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No description available.

Lernaeocera branchialis (L., 1767) is a parasitic copepod that parasitises a range of gadoids by anchoring in the proximity of the branchial chamber of its host, deriving nutrition from the blood of its host and causing serious pathogenic effects. This study investigates the taxonomy of the juvenile free-swimming stages and host location behaviour in the pre-metamorphosed adult female. The large size and distinctive appearance of the metamorphosed adult female stage, coupled with the wide exploitation and commercial importance of one of its principle final gadoid hosts, the cod (Gadus morhua L.), means that this species has long been recognised in the scientific literature, and here the extensive literature concerning this potentially important and damaging pathogen is re-examined to provide an up to date overview, which includes both aquaculture and wild fisheries perspectives. Due to disagreements between several descriptions of the L. branchialis juvenile stages, and because the majority of the descriptions are over 60 years old, the juvenile free-swimming stages are re-described, using current terminology and a combination of both light and confocal microscopy. The time of hatching and moults in these stages is also examined. Techniques for the automated creation of taxonomic drawings from confocal images using computer software are investigated and the possibilities and implications of this technique are discussed. The method of host location in L. branchialis is unknown but is likely to involve a variety of mechanisms, possibly including chemo-reception, mechano-reception and the use of physical phenomena in the water column, such as haloclines and thermoclines, to search for fish hosts. In this study the role of host-associated chemical cues in host location by adult female L. branchialis is investigated by analysing the parasites behavioural responses to a range of host-derived cues, in both a choice chamber and a 3D tracking arena. To analyse the data from the experiments, specialised computer software (“Paratrack”) was developed to digitise the paths of the parasites’ movements, and calculate a variety of behavioural parameters, allowing behaviour patterns to be identified and compared. The results show that L. branchialis responds to host-associated chemical cues in a similar way to many copepods in the presence of chemical cues. Of the different cues tested, gadoid conditioned water appears to be most attractive to the parasites, although the wide variation in behavioural responses may indicate that other mechanisms are also required for host location. The different behavioural responses of parasites to whiting (Merlangius merlangus L.) and cod (Gadus morhua) conditioned water, which are both definitive hosts, provide some evidence for sub-speciation in L. branchialis. The role of chemical cues in host location of L. branchialis, and the relative importance of chemical and physical cues in host location are discussed. As well as demonstrating several techniques, which show potential for further development, this work has improved our knowledge of the biology and life-cycle of L. branchialis. Further study of this, and other areas of L. branchialis biology and its host-parasite interactions, should assist the development of contingency plans for the effective management and control of this widespread and potentially devastating pathogen.

Spatial patterns in parasite communities of freshwater fish are often characterized as low in diversity and unpredictable. Whether or not his view is a true reflection of community patterns is unclear, in particular when comparing studies of parasite communities of fish occuring in man-altered ecosystems. To understand the structure of a fish parasite community, I first described the parasite fauna of 13 species of freshwater fish from 19 isolated lakes on the Caribou Mountains plateau in northern Alberta. After my initial broad-scale survey, I selected the diverse and complex community of parasites in whitefish, (Coregonus clupeaformis) for further analysis. This host had the most diverse parasite community of any species of fish on the plateau and was disproportionally important in the dissemination of parasites to the other species of fish. Ten parasite species infected whitefish in the 7 large lakes on the plateau; 7 were core species (i.e found in every lake) and 9 were salmonid specialists. Parasite intensities were much higher (>100 per host) in the Caribou Mountains than elsewhere in Canada, as was community similarity (>70%). Ordination analyses showed that 48% of the variation in parasite intensities between lakes could be explained by factors associated with aquatic productivity (e.g. chlorophyll-a and total phosphorus). Low-intensity lakes were characterized by low productivity and high colour and high-intensity lakes were characterized by low productivity and high colour and high-intensity lakes had high prductivity and low colour. Patterns of high similarity between lakes, together with the association between aquatic productivity and community structure shows that the spatial structure of parasite communities can be predicted on the basis of a common suite of specialist, core species. / vii, 147 leaves : ill. ; 28 cm.

Ergasilus sieboldi has been reported from a number of trout fisheries in England and Wales. The population dynamics of this parasitic copepod in Rutland Water, a large reservoir in Central England was studied from 2003 to 2005. A combination of angler and net caught fish were examined to record numbers of adult females and egg production throughout each year. The parasite overwintered in large numbers on trout and commenced egg production in April which then continued until October/November. The prevalence of infection and the abundance of the parasite were very high in overwintered rainbow trout but these parameters then decreased in March as large numbers of uninfected fish were stocked into the reservoir. The parasite population then increased until October. Infection levels in 2004 and 2005 were significantly lower than in 2003. Infections of cage-held rainbow trout showed that E.sieboldi could become ovigerous within two weeks of attachment to trout in July and August. New infections occurred from June until November. Several species of coarse fish examined were also shown to be infected by the parasite. Cage trials showed that triploid rainbow trout were infected by significantly higher numbers of the parasite than diploid rainbow, brown trout or “blue” rainbow trout. Observations of infected fish in experimental tanks showed that overwintering parasites were stimulated to commence oviposition by increasing water temperatures. Photoperiod had no noticeable effect on the parasite. Egg viability and rate of development was studied using tank held infected fish and in vitro incubation techniques. Viability of eggs in sacs detached from the adult parasite was greater than those remaining attached. The rate of egg development was modelled and was shown to be predicted by temperature. Development of eggs was estimated to commence at 3.6ºC. Eggs developed more rapidly at higher temperatures and at peak production, inter-clutch interval was between 0 and 0.5 days. Egg production models estimated that an overwintered parasite could produce up to 19 clutches of eggs between April and October under normal temperature regimes measured at the reservoir. Ovarian development during the winter was confirmed using classifications of ovary size and shape based on parameters measured using image analysis techniques. The life span of E.sieboldi was estimated at 10-12 months. Nauplii culturing techniques were compared, and nauplii to stage V were successfully developed. Nauplii hatched from the eggs of adult parasites occurring in the spring were larger and conditioned to develop at lower temperatures than those hatched later in the year. Nauplii were fed on 4 different types of algae held in monocultures but development occurred only in algal polycultures. A comparison was made of nauplii feeding preferences and development with algae recorded in Rutland Water in 2003 and 2005 but no correlations were found. Fish stock assessment was carried out using models of angler catch, effort and stocking figures from the fishery. Parasite numbers on the overwintered fish were estimated at 12 million parasites in April 2003, 8.3 million in April 2004 and 1.2 million in April 2005. Stock assessments suggested a reduction in number of overwintering trout and effects of stocking policy to be at least partially responsible for the decline in the parasite population. The results of this study formed a management strategy for the operation of the trout fishery.

M.Sc. / The catchment area of the Olifants River has, over a number of years, been exposed to extensive mining, agriculture and urbanisation activities in the Witbank-Middelburg and Phalaborwa regions which has largely contributed to the deterioration of water quality. Of major concern is the influence anthropogenic activities have on the aquatic ecosystem of the Olifants River within the Kruger National Park and how me health of fish residing In these waters is affected. To determine fish health, a biological monitoring method, the Health Assessment Index (H41), was tested for the first time In South Africa. Four surveys were conducted at Mamba and Balule In the Olifants River, Kruger National Park during 1994 (February, May, July and November). An additional survey was conducted in February 1995 at Loskop Dam. Samples of water and sediment were taken for analysis of metals and physical and chemical water parameters. A maximum of 20 Clarias gariepinus fish were sampled at each location. Evaluation of the fish was done according to guidelines set in the HAI and parasite population composition (prevalence, abundance, mean intensity) was determined. Organ and tissue samples including gills, liver, muscle and skin were analysed for the bioaccumulation of chromium, copper, Iron, manganese, nickel, lead, strontium and zinc, using atomic absorption spectrophotomeby. Metal concentrations in the water at Mamba and Balule were within guideline limits, whereas concentrations at Loskop Dam were above guidelines. As reflected by the application of the Aquatic toxicity Index, Loskop Dam presented with the poorest water quality followed by Mamba then Balule. It was found that certain physical and chemical variables namely fluoride, potassium, sulphate and total dissolved solids concentrations at Mamba and Balule were relatively high, particularly during drier months. Metals accumulated in organs and tissues, with the highest concentrations In the gills followed by the liver, skin and muscle. The discriminant analysis, utilising metal bloaccumulation, discriminates between water quality at Mamba and Balule, revealing a 100 % classification probability for each survey. Values obtained In the application of the HAI indicated that variables with good predictor accuracy were plasma protein, all parasites, endoparasites, liver, white blood cell counts, ectoparasites, skin, fins and gills. The discriminant function for the HAI generally Indicated variables similar to those exhibiting high predictor accuracy. The discriminant function showed relatively low classification probability for each survey. In case 1, where separate endo- and ectoparasite variables were Included in the determination of me discriminant function, probability for me entire study ranged between 47.5 % and 84.2 %. In case 2, where endo- and ectoparasite variables were given a refined score rating system, probability ranged between 62.5 % and 100 %. The low classification probability Indicates either the Importance of repetitive testing for this technique or a total departure from it. Results showed that fish populations with higher HAI values are found in water of poorer quality (Mamba), while healthier fish populations i.e. with lower RAI values are found In water of better quality (Balule). Parasite data shows a similar tendency by indicating that ectoparasites are abundant in water of higher quality, while endoparasftes increase in water of poorer quality. The HAI reflects the condition of fish populations in relation to their aquatic environment, therefore, the HA/ gives an indication of water quality and should be used as a first level screening tool. If complemented by a parasite survey, distinguishing between endoand ectoparasites, the results from the HAI will be enhanced.

Streptococcus agalactiae is a pathogen of multiple hosts. The bacterium, an aetiological agent of septicaemia and meningo-encephalitis in freshwater and saltwater fish species, is considered a major threat to the aquaculture industry, particularly for tilapia. Cattle and humans are however the main known reservoirs for S. agalactiae. In humans, the bacterium (commonly referred to as Group B Streptococcus or GBS) is a member of the commensal microflora of the intestinal and genito-urinary tracts, but it is also a major cause of neonatal invasive disease and an emerging pathogen in adults. In cattle, S. agalactiae is a well-recognized causative agent of mastitis. Numerous studies focusing on S. agalactiae from human and bovine origins have provided insight into the population structure of the bacterium, as well as the genome content and pathogenic mechanisms through identification of virulence determinants. Concerning S. agalactiae from aquatic origins, scientific information mainly focused on case reporting and/or experimental challenges, with a limited or absence of information in terms of pathogenesis, virulence determinants and genotypes of the strains involved. The objective of this study was to enhance our understanding of the molecular epidemiology, host-adaptation and pathogenicity of S. agalactiae in aquatic species, with particular emphasis on tilapia. Firstly, a collection of 33 piscine, amphibian and sea mammal isolates originating from several countries and continents was assembled, with the aim of exploring the population structure and potential host specificity of aquatic S. agalactiae. Isolates were characterised using pulsed-field gel electrophoresis (PFGE), multi-locus sequence typing (MLST), and a standardised 3-set genotyping system comprising molecular serotypes, surface protein gene profiles and mobile genetic element profiles. Two major subpopulations were identified in fish. The first subpopulation consisted of non-haemolytic isolates that belonged to sequence type (ST) 260 or 261, which are STs that have been reported only from teleosts. These isolates exhibited a low level of genetic diversity by PFGE and clustered with other STs that have been reported only in fish. Another common feature was the absence of all surface protein genes or mobile genetic elements targeted as part of the 3-set genotyping and that are usually found in human or bovine isolates. The second subpopulation consisted of β-haemolytic isolates recovered from fish, frogs and sea mammals, and that exhibited medium to high genetic diversity by PFGE. STs identified among these isolates have previously been identified from strains associated with asymptomatic carriage and invasive disease in humans. The human pathogenic strain ST7 serotype Ia was detected in fish from Asia. Moreover, ST283 serotype III-4 and its novel single locus variant ST491 detected in fish from Southeast Asia shared a 3-set genotype identical to that of an emerging ST283 clone associated with invasive disease of adult humans in Asia. These observations suggested that some strains of aquatic S. agalactiae may present a zoonotic or anthroponotic hazard. STs found among the seal isolates (ST23) have also been reported from humans and numerous other host species, but never from teleosts. This work provided an excellent basis for exploration of the virulence of selected strains in experimental challenges. The virulence of two strains of S. agalactiae was experimentally investigated by intra-peritoneal infection of Nile tilapia (Oreochromis niloticus), using an isolate originally recovered from fish and belonging to ST260, and an isolate originating from a grey seal and belonging to ST23. The clinical signs, the in vivo distribution of viable bacteria and bacterial antigens, and the gross and histopathological lesions that developed during the time course of the infection were investigated. The ST260 strain was highly virulent, whereas no major clinical sign or mortalities occurred in the fish challenged with the ST23 strain. After injection, both strains however gained access to the bloodstream and viable bacteria were recovered from all organs under investigation. During the early stages of infection, bacteria were mostly found within the reticulo-endothelial system of the spleen and kidney. Thereafter, the ST260 demonstrated a particular tropism for the brain and the heart, but granulomatous inflammation and associated necrotic lesions were observed in all organs. ST23 was responsible for a mixed inflammatory response associated with the presence of bacteria in the choroid rete and in the pancreatic tissue only. After 7 days post-challenge and for both strain, the formation or containment of bacteria within granulomata or other encapsulated structures appeared to be a major component of the fish response. However, the load of viable bacteria remained high within organs of fish infected with ST260, suggesting that, unlike ST23, this strain is able to survive within macrophages and/or to evade the immune system of the fish. This work demonstrates that the lack of report of ST23 strains in fish is possibly not due to a lack of exposure but to a lack of virulence in this host. The two strains, which differ in prevalence and virulence in fish, provide an excellent basis to investigate genomic differences underlying the host-association of distinct S. agalactiae subpopulations. The genome of the ST260 strain used in challenge studies was sequenced. We therefore provided the first description for the genome sequence of a non-haemolytic S. agalactiae isolated from tilapia (strain STIR-CD-17) and that belongs by multi-locus sequence typing (MLST) to clonal complex (CC) 552, which corresponds to a presumptive fish-adapted subgroup of S. agalactiae. The genome was compared to 13 S. agalactiae genomes of human (n=7), bovine (n=2), fish (n=3) and unknown (n=1) origins. Phylogenetic analysis based on the core genome identified isolates of CC552 as the most diverged of all S. agalactiae studied. Conversely, genomes from β-haemolytic isolates of CC7 recovered from fish were found to cluster with human isolates of CC7, further supporting the possibility that some strains may represent a zoonotic or anthroponotic hazard. Comparative analysis of the accessory genome enabled the identification of a cluster of genes uniquely shared between CC7 and CC552, which encode proteins that may provide enhanced fitness in specific niches. Other genes identified were specific to STIR-CD-17 or to CC552 based on genomic comparisons; however the extension of this analysis through the PCR screening of a larger population of S. agalactiae suggested that some of these genes may occasionally be present in isolates belonging to CC7. Some of these genes, occurring in clusters, exhibited typical signatures of mobile genetic elements, suggesting their acquisition through horizontal gene transfer. It is not possible to date to determine whether these genes were acquired through intraspecies transfer or through interspecies transfer from the aquatic environment. Finally, general features of STIR-CD-17 highlighted a distinctive genome characterised by an absence of well conserved insertion sequences, an abundance of pseudogenes, a smaller genomic size than normally observed among human or bovine S. agalactiae, and an apparent loss of metabolic functions considered conserved within the bacterial species, indicating that the fish-adapted subgroup of isolates (CC552) has undergone niche restriction. Finally, genes encoding recognised virulence factors in human S. agalactiae were selected and their presence and structural conservation was evaluated within the genome of STIR-CD-17.

M.Sc. (Zoology) / The world’s ever increasing human population has lead to an almost unimaginable amount of waste being released in to the aquatic environment every day. Aquatic systems are faced with the greatest risk due to the fact that water is an indispensable resource required for industrial and agricultural processes. In recent years there has been a dire need for the monitoring and rehabilitation of aquatic systems. As a result many biological monitoring programmes were set into place in an attempt to manage this problem. The use of aquatic organisms as sentinels for biomonitoring studies has been wildly accepted with the majority of biomonitoring research focusing on the use of various fish and invertebrate species as aquatic sentinel organisms. However, the use of parasites as sentinel organisms is a relatively new field and as a result there has been little published work on the use of monogenean ectoparasites parasites as such sentinels. The bioaccumulation and subsequent biomagnification of metals by certain parasite species is well known, with bulk of the published work focusing on endoparasites (cestodes, acanthocephalans & nematodes), these published studies indicate that some species of endoparasites exhibit a remarkable ability to biomagnify metals in concentrations that far exceed that of their respective hosts as well as the ambient environment. Thus this project aims to assess the bioaccumulation and biomagnification of metals by the ectoparasitic diplozoon. The study site that was chosen for this project was the Vaal Dam; this site was deemed appropriate due to its near pristine condition and major economic importance. This meant that this particular site is ideal for the testing of a new biomonitoring system. All field sampling was performed around UJ Island (26°52.249’S; 20°10.249’E) from February 2011 to April 2011. A total of 29 Labeo umbratus (Smith, 1841) were collected with the aid of gill nets and three sediment samples were also taken using a grab sampler. Water quality data was obtained from the Rand Water Analytical Facility in Vereeniging as this organisation routinely monitors of the water quality parameters and the metal concentrations within the surface waters of the Vaal Dam, this information was obtained with the aid of data loggers situated in the dam...