously reported for Ethiopia, warranting additional studies to determine causative factors that would explain the differences.</p> <p><strong>Keywords:</strong> biannuli, growth rate, Lake Tana fishery, macrozone, otolith</p> A Degsera, M Minwyelet, T Yosef Copyright (c) Wed, 28 Oct 2020 00:00:00 +0000 Cadmium and lead levels in three freshwater fish species from the Zambezi region, Namibia <p>Muscle tissue from three-spotted tilapia (<em>Oreochromis andersonii</em>) (<em>n</em> = 11), sharp tooth catfish (<em>Clarias gariepinus</em>) (<em>n</em> = 14) and tigerfish (<em>Hydrocynus vittatus</em>) (<em>n</em> = 12) were sampled from a market in the Zambezi region, Namibia in June 2018 and analysed for cadmium and lead. Cadmium was not detected in the three fish species. Mean lead levels in all three fish species (0.09–0.19 mg kg<sup>−1</sup>) were below the recommended safe level of 0.3 mg kg<sup>−1</sup>. Catfish had the highest mean lead concentrations, followed by tigerfish and tilapia in descending order. However, the differences in mean lead concentrations between the three fish species were not statistically significant (ANOVA,<em> p</em> = 0.18). These results show that the fish tested were safe for human consumption with respect to the metals tested. It is recommended that more metals and other contaminants, such as pesticides, be monitored robustly in water, sediment and fish, using the recommended protocols, in order to generate data that can be reliably used for human health risk assessments in the future.</p> <p><strong>Keywords:</strong> edible, fish muscle, river, sharp tooth catfish, three-spotted tilapia, trace metals, tigerfish</p> O Madzingira, L.Z. Lifumbela, E Kandiwa, L Kandjengo, B Mushonga Copyright (c) Wed, 28 Oct 2020 00:00:00 +0000