African Journal of Aquatic Science最新文献

{"title":"Validation of growth zone formation in Oreochromis mossambicus otoliths collected from an irrigation pond in the Sundays River Valley, Eastern Cape, South Africa","authors":"L. Mofu, T. Dalu, R. Wasserman, D. Woodford, O. Weyl","doi":"10.2989/16085914.2022.2147131","DOIUrl":"https://doi.org/10.2989/16085914.2022.2147131","url":null,"abstract":"In fisheries science, life-history trait information is widely used to estimate fish population recruitment, growth, and mortality. The aging and growth of Oreochromis mossambicus from the Sundays River Valley irrigation pond in the Eastern Cape province of South Africa were determined using otoliths. Mark recapture of chemically-tagged wild fish was used to confirm the periodicity of growth zone creation. A total of 150 specimens of O. mossambicus were obtained using a combination of seine and fyke nets. Female total lengths (Lt ) ranged from 20 to 340 mm, while male Lt ranged from 82 to 374 mm. Growth zone deposition rates of wild O. mossambicus otoliths fluorochrome-marked with oxytetracycline hydrochloride (OTC) and recaptured after one year was consistent with the deposition of one growth increment annually. According to the three-parameter von Bertalanffy model, growth was described using different coefficients for females and males, respectively. The maximum age estimate for both females and males was 12 years. Oreochromis mossambicus in this warm temperate pond had relatively long life spans compared to subtropical populations, which suggest likely long-term population persistence within cooler, novel environments.","PeriodicalId":7864,"journal":{"name":"African Journal of Aquatic Science","volume":"48 1","pages":"105 - 109"},"PeriodicalIF":1.4,"publicationDate":"2023-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43516272","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"New host and distribution records for five species of Enterogyrus Paperna, 1963 (Dactylogyridae: Ancyrocephalinae) from cichlid hosts in South Africa","authors":"I. Přikrylová, S. Tavakol, Nico J. Smit, W. Smit, W. Luus‐Powell","doi":"10.2989/16085914.2022.2142507","DOIUrl":"https://doi.org/10.2989/16085914.2022.2142507","url":null,"abstract":"Between March 2015 and September 2016, three species of Cichlidae (Coptodon rendalli, Oreochromis mossambicus and Tilapia sparrmanii) were screened for the presence of stomach monogeneans. Four localities across three provinces of South Africa (Limpopo, Northern Cape and North West) were sampled and a total of five Enterogyrus species were identified, viz. E. cichlidarum, E. coronatus, E. malmbergi, E. mashegoi and E. multispiralis. Finding E. malmbergi from O. mossambicus and T. sparrmanii represents new host and geographic records. Enterogyrus coronatus was reported from C. rendalli and T. sparrmanii from three localities. Both hosts are new host records for the species and show a wide distribution of E. coronatus within South Africa. Tilapia sparrmanii is a new host record for E. cichlidarum, E. mashegoi and E. multispiralis. Enterogyrus mashegoi and E. cichlidarum are reported from new localities.","PeriodicalId":7864,"journal":{"name":"African Journal of Aquatic Science","volume":"48 1","pages":"110 - 114"},"PeriodicalIF":1.4,"publicationDate":"2022-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47609055","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Molluscicidal and cercaricidal effects of Persicaria senegalensis on Radix natalensis snails and their echinostome-shed cercariae in South Africa","authors":"M. Mathole, P. King","doi":"10.2989/16085914.2022.2142506","DOIUrl":"https://doi.org/10.2989/16085914.2022.2142506","url":null,"abstract":"Persicaria senegalensis is an aquatic plant of the Family Polygonaceae with apparent molluscicidal properties. The research evaluated the molluscicidal effect of P. senegalensis on the freshwater snail Radix natalensis, and its echinostome-shed cercariae. Various compounds from Persicaria senegalensis were extracted and qualitatively analysed. Radix natalensis and the cercariae were exposed to different extract concentrations of P. senegalensis and tested for a period of 24 and 3.5 hours, respectively. Glycosides, saponins, tannins and phenols were found to be present in the leaf, flower and stem extracts. The roots only contained saponins, with traces of tannins and phenols. Terpenoids were absent in the plant. The LC50 values of P. senegalensis extracts against R. natalensis were determined at 18.20 ± 14.78, 30.90 ± 31.25, 42.66 ± 55.67 and 77.62 ± 132.31 for leaves, flowers, stems, and roots respectively. For the cercaricidal activities of leaf, flower, stem and root extracts, the LC50 values against R. natalensis-shed cercariae were 20.89 ± 8.91, 30.90 ± 22.10, 42.66 ± 40.94 and 77.62 ± 93.62, respectively. The mortality rate of tested organisms increased with increased concentrations. It is concluded that extracts of P. senegalensis have molluscicidal and cercaricidal properties; and, therefore, has potential as an alternative biological control agent for freshwater snails, their cercariae and, subsequently, other snail-transmitted parasitic diseases.","PeriodicalId":7864,"journal":{"name":"African Journal of Aquatic Science","volume":"48 1","pages":"71 - 76"},"PeriodicalIF":1.4,"publicationDate":"2022-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49276624","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Restoration of South African estuaries: successes, failures and the way forward","authors":"L. Claassens, J. Adams, NM de Villiers, J. Wasserman, A. Whitfield","doi":"10.2989/16085914.2022.2115970","DOIUrl":"https://doi.org/10.2989/16085914.2022.2115970","url":null,"abstract":"Major threats to South African estuaries include freshwater flow alterations, urbanisation, habitat transformation, deteriorating water quality, increased biological invasions and resource over-exploitation. Although South African estuary restoration is in its infancy, important lessons have been learnt through past efforts undertaken in some of the most impacted systems. This review presents case studies focused on hydrological and physical restoration actions, while recognizing the need to implement urgent remedial measures to restore the populations of targeted estuary-associated marine fish species. Common interventions designed to arrest declining estuary health include artificial management of estuary mouths and the use of artificial structures to restore tidal action and remediate erosion damage. Limited natural habitat restoration actions have been conducted on the subcontinent. Fortunately, estuaries are resilient ecosystems and can recover fairly rapidly if appropriate restoration interventions are successfully applied. Restoration needs to be co-ordinated through a national strategy which is currently not in place. It is particularly important to address the root cause of deterioration through active restoration and/or rehabilitation measures rather than only managing symptoms. The implementation of existing and future conservation legislation regarding the exploitation of natural resources within estuaries needs to be prioritised, so that over-exploited angling and subsistence fish species populations can recover.","PeriodicalId":7864,"journal":{"name":"African Journal of Aquatic Science","volume":"48 1","pages":"1 - 18"},"PeriodicalIF":1.4,"publicationDate":"2022-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42521502","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Zooplankton distribution and community structure as a function of environmental variables in the Niger River and its tributaries in Niger","authors":"H. Souley Adamou, B. Alhou, M. Tackx, F. Azémar","doi":"10.2989/16085914.2022.2122391","DOIUrl":"https://doi.org/10.2989/16085914.2022.2122391","url":null,"abstract":"The Niger River and its main tributaries (Sirba, Tapoa and Mékrou) in Niger were sampled during high and low water flow with the objectives of (1) comparing the taxonomic structure, diversity and abundance of the zooplankton community (rotifers, copepods, crustaceans) along the river and (2) determining which environmental or biological factors influence the distribution of the zooplankton communities most strongly. The impact of the tributaries at high-flow was also evaluated. Rotifers (32 taxa) were the most abundant and diverse followed by Cladocerans (13 taxa) and Copepods (three taxa). The mean number of taxa (16.5 and 17.6, respectively), the Shannon-Weaver diversity index (2.7 and 2.8, respectively) and the evenness (0.7 and 0.7, respectively) did not vary significantly between the high- or low-flow periods, or along the length of the Niger River and its tributaries. The mean zooplankton abundance was highest during low-flow periods (40 × 103 ± 45 × 103 ind. m−3) but showed no specific spatial pattern. During high-flow sampling, the mean zooplankton abundance (3 × 103 ± 2 × 103 ind. m–3) increased progressively downstream. RDA analysis showed that rotifers are associated with high conductivity and NO2 − concentrations, copepods with chlorophyll a, while cladocerans were abundant when conductivity, chlorophyll a and NO2 − concentrations were low.","PeriodicalId":7864,"journal":{"name":"African Journal of Aquatic Science","volume":"48 1","pages":"49 - 63"},"PeriodicalIF":1.4,"publicationDate":"2022-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69845716","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Water quality of the Blue Nile at Khartoum, Sudan, before complete filling of the Grand Ethiopian Renaissance Dam","authors":"Amh Bashir, ME Abdelrahman, F. Sinada","doi":"10.2989/16085914.2022.2123304","DOIUrl":"https://doi.org/10.2989/16085914.2022.2123304","url":null,"abstract":"Physico-chemical variables were monitored biweekly for the Blue Nile at Khartoum between July 2017–June 2019. The aim was to document the present status of water quality at Khartoum before complete filling of the Grand Ethiopian Renaissance Dam (GERD). Physico-chemical parameters within acceptable limits recommended by WHO for drinking water included pH (7.2–10.8), temperature (13.7–30.4 °C), conductivity (137–281 μS cm−1), total dissolved solids (75–141 mg l−1), total residue (5–3194 mg l−1), alkalinity (93–176 mg CaCO3 l−1), dissolved oxygen (3.5–10.9 mg l−1), nitrite–nitrogen (<detection limit (DL)−43 µg l−1), ammonium–nitrogen (<DL−940 µg l−1), nitrate– nitrogen (<DL−1468 µg l−1), phosphate–phosphorus (<DL−63 µg l−1), silica (4.0–23.6 mg l−1), iron (<DL−250 µg l−1) sodium (3.2–15.7 mg l−1), potassium (0.7–5.6 mg l−1), calcium (6.2–30.3 mg l−1), and magnesium (1.5–11.5 mg l−1). Total residue and pH were amongst the measured variables that were outside of the WHO recommendations. This study revealed that the Blue Nile remains generally unpolluted, and has not been significantly negatively affected by runoff from urbanisation or sewage contamination. This study presents further evidence that industrial wastes discharged upstream of Khartoum have not accumulated downstream as they are carried into the Main Nile by the annual floodwater pulses. The water is therefore currently suitable for drinking and all other uses. However, accumulation of pollutants in the Blue Nile may be problematic once filling of the GERD is complete as the discharge during flooding events necessary to flush the river will be reduced.","PeriodicalId":7864,"journal":{"name":"African Journal of Aquatic Science","volume":"48 1","pages":"28 - 48"},"PeriodicalIF":1.4,"publicationDate":"2022-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47265052","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Southern mullets (Chelon richardsonii) as a potential biological indicator for mercury pollution in the Walvis Bay lagoon, Namibia","authors":"V. K. Kapula, H. Ndjaula, Stephanus Hamutenya, J. Iitembu","doi":"10.2989/16085914.2022.2128292","DOIUrl":"https://doi.org/10.2989/16085914.2022.2128292","url":null,"abstract":"Southern mullet Chelon richardsonii is one of the important fish species found in the Walvis Bay lagoon (WBL) that is commercially exploited for local consumption. The southern mullet is, however, exposed to mercury (Hg) found in sediments, which forms part of its diet. This study evaluated the Hg concentration in muscles, stomach content, liver, and gills of C. richardsonii over two years. The Hg concentration was higher in the liver (0.005 mg kg−1) and relatively lower in the gills (0.001 mg kg−1). There were temporal variations in Hg concentration among the tissues; a positive correlation between mean Hg concentration and fish sizes (total length and total weight) was documented in the gills; and a negative correlation for size versus Hg concentration was recorded in the livers, stomach contents, and the muscles of southern mullets. The Hg concentrations of all tissues were below the World Health Organisation (WHO) limit for fish (0.5 mg kg−1), which indicates that it does not pose a human health risk at the current levels. This study’s findings form a baseline for using southern mullets as biological indicators of Hg pollution in WBL. The study also highlights the need for regular monitoring programmes to protect and maintain the ecological characteristics of WBL as per Namibia’s mandates under the Ramsar Convention.","PeriodicalId":7864,"journal":{"name":"African Journal of Aquatic Science","volume":"48 1","pages":"77 - 83"},"PeriodicalIF":1.4,"publicationDate":"2022-11-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41312647","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"An assessment of water and sediment quality of aquatic ecosystems within South Africa’s largest floodplain","authors":"D. van Rooyen, R. Gerber, N. Smit, V. Wepener","doi":"10.2989/16085914.2022.2124946","DOIUrl":"https://doi.org/10.2989/16085914.2022.2124946","url":null,"abstract":"Ndumo Game Reserve (NGR), a Ramsar site, situated in South Africa’s largest floodplain (Phongolo River floodplain) in northern KwaZulu-Natal, with important aquatic ecosystems: the Usuthu and Phongolo rivers and their associated floodplain lakes. While the Phongolo River is regulated, the Usuthu River is unregulated and subjected to fewer anthropogenic activities that influence the downstream environmental quality of this Ramsar system. The present study evaluates the environmental quality of floodplain systems in the NGR. Water and sediment were sampled and analysed from both rivers and associated floodplain lakes during different hydrological periods (flow). Using multivariate statistical techniques, ionic compositions, as well as water and sediment quality indices of the ecosystems were evaluated. Key findings suggest spatial and flow-related differences, which highlight the human-driven impacts from the upper catchments and the rivers influence on their respective floodplain lakes. The environmental quality (water and sediments) could be classified as ‘good’ and predominantly unimpacted. Notably, ionic composition of river water showed the importance of the unregulated Usuthu River and its contribution to aquatic ecosystems within the NGR and their continued functioning. The quality indices further indicated that metals do not currently pose any ecological risks to these systems.","PeriodicalId":7864,"journal":{"name":"African Journal of Aquatic Science","volume":"47 1","pages":"474 - 488"},"PeriodicalIF":1.4,"publicationDate":"2022-10-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46260514","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Perspectives on Protecting African freshwater Ecosystems in the Anthropocene","authors":"J. King, C. Palmer","doi":"10.2989/16085914.2022.2132045","DOIUrl":"https://doi.org/10.2989/16085914.2022.2132045","url":null,"abstract":"Our announcement of this Special Medal Issue in 2020 outlined the growing and urgent concern for the state of Earth’s inland waters, and called on authors to submit papers that would address one or more of the following topics and, importantly, links between them: • water quantity: flow, inundation, groundwater recharge • water quality: dissolved and particulate matter, temperature • sediments, geomorphic structure, hydraulics: load, extraction, channel form and function, habitats • freshwater species: natural community structure, life cycles, exploitation, poaching • non-native species: invasions, habitat destruction, imbalance, escalation to pest proportions • connectivity: the movement of water, sediments and biota • livelihoods: social and cultural dependence on freshwater ecosystems • governance: socio-economic drivers of degradation, balancing the three pillars of sustainable development (social equity, ecological integrity, economic wealth). We sought papers from freshwater, resource economic and social scientists; water managers; governments; legislators; and other relevant specialists, encouraging co-authorship from more than one discipline in order to move closer to the realities of managing water ecosystems and addressing the requirements of their users. We hoped for information on the collaboration between disciplines, the use of knowledge as well as data, and how technical information can be conveyed in a form accessible to a wide range of stakeholders. The call for papers resulted in submission of papers from across southern Africa. Several of these did not address the science-management interface in any formal way and, because they had considerable merit, were referred to one of the scheduled issues of AJAS. The papers presented in the Special Medal Issue all have a link through to management, albeit stronger in some cases than in others. They progress our thinking regarding the management and sustainable use of freshwater ecosystem, but do they go far enough? We will return to this later. The papers have been arranged in three themes: freshwater ecosystem stressors; river basin and freshwater ecosystem management; and a case study. freshwater ecosystem stressors","PeriodicalId":7864,"journal":{"name":"African Journal of Aquatic Science","volume":"47 1","pages":"iii - vi"},"PeriodicalIF":1.4,"publicationDate":"2022-10-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49526351","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The application of Bayesian networks to evaluate risks from multiple stressors to water quality of freshwater ecosystems","authors":"V. Wepener, G. O’Brien","doi":"10.2989/16085914.2022.2130866","DOIUrl":"https://doi.org/10.2989/16085914.2022.2130866","url":null,"abstract":"It is difficult to predict and manage the ecological consequences of multiple water quality stressors on our freshwater systems. This is due to the dynamism of the source-stressor-response relationships and multiple factors including lack of data, complex impact pathways and risks, and uncertainties that are difficult to parameterise. We present a risk-based probability modelling approach using a Bayesian network (BN), to manage multiple water quality stressors at multiple spatial scales. We illustrate the use of this approach, by evaluating the probable ecological effects of altered water quality associated with multiple sources in three case study rivers in South Africa. Water quality and land use activity were used to describe conceptual risk pathways, parameterise the BNs and model the probable consequences of multiple water quality stressors. The BN model demonstrated that the endpoints that were selected for the study reflected the risks associated with the levels of the input water quality variables. The model further demonstrated that the electrical conductivity BN was just as sensitive as the more complex salt model. The BN model was further able to accurately represent risks to all systems irrespective the water quality data base size. This approach can contribute towards more sustainable water resource management.","PeriodicalId":7864,"journal":{"name":"African Journal of Aquatic Science","volume":"47 1","pages":"231 - 244"},"PeriodicalIF":1.4,"publicationDate":"2022-10-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41990402","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}