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The biodiversity, systematics and ecology of fish parasitic gnathiid isopods from the east coast of South Africa

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dc.contributor.advisor Dr. N.J. Smit Prof. A. Avenant-Oldewage en
dc.contributor.author Hadfield, Kerry Ann
dc.date.accessioned 2009-03-24T12:10:21Z
dc.date.available 2009-03-24T12:10:21Z
dc.date.issued 2009-03-24T12:10:21Z
dc.date.submitted 2007-12
dc.identifier.uri http://hdl.handle.net/10210/2306
dc.description M.Sc. en
dc.description.abstract The larvae of gnathiid isopods are known to parasitise a large variety of intertidal fish worldwide. In South Africa, the larvae of Gnathia africana Barnard, 1914, have been recorded from various intertidal fish hosts along the West and South Coasts. These regions are influenced by the cold waters of the Benguela Current and share similar intertidal fish species. However, the fauna of the East Coast is influenced by the warm waters of the Agulhas Current and the species composition differs dramatically from the South and West Coasts. It was thus hypothesised that the gnathiid species infesting the East Coast intertidal fishes would not be G. africana, but possibly a new species. To test this hypothesis, sampling for gnathiids was done at different times from March 2006 to February 2007, including all four seasons to determine seasonal variation of the infestations. Intertidal fishes were collected using hand held nets and kept in aerated tanks until the gnathiids completed their feeding. Once fed, the gnathiids were kept alive in sample bottles with fresh sea water until moulting occurred. A total of 316 fishes belonging to 17 species were collected. Of these, 15 species were parasitised by gnathiids with a mean of four gnathiids per fish. Although the East Coast gnathiids parasitised a large variety of hosts, the preferred hosts were Scartella emarginata (maned blenny), Antennablennis bifilum (horned rockskipper), and Istiblennius dussumieri (streaky rockskipper) with a prevalence of 89.6%, 77.2% and 74.5% respectively. Light and scanning electron microscopy were used to assist in comparing the characteristics of the East Coast gnathiid to other known gnathiids. Since the taxonomy of gnathiids is based on male morphology, these experiments included the moulting of final stage larvae into adults. Results indicated that all the East Coast intertidal gnathiids were from the same species and are new to science. The descriptions for the male, female and praniza larva were done to ensure identification of all the life stages of this species. Aspects of the ecology of this new gnathiid species were analysed to determine host preference, gnathiid prevalence and intensity, as well as the possible correlation between the host size and gnathiid abundance. Univariate and multivariate statistical tests (CANOCO and SPSS packages respectively), were used to analyse the data sets Abstract - 13 - collected during the four seasons. The three preferred hosts had the highest prevalences and a positive correlation was detected between host size and gnathiid abundance. Laboratory experiments were also done to elucidate the life cycle and to study the feeding ecology of the East Coast gnathiid. Through life cycle experiments it was determined that the second and third unfed larval stages (zuphea larvae 2 and 3) took an average of 3 h 52 min and 4 h 19 min to feed respectively. After feeding, the second stage fed larvae (praniza 2) took 35 days to moult into the third zuphea form, and the third stage fed larvae (praniza 3) took 38 days to moult into an adult. Male and female praniza 3 larvae moulted into adults approximately 42 and 48 days respectively after their blood meals. Fertilisation occurred within 24 hours after the female had completed her moult. It was thus estimated that the complete life cycle from the first larval stage to adult took between 134 to 140 days in water temperatures ranging between 20°C and 25°C. This is unexpectedly long for gnathiids living in subtropical waters and indicates that water temperature is not always the main factor in determining the duration of gnathiid life cycles. Thus, the hypothesis that a new gnathiid species would be found on the warmer East Coast of South Africa was confirmed. The new Gnathia sp. and all of its life forms were described, analysed using various ecological and statistical techniques, and its life cycle was determined in the laboratory in order to construct a thorough review of this new gnathiid. en
dc.language.iso en en
dc.subject Fishes parasites en
dc.subject Parasites ecology en
dc.subject Isopoda ecology en
dc.title The biodiversity, systematics and ecology of fish parasitic gnathiid isopods from the east coast of South Africa en
dc.type Mini-Dissertation en


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