M.Sc. (Zoology) / The alien fish parasite Argulus japonicus Thiele, 1900 has been introduced to the African subcontinent via exotic fish species. This parasite is now found widely distributed throughout the Transvaal and has assumed near epidemic proportions among fish in the Vaal River system. . Aspects of the reproduction of this parasite were studied. Infected fish from the Vaal River system were maintained in the laboratory in order to establish a stock of A. japonicus. These infected fish, together with Cyprinus carpio Linn. ,1785 from fishponds in Lydenburg, were maintained in a 2125 cubic meter culture tank. This culture of A. japonicus was maintained for more than a year from which specimens were used for experimental work and scanning electron microscopy (SEM). The morphology and anatomy of the sexual organs of both the adult male and female parasites were described. A. japonicus males have thoracic appendages which are functional during copulation. A peg is present on the pre-axial margin of the basis of the fourth thoracic limb and a socket occurs on the dorsal post-axial side of the coxa of the third thoracic limb. The conventional concept concerning copulation is that during copulation the above structures are used only as a clasping mechanism. The peg fits firmly into the socket, keeping the limbs of the male in position, while clasping dorsally round the last thoracic limbs of the female...

M.Sc. / Representatives of the genus Argulus (Crustacea: Branchiura) are ectoparasites of marine, brackish and freshwater fish. A survey of the literature revealed that more than 20 species of the genus are endemic to the African continent. Information on some of the species is extremely meager. Because of a need for a single reference that would present the basic data on the African argulids in a concise and systematic manner, a compendium was compiled of the taxonomic characteristics of all the endemic as well as one alien Argulus species which occur in Africa. The occurrence and distribution of these species are also given. Some discrepancy in terminology was found e.g. in the designation of cephalic appendages, the armature of the carapace, the thoracopods and, in the accessory appendages that are used in copulation. Subsequently, a glossary of technical terms were compiled for the genus Argulus in order that uniform descriptions of morphological structures can be given. Argulid ectoparasites were collected in various impoundments in the Transvaal. All the specimens collected were identified as Argulus japonicus Thiele, 1900. Argulus japonicus affected a broad spectrum of fish hosts. A survey was carried out in Lake Barberspan and Bloemhof Dam in which site selection on hosts was studied and infestation statistics were compiled. The fishlouse A. japonicus is an opportunistic ectoparasite which was probably introduced by introductions of exotic fish. This alien fish parasite was associated with mortalities of rainbow trout, Salmo gairdneri, in an aquaculture system in the Transvaal. A morphological study was carried out on adult, male and female, specimens collected from the Transvaal. This study, the first scanning electron microscopy investigation on any argulid specie as yet, elucidated morphological structures as well as ultrastructures not previously reported.

M.Sc. (Zoology) / Please refer to full text to view abstract

M.Sc. / At present 35 species of Argulus are recognized in Africa. From a summary of the literature available for Argulus species in Africa it is clear that species descriptions are often the only information available for the majority of species. Information on the anatomy and histology of African Argulus species is even more scant. However, previous literature reveals that the anatomy and histology of the digestive system is similar in most branchiurans. The first study includes a description of a poorly known Argulus species described using SEM. Sixteen male and one female specimen of Argulus personatus Cunnington, 1913, were collected from Bathybates ferox Boulenger, 1898, from Lake Tanganyika in northern Zambia. Results from light and scanning electron microscopy (SEM) examinations documented a thickening of cuticle located on the dorsal surface between the last thoracic segment and abdomen, which was rectangular in shape; the pre-oral spine and the proboscis ornamented with simple scales; a set of 3 large simple setae on the distal end of the basal plate; the dorsal distal end of second podomere of the maxillae ornamented with scales resembling those of a fish; the second and third podomeres of maxillae ornamented with two types of pectinate scales (with fine bristle-like ends and scales with large pointed ends); the ventral distal end of third and fourth maxillary podomeres bearing large teardropshaped scales; a pair of tubular structures present adjacent to the anterior projection; a peg on the fourth pairs of legs of males bearing shallow grooves running irregularly across surface; and an accessory cushion bearing minuteprojections. These characters found in A. personatus were addressed in a redescription. The digestive system of Argulus japonicus metanauplii is described following reconstruction from serial sections. The similarities between the larval and adult digestive system are described. Both digestive systems consist of an oesophagus, oesophageal funnel, anterior midgut, midgut enteral diverticula, posterior midgut and a hindgut. Histologically, the foregut of both the adult and larva consist of cuboidal epithelium and both the adult and larval hindguts are composed of columnar epithelium. Despite the similarities between the adults and larvae some differences exist. Differences include that the epithelium lining of the midgut of newly hatched larvae contain yolk. The midgut diverticula are less ramified than in the adult. The posterior midgut is lined with large swollen cuboidal epithelium with large vacuoles and a ciliated border whereas the adult posterior midgut is lined by large papilliform cells. Argulus japonicus larvae only survive a day after hatching without nutrition from a host and once the first stage larvae start to feed on host tissue they feed mainly on epithelial cells and mucus. There was no blood observed in the lumen of the digestive system. It is concluded from the study that much work remains concerning the taxonomy of African species. Many of the species remains inadequately described and new identification keys must be created. New environmentally safe treatments should be a focus of future development. Also, many physiological aspects of the argulid digestive system remain unknown and provide another focus of future research. / Prof. A. Avenant- Oldewage

Submitted by Alberto Vieira (martins_vieira@ibest.com.br) on 2017-09-15T00:18:08Z No. of bitstreams: 1 200636.pdf: 21081818 bytes, checksum: fb6c2340b4c7c60f07a0826e444f7f95 (MD5) / Made available in DSpace on 2017-09-15T00:18:08Z (GMT). No. of bitstreams: 1 200636.pdf: 21081818 bytes, checksum: fb6c2340b4c7c60f07a0826e444f7f95 (MD5) Previous issue date: 1980 / No presente trabalho, são feitas considerações gerais sobre a sistemática, nomenclatura, distribuição zoogeográfica, relação hospedeiro-parasita, controle e profilaxia, distribuição sazonal dos Argulídeos (Crustacea-Branchiura). Abrange ademais a redescrição de seis espécies, do gênero Argulus Müller, das quais uma assinalada pela primeira vez para a nossa carcinofauna. Acompanha o trabalho 12 pranchas. / Some general considerations are given concerning sistematics, nomenclature, zoogeographical distribution, the parasite-host relation ship of the brazilian argulids (Crustacea-Branchiura). The study embraces six species, three are recorded for the first time for our crustacean fauna. Twelve plates illustrates this work.

Argulus foliaceus (Linnaeus, 1758) is a member of the branchiuran family Argulidae and has a worldwide distribution, causing major economic impacts for freshwater aquacultured fish species worldwide. In the UK, it has economic impacts for both aquaculture and sports fishing industries. Previous studies observed haemorrhagic and inflammatory responses after Argulus infection, which has been taken to support the idea that the parasite secretes chemicals during the feeding process to assist with the ingestion of blood and epithelial tissue. The present study suggests that the blood-feeding ectoparasite of fish, A. foliaceus, may use similar mechanisms for evading host immune responses to those used by sea lice and other haematophagous arthropods. No previous studies have directly investigated the nature of the bioactive compounds / proteins, assumed to be released from these ectoparasites, and which are considered to contribute to feeding processes and host-parasite interactions during infection. Thus, the work described in this thesis was undertaken with the objective of identifying, describing and characterising the secretory components that have previously been suggested to be secreted from glandular cells associated with the feeding appendages of Argulus foliaceus. The current study applied transcriptomic and proteomic techniques in conjunction with in situ methods to investigate known immunomodulatory genes that may serve a function in parasite-host interactions. Overall, the findings of this project have generated considerable additional knowledge concerning the biology of Argulus spp. and have provided a list of proteins that may be used by the parasite to facilitate feeding processes by secreting these active molecules into the host and hence modulating their immune defence mechanisms. This information can be used as a baseline for developing freshwater lice control strategies to help prevent the spread of Argulosis in aquaculture by applying vaccination as means of control using the candidate antigens described in this study to specifically target Argulus spp. Knowledge generated by the work described in this thesis can also contribute to the development of drugs for controlling Argulus or functional components of feed that may serve to protect fish against this parasite. Furthermore, data from this thesis enhances the knowledge of the distribution of toxin/venom or venom-like substances in crustaceans and arthropods in general.

Species of Argulus are macro-, ecto-parasites known to infect a wide variety of fish, but in the UK mainly cause problems in rainbow (Oncorhynchus mykiss) and brown trout (Salmo trutta). Argulus foliaceus is estimated to have caused problems in over 25% of stillwater trout fisheries in the UK. While A. foliaceus does not usually cause high levels of mortality, the parasite affects fish welfare, and also makes fish harder to catch due to morbidity and reduced appetite. This can cause severe economic problems for the fishery, resulting in reduced angler attendance due to poor capture rates and the reduced aesthetic appearance of fish; in the worst-case scenario this can result in the closure of the fishery. Current methods of control include chemical treatment with chemotherapeutant emamectin benzoate (Slice), physical intervention with egg-laying boards which are removed periodically and cleaned in order to reduce the number of parasites hatching into the environment, and the complete draining and liming of the lake to remove all free-living and egg stages of the parasite. While these treatments have all been shown to reduce parasite numbers, none are known to have resulted in permament eradication of the parasite. There is evidence to suggest that A. foliaceus will eventually develop resistance to Slice - the only currently available chemical treatment against the infection - and egg-laying boards and the draining and liming of the lake are both time- and labour-intensive. Previous studies have shown that slow fish turnover is a risk factor with respect to A. foliaceus infections, and with a wide variety of stocking practices occurring in the UK one of the first aims of this project was to determine their impact on the host-parasite dynamics. Mathematical models provide a cost-effective way of examining the impact of such practices, and after a literature review (chapter one), in chapter two a three-compartment mathematical model was adapted for use in the A. foliaceus-trout system. Four generalised stocking methods were then incorporated and analysed, and a minimum threshold host density was found to be necessary to sustain the parasite. Including a function which reduced the capture rate as the parasite burden increased allowed the parasite to survive at a lower host density, as susceptible fish were removed from the water at a slower rate, and attached parasites also remained in the water for longer. This resulted in hysteresis in the model, as the invasion threshold for the parasite remained the same, but once established the parasite became harder to eradicate, requiring significant reductions in the host density. In chapter three the model was further developed in order to improve its biological real- ism. Several features were added and these included: natural host mortalities, a separate compartment for the parasite egg population, and parasite survival after the natural or parasite-induced mortality of its host. In chapter four seasonality was added by incorporating temperature-dependent egg-laying rates and an over-wintering period during which the parasite was unable to reproduce. The model was then fit to the available data, and estimates for the rate of parasite-induced host mortalities and the parasite’s rate of attachment to a host were found. In chapter five we returned to stocking methods, this time looking at the frequency and timing of stocking events and the impact of imposing a rod limit (whereby anglers are only permitted to capture four fish per visit); it was concluded that while current guidelines suggest that very frequent trickle stocking is recommended when dealing with Argulus spp. infections, monthly stocking does not appear to worsen the infection, and if the fish capture rate is high then less-frequent stocking may also be permissable - particularly if stocking occurs towards the end of the year when the parasite is no longer active. This practice may, however, be detrimental to the fishery due to low fish densities in the summer months. In chapter six treatment with Slice was included in the model, and it was demonstrated that with constant treatment, and in the absence of reservoir hosts and a withdrawal period from the drug prior to stocking treated fish into the fishery, the parasite was eradicated. Under current veterinary cascade guidelines, however, trout are required to undergo a withdrawal period of 500 degree days prior to being made available for human consumption. When this was included in the model the drug still decreased parasite abundance, but did not eradicate it - this is in agreement with results reported by communications with fishery managers currently treating fish with Slice. A reduction in the withdrawal period of 25% was shown to further decrease parasite abundance, but still did not result in parasite extinction. As constant treatment with Slice is not advisable due to the potential for resistance build-up, we then sought to find time at which to apply a single treatment of Slice, and found that this was in August when the temperature was highest and the parasite was reproducing and attaching to hosts quickly. Egg-laying boards were also incorporated into the model and similarly to findings by Fenton et al. [11] the success of this treatment was mostly dependent on the proportion of eggs being laid on the boards (as opposed to natural substrates). In contrast with the A. coregoni system, however, the boards would have to be cleaned and replaced more frequently that once per year, as several cohorts of A. foliaceus emerge during a single year.