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) Mon, 22 Nov 2021 16:18:32 +0000 OJS 60 A critical review of macroinvertebrate-based bioassessment approaches in Africa’s lotic systems: developments, challenges, and legal requirements <p>Worldwide, water resources have an impact on all forms of life as lotic systems are networks that interconnect water resources and land. They are important for navigation, water supplies, agriculture, recreation, and industrial development and help to regulate changes in climate and support social, spiritual, educational, and ecosystem health services. These ecosystems are, however, facing both natural and anthropogenic threats. Anthropogenic threats are driven by population increase, economic development, and catchment degradation. They are now the most threatened resources worldwide, and in Africa in particular. To design proper management strategies, the causes and impacts of the threats must be properly diagnosed. Monitoring and assessment approaches that show degradation and integrate it over time are essential to generate data and information required by water managers for decision making. Biomonitoring using macroinvertebrates is an effective tool in this regard, because it <br>integrates causes of degradation and aquatic biotic responses to the impacts thereof. This review summarises the needs, challenges, and legal implications of biomonitoring in Africa using lessons from countries with successful biomonitoring as benchmarks.</p> John Peter Obubu, Seyoum Mengistou, Tadesse Fetahi, Wolfram Graf, Robinson Odong Copyright (c) Mon, 22 Nov 2021 00:00:00 +0000 The impact of rubber effluent discharges on the water quality of a tropical rain forest river in Nigeria <p>The impact of a rubber effluent on the water quality of Oken River, Nigeria, was assessed. Surface water was analysed for water quality parameters at four sites; one upstream and three downstream. Significantly raised (p ≤ 0.05) levels of electrical conductivity, salinity, colour, turbidity, TSS, TDS, DO, COD, HCO<sub>3</sub>−, Ca, Cl, P, Mn, Cu, Pb and THC at the site immediately downstream of the pollution point source were recorded, with levels of colour, turbidity, Cd and Ni in all the stations higher than the WHO permissible limits. Principal component analysis (PCA) yielded 28 variables under six components that accounted for 92.33% of the total variance between sites. The PCA and water quality index (WQI) revealed significant influence by anthropogenic activities on the water quality of the river. Furthermore, the WQI output showed that the river water was not fit for human consumption. The cluster analysis revealed similarity in the physico-chemical conditions at Stations 1 and 4, whereas Stations 1 and 2 were the most dissimilar. This study advocates monitoring and protection of water bodies upstream and downstream of the influx of untreated effluents.</p> M.O. Omoigberale, I.M. Ezenwa, E. Biose, C. Okoye Copyright (c) Mon, 22 Nov 2021 00:00:00 +0000 Seasonal dynamics in water quality and phytoplankton of four tropical rivers in Ebonyi State, southeastern Nigeria <p>This study assessed the impacts of human activities and naturogenic processes on the water quality and phytoplankton of four rivers proximal to rice farms in Ebonyi State, south-eastern Nigeria. A range of water quality parameters were measured in conjunction with phytoplankton samples that were collected and identified in the laboratory using microscope and standard keys. The results showed that mean water temperature (30.32 ± 3.34 °C), conductivity (199.11 ± 118.70 μS cm<sup>−1</sup>) and total dissolved solids (102.60 ± 58.5 mg l<sup>−1</sup>) were highest in the dry season, while mean flow rate (0.7 ± 0.1 ms<sup>−1</sup>) and dissolved oxygen (6.15 ± 1.88 mg l<sup>−1</sup>) were highest in the wet season. Bacillariophyta had the highest mean abundance (6 611 ind. l<sup>−1</sup>) and biomass (5.52 μg l<sup>−1</sup>) in the dry season, whereas Chlorophyta had the highest mean diversity (Hʹ = 4.55) and species richness (MI = 1.1) in the wet season. Canonical correspondence analysis showed that hydrologic and climatic factors (temperature, water clarity and discharge) predominantly controlled phytoplankton community structure during the wet season while anthropogenic related factors (phosphate, nitrate and conductivity) regulated phytoplankton during the dry season. Consequently, sustainable management plans for these rivers must prioritise these factors in order to succeed.</p> G.N. Nwonumara, O.I. Okogwu Copyright (c) Mon, 22 Nov 2021 00:00:00 +0000 Seasonal variation in water quality, plankton diversity and microbial load of tropical freshwater lakes in Nigeri <p>Seasonal changes significantly affect tropical ecosystems; hence, verification of how these changes affect water quality is important for waterbodies that serve as water and food sources, particular as such changes are often associated with shifts in plankton diversity and microbial loads. This study assessed the seasonal changes in water quality, plankton diversity and microbial load in four lakes serving as sources of drinking water. Temperature, hardness and phosphate concentration were elevated in the dry season, and pH, biochemical oxygen demand, transparency, turbidity, total dissolved solids, conductivity, alkalinity and nitrate concentrations were elevated in the wet season. A phytoplankton analysis revealed that <em>Chlorophyta, Bacillariophyta, Cyanophyta and Dinophyta were most common, with the families Desmidiaceae, Microcystaceae and Euglenaceae (phylum Euglenophyta)</em> displaying dominance. For zooplankton, Rotifera was most common, with Branchionidae dominating the lakes in both seasons. In the wet season,<em> Chlorophyta, Cyanophyta, Bacillariophyta </em>and<em> Dinophyta</em> dominated, with <em>Aphanizomenonaceae </em>and<em> Microcystaceae</em> the most diverse families. Disease-causing pathogens, <em>Ascaridae, Trichuridae and Ancylostomatidae (phylum Nematoda)</em>, were detected during periods of high rainfall. The waters in the dry season had higher microbial loads than in the wet season, ranging from 1.50 to 233.50 CFU g<sup>−1</sup> (p &lt; 0.05). This demonstrates the seasonal variations in risk to users and underlies the importance of regular assessment of water quality particularly given the threat of seasonal changes elated to climate change.</p> Ihuoma N. Anyanwu, Confidence A. Ezema, Sowechi Ebi, Chinyere A. Nwajiuba, Okoro Nworie, Chioma O. Anorue Copyright (c) Mon, 22 Nov 2021 00:00:00 +0000 Phytoplankton community structure in relation to physico-chemical factors in a tropical soda lake, Lake Shala (Ethiopia) <p>Phytoplankton communities responses to physico-chemical factors were studied in Lake Shala from January to December 2018. Distinct spatial and seasonal variations were observed for all physico-chemical parameters, except DO (ANOVA: p &lt; 0.05). In total, 72 taxa, <em>Bacillariophyta</em> (55 taxa), <em>Chlorophyta</em> (seven taxa), <em>Cyanobacteria</em> (six taxa), <em>Euglenophyta</em> (two taxa), <em>Dinophyta</em> (one taxon) and <em>Charophyta</em> (one taxon) were identified. Phytoplankton abundance and biomass ranged from 5 789.3 cells ml<sup>–1</sup> to 1 516.2 cells ml<sup>–1</sup>, with a mean of 8 756.9 cells ml<sup>–1 </sup>and 9.8 μg l−1 to 25.8 μg l<sup>−1</sup>, with a mean of 17.1 μg l<sup>−1</sup>, respectively, and showed seasonal variations (p &lt; 0.05). Based on RDA analysis, most species were abundant in Shala Gike Shore station. Their distribution was negatively correlated with salinity and EC, whereas pH, alkalinity, NO<sub>3</sub>–N, SRP, TP, NH<sub>3</sub>–N and SiO<sub>2</sub> had a positive correlation. Previously Lake Shala was dominated by <em>Cryptophyta</em> but this has switched to a diatom-dominant community. Such changes in phytoplankton taxa may be suggestive of ecological change. This study provides baseline data on the phytoplankton community structure of Lake Shala associated with physico-chemical changes, against which future community structure can be evaluated.</p> Solomon Wagaw, Seyoum Mengistou, Abebe Getahun Copyright (c) Mon, 22 Nov 2021 00:00:00 +0000 Assessment of river health using benthic macroinvertebrates in the Dwars River, Olifants Water Management Area, Limpopo province, South Africa <p>The study assessed the impact of water and sediment quality on benthic macroinvertebrate assemblages in the Dwars River, a tributary of the Olifants River, Limpopo province, South Africa. Physico-chemical variables, heavy metals and macroinvertebrates were collected using standard methods. A multivariate analysis, Canonical Correspondence Analysis (CCA), was used to examine the macroinvertebrate community structure. Based on the selected physico-chemical variables and metal concentrations assessed, the water quality and sediment quality are deteriorating mainly in the downstream areas. The number of taxa and the Average Score per Taxon (ASPT) were significantly different between sites and seasons, with more taxa recorded in the upstream section of the river and in winter. A higher proportion of sensitive and high-scoring taxa (<em>Ephemeroptera, Plecoptera </em>and<em> Trichoptera</em>) were recorded in upstream and midstream sites and in winter. The CCA analysis showed an association of heavy metal concentration in the sediment with the distribution of macroinvertebrate taxa tolerant to poor water quality in the downstream section of the river. Because of the potential impacts of rapid economic development in the catchment, regular monitoring of the river is recommended, to detect potential river health problems early.</p> T.V. Mmako, A. Addo-Bediako, W.J. Luus-Powell, M. Kekana Copyright (c) Mon, 22 Nov 2021 00:00:00 +0000 Seasonal variation and drivers of zooplankton, macroinvertebrate and littoral fish communities from irrigation ponds in a semi-arid region in the Eastern Cape (South Africa) <p>Irrigation ponds are increasingly abundant globally, particularly in water-stressed countries with limited natural surface waters, yet knowledge of their ecology is limited. Here, we assessed zooplankton, macroinvertebrate, and littoral fish communities from irrigation ponds located in the Sundays River Valley in South Africa. This study assessed the seasonal community patterns in response to physico-chemical and biotic components. Water temperature, water depth, Secchi depth, and ammonium concentrations differed significantly across seasons. Similarly, Chlorophyll-a concentrations differed seasonally, with water transparency identified as the main driver. Zooplankton was dominated by <em>Rotifera, Copepoda</em> and <em>Cladocera</em>. Seasonal changes in temperature and subsequent fluctuations in water levels resulted in changes in zooplankton community. Macroinvertebrates were dominated by insects, notably the families <em>Corixidae </em>and<em> Naucoridae</em>. The littoral fish community comprised of <em>Glossogobius callidus, Oreochromis mossambicus </em>and<em> Gambusia affinis</em>. Zooplankton, macroinvertebrates and littoral fish abundances, species richness, diversity and assemblage composition differed significantly across seasons with temperature identified as the main driver of these differences. This study demonstrates that bottom-up processes are the dominant drivers of the irrigation pond communities in the Sundays River Valley and highlights the relevance of seasonal abiotic drivers in structuring these communities, particularly<em> G. callidus</em> and <em>G. affinis.</em></p> L. Mofu, T. Dalu, R.J. Wasserman, D.J. Woodford, D. Khosa, O.L.F. Weyl Copyright (c) Mon, 22 Nov 2021 00:00:00 +0000 Quality evaluation of Artemia cysts from three Algerian populations <p>The aim of this study was to determine the nutritional value of three populations of Artemia, one from the Bethioua Sebkha (Oran) and two new biotopes at El Melah (Bechar) and Timimoune (Adrar), by evaluating the cyst and nauplius biometry, hatching parameters and fatty acid profiles. This information is of relevance to aquaculture initiatives, and fills in knowledge gaps from previous research at Algerian sites. The size of nauplii varied from 453.26 ± 0.3 µm and 478.73 ± 0.2 µm. The chorion thickness was between 13.28 µm and 10.50 µm. The highest hatching percentage and hatching efficiency were obtained after decapsulation of Bethioua cysts. The shortest hatching synchrony time was also found for the Bethioua cysts. All cyst samples from the the Bethioua population analysed in this study showed a freshwater-type fatty acid profile, rich in linolenic acid (LNA, 18:3n.3), opposed to a marine-type fatty acid profile rich in presence of eicosapentaenoic acid (EPA, 20:5n<sup>-3</sup>). The Bethioua population exhibited the best hatching performance and are ideally suited for use in aquaculture.</p> C. Chabet Dis, W. Refes, I. Varó, F. Hontoria, F. Amat, J.C. Navarro Copyright (c) Mon, 22 Nov 2021 00:00:00 +0000 Rotifers in the Niger River, Niger: diversity and abundance in relation to environmental parameters <p>A first study of the rotifers of the Niger River in Niger is reported here. Two surveys took place under contrasting hydrological conditions: low-water level (16 April to 8 May 2018) and high-water level (1 to 15 February 2019). Zooplankton and physico-chemical parameters were sampled at eight stations spread over 520 km from Ayorou to Gaya. In total, 32 taxa were identified, including 26 at species level. During the low-water sampling, <em>Polyarthra sp. (31%), Brachionus caudatus (23%), Synchaeta longipes (11%), Keratella tropica (7%) and Filinia longiseta (5%) </em>were the most abundant, whereas <em>Brachionus quadridentatu s (26%), Lecane hastata (25%), Keratella cochlearis (9%), Keratella lunaris (5%), Hexarthra sp. (3%)</em> were dominant during the high-water sampling. The mean abundance of rotifers ranged between 14 × 10<sup>3</sup> ind. m<sup>−3</sup> during the high-water sampling and 244 × 10<sup>3</sup> ind. m<sup>−3</sup> during the low-water sampling. The highest diversity was observed in the three stations located upstream from the city of Niamey. The results reflect the difference in environmental parameters between the downstream and upstream Niamey stations. RDA analyses showed that the main environmental factors explaining the distribution of rotifers were dissolved oxygen, orthophosphate and nitrate concentrations.</p> H. Souley Adamou, B . Alhou, M. Tackx, F. Azémar Copyright (c) Mon, 22 Nov 2021 00:00:00 +0000 Bioaccumulation of trace metals in the ocypodid burrowing crab, <i> Paratylodiplax blephariskios</i>, in Richards Bay Harbour, South Africa <p>Bioaccumulation of metals in an endemic ocypodid burrowing mud crab, <em>Paratylodiplax blephariskios</em>, was investigated in contaminated mudflats of the subtropical Richards Bay Harbour (RBH), South Africa. Following sampling of water, sediment and mud crabs from three sites (Bhizolo, Mzingazi and Richards Bay Coal Terminal) in RBH during 2016/2017, tissue and sediment samples were oven dried for 48 hours, weighed and digested in an advanced microwave digester. Samples were then analyzed in triplicate for Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn using inductively coupled plasma optical emission spectrometry (ICP-OES). Highest tissue concentrations of Co, Cu, Mn, Ni, Pb and Zn were recorded at Bhizolo. High Biota Sediment Accumulation Factor (BSAF) values for Cd, Cu, Mn, Ni and Zn at all sites confirmed that crabs bioaccumulated these metals. The high Cr concentration in sediment (Bhizolo: 104 ± 18.2 µg g<sup>−1</sup>; Richards Bay Coal Terminal (RBCT): 104 ± 29.2 µg g<sup>−1</sup>; Mzingazi: 94.1 ± 38.7 µg g<sup>−1</sup>) was not reflected in the biota-sediment accumulation factor (BSAF) value, suggesting low bioavailability of Cr. High BSAF values for Cd, Cu, Mn, Ni and Zn suggest that the threshold of regulation in <em>P. blephariskios</em> was exceeded, resulting in net bioaccumulation.</p> J.I. Izegaegbe, L. Vivier, H.M.M. Mzimela Copyright (c) Mon, 22 Nov 2021 00:00:00 +0000 Comparative biotolerance of water spinach,<i> Ipomoea aquatica</i>, to heavy metal pollution in the Agodi Reservoir and the Ogunpa River, Oyo State, Nigeria <p>The biotolerance of water spinach (<em>Ipomoea aquatica</em>) to heavy metals was investigated in the Agodi Reservoir and its supplying source, the Ogunpa River, to examine the impact of aquatic pollution. <em>I. aquatica</em> was collected monthly from the Ogunpa River and the Agodi Reservoir. Atomic absorption spectrophotometry was used to analyse the concentration of heavy metals in the samples. A box plot was used to evaluate the tolerance of the plants to heavy metals and ecological risk quotients (ERQ) were calculated to indicate the threat to human health and environment. The concentrations of cobalt (Co), chromium (Cr), copper (Cu), nickel (Ni) and zinc (Zn) in the plants were below standard thresholds, but cadmium (Cd), iron (Fe), manganese (Mn) and lead (Pb) were present in higher than permissible levels. The ERQ of Cd in <em>I. aquatica</em> in the Ogunpa River was at an elevated ecological risk level in January (3.450), May (3.125), June (8.175), August (1.900) and September (2.025). The ERQ of Co, Cr, Cu and Ni inplants from both the reservoir and the river were less than one. The ERQ and biotolerance of heavy metals in this study indicated that <em>I. aquatica</em> is effective in binding heavy metals.</p> P.O. Ogungbile, P.O. Ayeku, O. Ajibare Copyright (c) Mon, 22 Nov 2021 00:00:00 +0000 Stock assessment of Nile tilapia <i>Oreochromis niloticus</i> (Linnaeus 1758) in Lake Tana, Ethiopia <p>Nile tilapia <em>Oreochromis niloticus</em> is a commercially important fish species in the Lake Tana fishery and contributes to 65% of the total annual catch. This study estimated the maximum sustainable yield (MSY) and effort at maximum sustainable yield (fMSY) for the <em>O. niloticus</em> fishery using the Thompson and Bell yield prediction model. Catch and effort data from four representative landing sites were collected daily from June 2016 to May 2017 and used to estimate the total mortality coefficient (Z) using catch curve analysis, natural mortality (M) using Pauly’s empirical formula, and fishing mortality (F) as F = Z − M. Population abundance was evaluated using the Jones length-based cohort analysis model. The estimated Z, M and F values were 1.1, 0.52, and 0.49 per year, respectively. In total, 5 077 tons of <em>O. niloticus</em> were produced, which exceeds the MSY of 4 904 tons per year that could be obtained from the fishery at an F0.1. Consequently, the recommendation is to reduce the fishing effort by 15%. Collection of catch-andeffort data from more landing sites, over an extended period, could improve the yield estimates and this should be considered in conjunction with a bioeconomic analysis in future.</p> A. Degsera, M. Minwyelet, T.G. Yosef Copyright (c) Mon, 22 Nov 2021 00:00:00 +0000