OALib Journal期刊

ISSN: 2333-9721




2016 ( 1 )

2015 ( 39 )

2014 ( 57 )

2013 ( 79 )


匹配條件: “Wilmien Luus-Powell” ,找到相關結果約708條。
Surface morphology of the fish parasite Chonopeltis victori Avenant- Oldewage, 1991 and aspects of the histomorphology
Wilmien J Luus-Powell,Annemarie Avenant-Oldewage
Koedoe : African Protected Area Conservation and Science , 1996, DOI: 10.4102/koedoe.v39i1.282
Abstract: The ultrastructure and aspects of the histomorphology of Chonopeltis victori, parasitic on Labeo rosae, L. congoro, L. ruddi, L. cylindricus and Barbus marequensis, are described from scanning electron micrographs and transverse sections. Chonopeltis victori is characterised by sharply pointed tips of the abdomen which are directed outward. Sexual dimorphism is particularly evident from the structure of the natatory lobes on the fourth swimming legs and the accessory copulatory structures on the second, third and fourth swimming legs of males. The most striking feature on leg four of the male is the peg. The elevated peg appears tubular, but the sides are not fused. On the inner collar elliptical projections, each with a central, circular pore, are present. On the elongated outer collar small indentions occur peripherally. The dorsal surface of the peg is subterminally covered by elongated scales. The ventral surface of the thorax and swimming legs are covered with different shapes of posteriorly directed scales. Interspersed amongst these scales, as well as on the dorsal surface, eight types of setae are present in large numbers. The possible function of the peg and other structures are described.
The occurrence of metazoan endoparasites of Schilbe intermedius Rüppell, 1832 from the Nwanedi-Luphephe Dams of the Limpopo River System, South Africa
W.J. Smit,Wilmien Luus-Powell
African Zoology , 2012,
Abstract: The present study deals with the survey of endoparasites from Schilbe intermedius (Silver catfish) at the Nwanedi-Luphephe Dams from July 2009 to May 2010. The hosts (n = 60) were collected using gill nets and examined for endoparasites. The following parasites were recorded: three species of trematodes, i.e., Clinostomum metacercariae in the body cavity (prevalence 40%), an unidentified adult digenean in the small intestine (prevalence 33.3%) and Diplostomum metacercariae from the eye (prevalence 1.7%); two species of nematodes, i.e., Contracaecum larvae in the body cavity (prevalence 95%) and Paracamallanus cyathopharynx from the intestine (prevalence 63.3%). None of the fish examined during this study were in a notably poor state of health due to parasitism. Correlations between endoparasite infection and host size, as well as seasonal variation in their infection dynamics associated with environmental changes, were detected.
Pentastomid parasites in fish in the Olifants and Incomati River systems, South Africa
Wilmien J. Luus-Powell,Antoinette Jooste,Kerstin Junker
Onderstepoort Journal of Veterinary Research , 2010, DOI: 10.4102/ojvr.v75i4.108
Abstract: During parasitological field surveys of freshwater fish, sebekiid and subtriquetrid pentastome larvae were recovered from the body cavity or swim bladder of several fish species from various localities in Limpopo and Mpumalanga Provinces, South Africa. Sebekia wedli was recovered from the body cavity of Marcusenius macrolepidotus (Mormyridae) from Flag Boshielo Dam, Limpopo Province, and Alofia sp. and Subtriquetra rileyi were found in the swim bladder of Oreochromis mossambicus (Cichlidae) from the Phalaborwa Barrage, Limpopo Province. The latter species was also collected from the swim bladder of O. mossambicus in dams in the Phalaborwa region and the Ga-Selati River, Limpopo Province. A single specimen of Sebekia okavangoensis was present in the body cavity of Clarias gariepinus (Clariidae) in a dam on a sugarcane farm in the Komatipoort region, Mpumalanga Province. Pentastomid infections in the Mormyridae and Clariidae represent new host records.
Report on some monogenean and clinostomid infestations of freshwater fish and waterbird hosts in Middle Letaba Dam, Limpopo Province, South Africa
P.A.S. Olivier,Wilmien J. Luus-Powell,J.E. Saayman
Onderstepoort Journal of Veterinary Research , 2010, DOI: 10.4102/ojvr.v76i2.44
Abstract: This report deals with the results of a parasitological study done as part of a post-impoundment ecological study of Middle Letaba Dam, Limpopo Province, South Africa. It involved a seasonal survey protocol with particular attention to the diversity and prevalence of the parasitic fauna of the indigenous fish community of the dam and the role of selected fish-eating birds in the life cycle and distribution of fish helminths. The potential species composition of fish of the dam is provided. Monogenean and clinostomatid parasites encountered are listed and infestation statistics of fish and fish-eating bird hosts are presented. The results of this study also provide information on new distribution and host records of the encountered monogeneans.
Diversity of metazoan parasites of the Mozambique tilapia, Oreochromis mossambicus (Peters, 1852), as indicators of pollution in the Limpopo and Olifants River systems
Grace N. Madanire-Moyo,Wilmien J. Luus-Powell,Pieter A. Olivier
Onderstepoort Journal of Veterinary Research , 2012, DOI: 10.4102/ojvr.v79i1.362
Abstract: Aquatic systems are affected by a variety of anthropogenic activities that decrease water quality through the introduction of organic and inorganic pollutants. To investigate the relationship between fish parasite communities and water quality, metazoan parasites were examined in 140 specimens of the Mozambique tilapia (Oreochromis mossambicus) sampled in three lakes in the Limpopo Province, namely the Luphephe–Nwanedi Dams (regarded as unpolluted), the Flag Boshielo Dam (regarded as moderately polluted) and a return water dam on a mine site (regarded as polluted). The monogenean parasites Cichlidogyrus halli, digenean larval stages of Clinostomum and Diplostomum spp. and a gryporynchid cestode were found in or on O. mossambicus in all the sampled sites. The distribution of monogeneans (Cichlidogyrus sclerosus, Cichlidogyrus dossoui, Cichlidogyrus tilapiae, Scutogyrus longicornis and three Enterogyrus spp.), metacercarial stages of two digeneans (Neascus and Acanthostomum spp.) and nematodes (an unidentified nematode, Contracaecum sp., Paracamallanus cyathopharynx and Procamallanus laevionchus) was limited to the unpolluted and moderately polluted lakes. Larval stages of Diplostomum sp. were present in O. mossambicus collected from the unpolluted and polluted sites. The variability of the calculated infection indices (prevalence, mean abundance and mean intensity) and the parameters of species richness and diversity suggest that the structure of parasite communities are affected by the pollution levels of the water. The unpolluted reference site had the highest species richness and the highest overall parasite abundance values. How to cite this article: Madanire-Moyo, G.N., Luus-Powell, W.J. & Olivier, P.A., 2012, ‘Diversity of metazoan parasites of the Mozambique tilapia, Oreochromis mossambicus (Peters, 1852), as indicators of pollution in the Limpopo and Olifants River systems’, Onderstepoort Journal of Veterinary Research 79(1), Art. #362, 9 pages. http://dx.doi.org/10.4102/ojvr.v79i1.362
Ecology of metazoan parasites of Clarias gariepinus (Osteichthyes: Clariidae) from the Nwanedi-Luphephe Dams of the Limpopo River System, South Africa
G.N. Madanire-Moyo,W.J. Luus-Powell,P.A.S. Olivier
African Zoology , 2011,
Abstract: A total of 7748 parasites, belonging to 17 metazoan species, was recorded from 45 specimens of Clarias gariepinus (Burchell, 1822) caught from the Nwanedi-Luphephe Dams, Limpopo River System, South Africa. All host specimens were parasitized by one or more metazoan parasite species. The parasite species included five monogeneans (Gyrodactylus rysavyi,Macrogyrodactylus clarii, Macrogyrodactylus congolensis, Quadriacanthus clariadis andQ. aegypticus), four digeneans (Diplostomum type 3, Tetracotyle sp. metacercaria,
Comparison of IDP and LJ Optimization Procedure for Establishing the Optimal Control of a Nonisothermal Fedbatch Reactor
Rein Luus
Bioautomation , 2009,
Abstract: Optimal control of a nonisothermal fedbatch reactor with heat removal constraint is used as a test problem for comparing iterative dynamic programming (IDP) and Luus- Jaakola (LJ) optimization procedure. Although there are only two control variables, the feed rate and the temperature, the heat production rate constraint makes the optimal control problem very difficult. Therefore, the problem is reformulated by using rate of heat production instead of temperature as the second control variable. To parametrize the optimal control problem, the time interval is divided into P time stages of constant length, and piecewise constant control is used at each time stage. For small values of P , both optimization procedures are almost equivalent. However, when is increased beyond 20, IDP becomes more efficient.
Transmission scheduling for wireless mesh networks with temporal reuse
Luus Francois,Maharaj Bodhaswar
EURASIP Journal on Wireless Communications and Networking , 2011,
Abstract: Link-assigned transmission schedules with timeslot reuse by multiple links in both the space and time domains are investigated in this study for stationary multihop wireless mesh networks with both rate and power adaptivity. Specifically, cross-layer optimised schedules with proportionally fair end-to-end flow rates and network coding capability are constructed for networks operating under the physical interference model with single-path minimum hop routing. Extending transmission rights in a link-assigned schedule allows for network coding and temporal reuse, which increases timeslot usage efficiency when a scheduled link experiences packet depletion. The schedules that suffer from packet depletion are characterised, and a generic temporal reuse-aware achievable rate region is derived. Extensive computational experiments show improved schedule capacity, quality of service, power efficiency and benefit from network coding accrued with schedules optimised in the proposed temporal reuse-aware convex rate region.
Towards a Sociology of Trust: Community Care and Managing Diversity  [PDF]
Jason L. Powell
Sociology Mind (SM) , 2011, DOI: 10.4236/sm.2011.12003
Abstract: The paper is a critical review of the problems and implications of managing diversity in the British community care system. It is a system in need of strong diversity management in the light of the world economic downturn in recent years. Despite raft of policies on leadership in social care in the UK, the structural issues for why the needs of diverse groups are not met are difficult to understand at particular levels of analysis. The central problem has been lack of ‘trust’.
"Close Encounters of the Third Kind" Volunteering,Infrastructure and Governance  [PDF]
Jason L. Powell
Sociology Mind (SM) , 2011, DOI: 10.4236/sm.2011.14028
Abstract: This paper explores the relationship between voluntary sector and governance using England as a case study. One of the key issues in recent times is how voluntary organizations sustain themselves. Although the spate of studies have undoubtedly advanced the state of knowledge about voluntary organisations, we still know very little about the internal composition and operation of volunteer organisations and even less about the way in which internal factors interact within the external world. This research article assesses the factors such as governance and quality, leadership, workforce, performance, partnerships and finance and funding. These different critical success factors are part of the inter-locking infrastructure tools of voluntary organizations that keeps them sustained.

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