African Journal of Aquatic Science https://www.ajol.info/index.php/ajas <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="http://www.nisc.co.za/products/2/journals/african-journal-of-aquatic-science" target="_blank">here</a></p> en-US Copyright for articles published in this journal is retained by the journal. publishing@nisc.co.za (Publishing Manager) ajas.editor@nisc.co.za (Editorial Office) Sat, 14 May 2022 09:04:07 +0000 OJS 3.1.2.4 http://blogs.law.harvard.edu/tech/rss 60 Development of a multimetric index for assessing the ecological integrity of some selected rivers and streams in the north-eastern part of Lake Tana sub-basin, Ethiopia https://www.ajol.info/index.php/ajas/article/view/225192 <p>A multimetric index was developed using benthic macroinvertebrates to assess the ecological health of selected rivers and streams in the north-eastern part of Lake Tana subbasin, Ethiopia. One-time extensive sampling was carried out during the post-rainy season (November–December) of 2016. Macroinvertebrates were collected using a Surber sampler and a D-frame net at twenty sites. Based on the measured physico-chemical variables, sampling sites were clustered into references (<em>n</em> = 8) and test sites (<em>n</em> = 4). Approximately thirty potential candidate metrics were tested, and five metrics were selected as core metrics: number of Ephemeroptera Plecoptera Trichoptera taxa, percentage of Ephemeroptera individuals, percentage of EPT individuals, percentage that were shredders, and the percentage that were filter-feeders. These metrics were scored on a continuous scale from 0 to 10. To develop Lake Tana subbasin multimetric index (LTSBMI), scores were added and scaled to produce a score from 0 to 100. The final index was divided into five water quality classes: 'very good', 'good', 'fair', 'poor' and 'very poor'. The LTSBMI was effective in discriminating sites with different levels of impacts, but should be checked to other localities. The current LTSBMI could be used for ecosystem health assessment and monitoring in different Aftropical river systems with similar agroecology.</p> Amelework Zewudu, Getachew Beneberu, Minwyelet Minigst, Amare Mezgebu Copyright (c) https://www.ajol.info/index.php/ajas/article/view/225192 Sat, 14 May 2022 00:00:00 +0000 Use of biological and water quality indices to evaluate conditions of the Upper uMngeni Catchment, KwaZulu-Natal, South Africa https://www.ajol.info/index.php/ajas/article/view/225193 <p>Urban and agricultural land uses have the potential to severely compromise the quality of impoundments, if ineffectively managed and operated. A case in point is the upper uMngeni Catchment, including Midmar Dam, which is integral to the freshwater supply infrastructure in KwaZulu-Natal, South Africa. Monitoring sites were established in varying land use types in three subcatchments of the upper uMngeni Catchment to assess water quality and ecosystem health impacts of current land uses. Conclusions about water quality were drawn using pairing of SASS5 and spot water quality data. Water quality and ecological condition were highest in commercial plantations and upstream of a high-density settlement where natural land cover and sparse settlement occurred. Although marked declines in water quality and ecological condition were observed under commercial agriculture. The most notable declines in water quality and ecological condition were observed downstream of the settlement with elevated nutrient loads. Shifts in aquatic biota were highly correlated with seasonal shifts in water quality, influenced markedly by land use. The cumulative effects of current land use activities, urban development and agriculture on Midmar Dam’s water quality should be viewed with concern. Additional development in the form of additional social housing projects may exacerbate impacts.&nbsp;</p> R van Deventer, CD Morris, TR Hill, NA Rivers-Moore Copyright (c) https://www.ajol.info/index.php/ajas/article/view/225193 Sat, 14 May 2022 00:00:00 +0000 Macroinvertebrate community structure and diversity in relation to environmental factors in wetlands of the lower Gilgel Abay River catchment, Ethiopia https://www.ajol.info/index.php/ajas/article/view/225194 <p>The influence of environmental factors on the diversity of macroinvertebrates was studied in the wetlands of the Gilgel Abay River (GAR) catchment in Ethiopia. The study was done between September 2017 and March 2018, encompassing both wet and dry seasons. Six study wetlands from the GAR catchment were selected in a targeted manner based on the surrounding land use, exposure to anthropogenic disturbances and accessibility to conduct a quantitative study. The relationships between biological and environmental variables were evaluated by using multivariate analyses. Altogether, 36 families of macroinvertebrates were identified. Macroinvertebrate diversity indices were significantly higher at less impaired sites, compared with more impaired sites. Several families of Ephemeroptera, Odonata and Trichoptera taxa, including Corduliidae, Calopterygidae, Baetidae, Aeshnidae, Polymitarcyidae, Hydropsychidae, Heptageniidae, Polycentrapodidae, Hydroptilidae and Philopotamidae were negatively correlated with organic and inorganic pollutants and human disturbances and might be considered as potential indicators of less impaired sites. Conversely, the families Chironomidae, Hirudinidae and Libellulidae were positively correlated with biological oxygen demand, ammonium and human disturbance score and negatively correlated with dissolved oxygen. Generally, results of acroinvertebrate diversity and composition in this study indicate poor ecological condition of the wetlands, particularly those adjacent to agricultural and urban areas.</p> Habtamu Getnet, Seyoum Mengistou, Bikila Warkineh Copyright (c) https://www.ajol.info/index.php/ajas/article/view/225194 Sat, 14 May 2022 00:00:00 +0000 Macrophyte species diversity and distribution in relation to water quality of the Cheleleka Wetland in Ethiopia https://www.ajol.info/index.php/ajas/article/view/225195 <p>The Cheleleka Wetland is located in the Ethiopian Rift Valley on the upper shore of Lake Hawassa, after which the regional capital is named. This study investigated the relationship between water quality and the occurrence and diversity of macrophyte species of the wetland. Spatio-temporal variability in terms of water quality and macrophytes were studied in the wet and dry seasons at purposely-selected sites selected based on human disturbance levels. Six sites were selected, two from each of ‘severely’, ‘moderately’ and ‘least disturbed’, and data collected on water quality parameters, macrophytes richness and abundance. The results showed 25 macrophyte species dominated by Cyperaceae (24%), Poaceae (20%) and Nymphaeaceae (12%). Species diversity and abundance were significantly different between seasons and among the sampling sites (<em>p</em> &lt; 0.05), with the richest taxa recorded at the least disturbed sites. A redundancy analysis of the species–environment relationships identified nutrient loads as significant drivers of macrophyte diversity and abundance in the wetland. Generally, the results showed the spatial and temporal variation of macrophyte diversity and abundance are affected by water quality, and poor water quality has resulted in poor ecological conditions of the Cheleleka Wetland.</p> Haymanot Tesfaye, Bikila Warkineh Copyright (c) https://www.ajol.info/index.php/ajas/article/view/225195 Sat, 14 May 2022 00:00:00 +0000 Assessing fish community response to water quality and habitat stressors in KwaZulu-Natal, South Africa https://www.ajol.info/index.php/ajas/article/view/225196 <p>The degradation of freshwater ecosystems can be attributed to stressors associated with the increased demand for water and other aquatic resources. Freshwater ecosystems face such challenges in supporting agriculture, industry, and high-density urban areas in KwaZulu-Natal (KZN) province, South Africa. In this study, the presence of fish species and their abundance was quantified at 40 sites in KZN on 16 major rivers systems. Surveys were done during a drought period between February 2015 and April 2016, as part of the River Health Programme, a national river monitoring assessment. The Fish Response Assessment Index (FRAI) was used to evaluate the condition of the sites, and redundancy analysis was used to evaluate the habitat, water quality and fish community relationships. The FRAI scores showed four sites to be in a ‘Seriously Modified’ condition. These areas were associated with intensive agricultural activities and urban environments. The presence of invasive fish species, abstraction and industrial use all had negative impacts on the ecological state of the rivers. When compounded by excessive water use, the drought resulted in poor fish community integrity, highlighting the vulnerability of fish communities in this region. The absence or low abundances of some indigenous fish alongside the high presence of invasive fish requires additional investigation. Results highlight the importance of mitigation measures against anthropogenic impacts should be enforced to ensure sustainable use of KZN water resources.&nbsp;</p> Wesley Evans, Colleen T Downs, Matthew J Burnett, Gordon C O’Brien Copyright (c) https://www.ajol.info/index.php/ajas/article/view/225196 Sat, 14 May 2022 00:00:00 +0000 Estimation of pesticide mixture interaction in Nile tilapia (<i>Oreochromis niloticus</i>) using survival analysis https://www.ajol.info/index.php/ajas/article/view/225197 <p>The acute toxicity of the pesticides atrazine, mancozeb, chlorpyrifos and lambda-cyhalothrin, acting singly and jointly, was assessed on Nile tilapia (<em>Oreochromis niloticus</em>) fingerlings. Median lethal concentration (LC<sub>50</sub>), median lethal time (LT<sub>50</sub>), and mixture interaction were estimated, whereas survival analysis was used to model time-todeath. The most toxic single and joint mixture was lambda-cyhalothrin and chlorpyrifos-lambda cyhalothrin, respectively. The risk of death (RoD) of fingerlings exposed to 9.22 mg l<sup>−1</sup> atrazine-mancozeb mixture was 1.76 times higher than fingerlings exposed to 9.0 mg l<sup>−1</sup> atrazine (<em>p</em> &gt; 0.05). However, RoD of fingerlings exposed to 9.95 mg l<sup>−1</sup> atrazine-chlorpyrifos was 5.59 times higher than fingerlings exposed to 9.0 mg l<sup>−1</sup> atrazine (<em>p</em> &lt; 0.01). The risk of death of fingerlings exposed to 20.8 mg l<sup>−1</sup> atrazine-lambda cyhalothrin was 2.81 times higher than 21.0 mg l<sup>−1</sup> atrazine. The toxicity of 2.3 mg l<sup>−1</sup> mancozeb-chlorpyrifos was 254.25 higher than 2.2 mg l<sup>−1</sup> mancozeb (<em>p</em> &lt; 0.01). Fingerlings exposed to 4.33 mg l<sup>−1</sup> mancozeb-lambda cyhalothrin and 0.177 mg l<sup>−1</sup> chlorpyrifos-lambda cyhalothrin mixture were 0.02 and 0.14 times less likely to die than those exposed to 4.8 mg l<sup>−1</sup> mancozeb and 0.17 mg l<sup>−1</sup> chlorpyrifos, respectively (p &lt; 0.01). Atrazine-mancozeb, atrazine-chlorpyrifos, atrazine-lambda cyhalothrin, and mancozeb-chlorpyrifos interaction were synergistic, and their relative risk was &gt;1. Both mancozeb-lambda cyhalothrin and lambda-cyhalothrin-chlorpyrifos mixtures were antagonistic, and their relative risk was less than 1. Survival analysis can show interaction in complex pesticide mixtures.</p> KC Kanu, NH Amaeze, AA Otitoloju Copyright (c) https://www.ajol.info/index.php/ajas/article/view/225197 Sat, 14 May 2022 00:00:00 +0000 The effect of rainbow trout (<i>Oncorhynchus mykiss</i>) invasions on native fish communities in the subtropical Blyde River, Mpumalanga province, South Africa https://www.ajol.info/index.php/ajas/article/view/225198 <p>This study investigated the effects of rainbow trout (<em>Oncorhynchus mykiss</em>) invasion on native fish communities in the upper Blyde River catchment. A fish survey was undertaken between September 2017 and October 2018 from 11 sites in the Blyde and Treur Rivers using electrofishing and fyke nets. Differences in species composition, relative abundance, and community structure among sites were tested using multivariate analysis. A total of ten fish species were captured. There were significant differences in composition and abundance between fish communities that could be attributed to <em>O. mykiss</em> invasion and variation in habitats. Populations of native species that historically occurred throughout the upper catchment, such as Enteromius treurensis, were greatly reduced and fragmented in the presence of <em>O. mykiss</em>. However, instream migration barriers such as waterfalls have prevented upstream migration of <em>O. mykiss</em>, and these invasion-free areas have remnant populations of native fishes that appear to be largely intact. This finding is consistent with other studies that have shown that introduced alien predatory fish can have a significant effect on fish communities and highlighted the need to prevent human-facilitated introductions in biodiversity sensitive areas, such as mountain headwater streams, that are inhabited by endemic and range-restricted minnows.</p> Lerato T Maimela, Christian T Chimimba, Tsungai A Zengeya Copyright (c) https://www.ajol.info/index.php/ajas/article/view/225198 Sat, 14 May 2022 00:00:00 +0000 Tidal influence on fish faunal occurrence and distribution in an estuarine mangrove system in Ghana https://www.ajol.info/index.php/ajas/article/view/225199 <p>This study assessed the effects of tidal stages and habitat conditions on nekton assemblage and distribution in the Kakum River estuarine mangrove system in the Central Region of Ghana. Teleosts and crustaceans were sampled using pole seine and cast net from a tidal mangrove pond and a channel, and characterised using morphometry and ecological guilds concept. In total, 1 146 specimens were collected, with 35 species from 19 families represented. The most abundant species encountered were <em>Liza</em> spp. (Mugilidae; 36%), <em>Sarotherodon melanotheron</em> (Cichlidae; 16%), <em>Elops lacerta</em> (Elopidae; 6%) and <em>Sardinella aurita</em> (Clupeidae; 5%), which exhibited pronounced spatial distribution. <em>Sarotherodon melanotheron</em> showed preference for ponds with minimal water flow and depth, <em>Sardinella aurita</em> occurred only in deeper sections of the mangrove channel with significant flow velocity, and <em>Elops lacerta</em> in the pond and all channel stations. Mugilids were found exclusively in the channel, whereas Palaemonidae (<em>Macrobrachium macrobrachion</em> and <em>M. vollenhoveni</em>) occurred in specific locations in the channel, with speciesspecific preferences for tidal stages. Most species encountered were identified to be predominantly marine migrants with bentophagous feeding habit. Site selection and tidal stages were found to affect the occurrence and distribution of fishes over a tidal cycle and interactively influence species diversity.</p> NK Asare, JL Javier Copyright (c) https://www.ajol.info/index.php/ajas/article/view/225199 Sat, 14 May 2022 00:00:00 +0000 Structural assemblages of plant species in the Owabi Ramsar Wetland in the Ashanti Region of Ghana https://www.ajol.info/index.php/ajas/article/view/225200 <p>Anthropogenic activities as predictors of species assemblages in the Owabi Ramsar Wetland were investigated between May and September 2019. Data were collected in 154 plots at five different sites. The prevalence index method was used to categorise the species into wetland and non-wetland indicators. Log series and Hill number models were applied to quantify community assemblages, whereas the CCA technique was used to examine the relationship between anthropogenic activities and species presence or absence. In all, 2 185 individuals, belonging to 32 families and 68 species were recorded.<em> Paspalum orbiculare</em> and <em>Persicaria lanigera</em> were the most abundant, indicating their wide distribution. Mean number of individuals were highest at Atafua and lowest at Owabi. An abundance of terrestrial species (41.2%; i.e. plant species not listed as obligate wetland plants) and facultative species (30.9%), compared with obligate wetland species (27.9%), suggests a dominance of species from dryland habitats into the wetland. Farming activities, increased levels of NH<sub>4</sub><sup>+</sup>, PO<sub>4</sub><sup>3+</sup> and NO<sub>3</sub>–N, were the predictors that explained 72.01% of the overall variability in community assemblages. The results revealed the impact of the anthropogenic activities on the ecological integrity of the Owabi Ramsar Wetland and the need to institute conservation measures outlined in this study.&nbsp;</p> Collins A Nsor, Rockson Acolatse, John N Mensah, Samuel K Oppong, Daniel Dompreh, Louis Addai-Wireko Copyright (c) https://www.ajol.info/index.php/ajas/article/view/225200 Sat, 14 May 2022 00:00:00 +0000 Comparison of calcium concentration in scales and vertebral column of a cyprinid from calcium-limited environments in the Lake Victoria Basin, Uganda https://www.ajol.info/index.php/ajas/article/view/225201 <p>Despite dramatic differences in calcium concentrations within aquatic systems, very few studies have explored the relationships between ambient calcium concentration and the calcium concentration of resident fish under natural conditions. This study compares calcium concentration in the water to that of the scales and vertebral column of the African cyprinid, <em>Rastrineobola argentea</em> from lakes Nabugabo and Victoria, East Africa. The concentration of calcium in Lake Nabugabo, which averaged 1.50 mg l<sup>−1</sup>, was much lower than the average of literature-derived values for the Ugandan portion of Lake Victoria (6.96 mg l<sup>−1</sup>). <em>Rastrineobola argentea</em> from Lake Victoria were characterised by higher levels of calcium in the scales than that of conspecifics from Lake Nabugabo, whereas<br>there was no difference in vertebral column calcium concentration between the two populations. Within Lake Nabugabo, calcium concentration was lower in the scales than in the vertebral column of <em>R. argentea</em>, whereas no difference was detected between the scalar and vertebral calcium concentrations of conspecifics from Lake Victoria. These results suggest that ambient calcium concentration may affects tissue levels and that fish in Lake Nabugabo may remobilise calcium from their scales to maintain skeletal growth and development.</p> WA Nesbitt, SB Clarke, LJ Chapman Copyright (c) https://www.ajol.info/index.php/ajas/article/view/225201 Sat, 14 May 2022 00:00:00 +0000 Using the Kariba Invitation Tiger Fishing Tournament for monitoring an invasive crayfish Cherax quadricarinatus in Lake Kariba, Zimbabwe https://www.ajol.info/index.php/ajas/article/view/225203 <p>The stomach contents of tigerfish <em>Hydrocynus vittatus</em>, caught in an angling competition on Lake Kariba, were examined to determine the extent to which they feed on the invasive crayfish <em>Cherax quadricarinatus</em>. 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 (<em>Limnothrissa </em><em>miodon</em> (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 <em>Limnothrissa miodon</em> and, more recently, the crayfish, <em>C. quadricarinatus</em>.</p> LT Marufu, C Phiri, M Barson, T Nhiwatiwa Copyright (c) https://www.ajol.info/index.php/ajas/article/view/225203 Sat, 14 May 2022 00:00:00 +0000 <b>Erratum</b>: Quality evaluation of <i>Artemia cysts</i> from three Algerian populations https://www.ajol.info/index.php/ajas/article/view/225204 <p>The <em>p</em>-values were incorrectly represented on pages 466 and 467. The level of statistical significance for ANOVA should be <em>p</em> &lt; <strong>0.05</strong>, not <em>p</em> &lt; 0.5.<br>Specific sentences are corrected as follows:<br><strong>Page 466</strong><br>• 'The results of fatty acid composition, biometry and hatching characteristics were compared between the different populations using ANOVA (<em>p</em> &lt; 0.5).' should read 'The results of fatty acid composition, biometry and hatching characteristics were compared between the different populations using ANOVA (<em>p</em> &lt; 0.05).'<br>• 'The three populations examined exhibit differences in cyst diameters for both decapsulated and hydrated cysts (<em>p</em> &lt; 0.5).' should read 'The three populations examined exhibit differences in cyst diameters for both decapsulated and hydrated cysts (<em>p</em> &lt; <strong>0.05</strong>).'<br>• 'Except for El Melah and Timimoune, decapsulated cyst mean diameter presented no significant differences (<em>p </em>&gt; 0.5).' should read 'Except for El Melah and Timimoune, decapsulated cyst mean diameter presented no significant differences (<em>p</em> &gt; <strong>0.05</strong>).'<br>• 'The Bethioua population was significantly larger than the Timimoune and El Melah populations (<em>p</em> &lt; 0.5).' should read 'The Bethioua population was significantly larger than the Timimoune and El Melah populations (<em>p</em> &lt; <strong>0.05</strong>).'<br>• 'There were no significant differences between the mean size of the nauplii instar-1 from Timimoune and El Melah populations (<em>p</em> &gt; 0.5).' should read 'There were no significant differences between the mean size of the nauplii instar-1 from Timimoune and El Melah populations (<em>p</em> &gt; <strong>0.05</strong>).'<br>• 'The hatching efficiency for decapsulated and non-decapsulated cysts for the Timimoune population and that of both of the Bethioua and El Melah populations were found significantly different (<em>p</em> &lt; 0.5).' should read 'The hatching efficiency for decapsulated and non-decapsulated cysts for the Timimoune population and that of both of the Bethioua and El Melah populations were found significantly different (<em>p</em> &lt; <strong>0.05</strong>).'<br>• 'Table 1: Biometry and hatching characteristics of three Artemia populations from Algeria. Different superscripts in the same row denote significant differences (<em>p</em> &lt; 0.5)' should read 'Table 1: Biometry and hatching characteristics of three Artemia populations from Algeria. Different superscripts in the same row denote significant differences (<em>p</em> &lt; <strong>0.05</strong>)'</p> <p><br><strong>Page 467</strong><br>• 'Table 2: Fatty acids composition (percentage of the total fatty acids from the total lipids) and total identified fatty acids (mg g−1 dry weight) of the cysts from three <em>Artemia</em> populations of Algeria (means and standard deviation, n = 3). HUFA: highly unsaturated fatty acids; n-3 HUFA: ≥20:3n-3; n-6 HUFA: ≥20:2n-6. Different superscripts in the same row denote significant differences (p &lt; 0.5)' should read 'Table 2: Fatty acids composition (percentage of the total fatty acids from the total lipids) and total identified fatty acids (mg g<sup>−1</sup> dry weight) of the cysts from three <em>Artemia</em> populations of Algeria (means and standard deviation,<br>n = 3). HUFA: highly unsaturated fatty acids; n-3 HUFA: ≥20:3n-3; n-6 HUFA: ≥20:2n-6. Different superscripts in the same row denote significant differences (p &lt; 0.05)'</p> <p>• 'Bethioua and El Melah population showed significant differences (p &lt; 0.5) in the percentage of 10 fatty acids (14:1; 16:0; 16:1n-7; 17:0; 18:0; 18:3n-3; 18:4n-3; 20:3n-3; 20:4n-3 and 20:5n-3).' should read 'Bethioua and El Melah population showed significant differences (p &lt; 0.05) in the percentage of 10 fatty acids (14:1; 16:0; 16:1n-7; 17:0; 18:0; 18:3n-3; 18:4n-3; 20:3n-3; 20:4n-3 and 20:5n-3).'</p> <p>• 'There were significant differences between Timimoune and El Melah population (p &lt; 0.5) in the percentage of four fatty acids (15:0, 18:0, 18:1n-7 and 18:2n-6).' should read 'There were significant differences between Timimoune and El Melah population (<em>p</em> &lt; <strong>0.05</strong>) in the percentage of four fatty acids (15:0, 18:0, 18:1n-7 and 18:2n-6).'</p> <p>• 'There were no significant differences (<em>p</em> &gt; 0.5) between the Bethioua and Timimoune population in fatty acid composition.' should read 'There were no Significant differences (<em>p</em> &gt; <strong>0.05</strong>) between the Bethioua and Timimoune population in fatty acid composition.'</p> C Chabet Dis, W Refes, I Varó, F Hontoria, F Amat, JC Navarro Copyright (c) https://www.ajol.info/index.php/ajas/article/view/225204 Sat, 14 May 2022 00:00:00 +0000