Browsing by Author "Christison, Kevin"

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    Epizootic ulcerative syndrome – first report of evidence from South Africa's largest and premier conservation area, the Kruger National Park
    (ScienceDirect, 2019) Christison, Kevin
    This study reports on the first evidence of genomic material of the causative agent for epizootic ulcerative syndrome (EUS), Aphanomyces invadans, from fish in the Limpopo River system and the Kruger National Park, South Africa. Fourteen fish species were collected from various depressions in the floodplains of the Limpopo and Luvuvhu Rivers in the Makuleke Wetlands during 2015 and 2017.
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    The potential of commercial praziquantel formulations as "off label" treatments for diplectanum oliveri (monogenea) infecting cultured argyrosomus species in the South African marine finfish aquaculture industry
    (University of the Western Cape, 2012) Joubert, Casper Jan Hendrik; Christison, Kevin; Kaiser, Horst
    Aquaculture is a vast industry all over the world and has increased significantly during the past 30 years. In South Africa, finfish aquaculture farms stretch from Gansbaai to as far as Richards bay with the potential of extending into Mozambique. The future success of this fast growing industry in South Africa strongly relies on the development of the supporting sector such as government legislation, sponsorship, participation of the pharmaceutical industry and research and development in aquatic organism health management. Diplectanum oliveri Williams, 1989, a monogenean gill parasite of both Argyrosomus japonicus (Temminck & Schlegel, 1843) (dusky kob) and A. inodorus Griffiths & Heemstra, 1995 (silver kob) is currently regarded in South Africa as the most persistent ectoparasite associated with the culture of both fish species, causing pathological tissue changes in the areas associated with attachment and feeding which can result in stock losses. The egg production of D. oliveri was used to evaluate and develop a method to quantify monogenean infections on fish, by counting the eggs produced by infra-populations of these parasites over a 24-hour period and to determine the reliability of this method as a non-invasive/non-destructive method to quantify the intensity of an individual infra-population of parasites on a single host. Currently, Diplectanum spp. on dusky kob are being controlled in local mariculture facilities using methods and drugs that are traditionally used for monogeneans (flukes) and are regarded as effective. Most of these drugs are, however, no longer approved for use in food fish and none of them has proven to be very effective in controlling D. oliveri in culture facilities, which can result in subsequent re-infections of epidemic proportion. Currently, there are no anthelmintics registered for aquaculture in South Africa. An registered anthelmintic used in terrestrial animals (sheep, goats, cattle and ostriches) containing praziquantel was tested at various concentrations and exposures against D. oliveri on A. japonicus to determine the efficacy of two different formulations and the potential for "off label" use. The 20 ppm (high) praziquantel concentration treatments eliminated all adult parasites, but caused significant measureable stress and affected the central nervous system of the fish, which resulted in death of all fish in the solution group after 18 hours. The 2 ppm (low) concentrations failed to remove all adult parasites. Although both the 2 hour (short) exposure/high concentration and 24 hour (long) exposure/low concentration of the suspension formulation were effective, but only the short exposure/high concentration eliminated all adult parasites with little change in behaviour by the treated fish.
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    Risk analysis and potential implications of exotic Gyrodactylus species on cultured and wild cyprinids in the Western Cape, South Africa
    (University of the Western Cape, 2010) Maseng, Monique Rochelle; Christison, Kevin; Griffiths, Charles; Faculty of Science
    The expansion of the South African aquaculture industry coupled with the lack of effective parasite management strategies may potentially have negative effects on both the freshwater biodiversity and economics of the aquaculture sector. Koi and goldfish are notorious for the propagation of parasites worldwide, some of which have already infected indigenous fish in South Africa. Koi and goldfish have been released into rivers in South Africa since the 1800’s for food and sport fish and have since spread extensively. These fish are present in most of the river systems in South Africa and pose an additional threat the indigenous cyprinids in the Western Cape. Monogenean parasites of the genus Gyrodactylus are of particular concern, as their unique biology renders them a possible threat. Gyrodactylus kherulensis and G. kobayashii were identified from koi and goldfish respectively imported from Asia, Europe and locally bred fish. Morphometrics and the use of statistical classifiers, which includes univariate (ANOVA and Kruskal-Wallis), bivariate (Pearson’s correlation) and multivariate (Principal Component Analysis) placed the two species within their respective groups. There was some intraspecific variation among the different populations collected from the various locations, especially in the hamulus and ventral bar features, but the marginal hooklets, however, remained static for both helminth species. This illustrates again the importance of the minor variations in the marginal hook features in gyrodactylid taxonomy. Infection trials conducted by co-habitation of infected koi and goldfish with two indigenous redfin minnow species, Pseudobarbus burchelli and P. phlegethon showed that both G. kherulensis and G. kobayashii could successfully transfer and establish themselves on P. phlegethon, where the infection increased rapidly initially, but remained relatively constant thereafter. P. burchelli appeared to be inherently resistant as the parasite population growth rate initially remained steady, until the infection died off. The wild-caught indigenous fish were however not infected with any exotic Gyrodactylus species, but a new species, G. burchelli n. sp. described from the body surfaces of P. burchelli.