M.Sc. / The tigerfish, Hydrocynus vittatus, is one of the most sought-after game fish in Southern Africa, and a vital source of protein and income in contiguous communities. Unfortunately, this species has been placed on the protected species list, alongside the infamous great white shark (Carcharodon carcharias). The loss of this species will not only be disadvantageous to local communities, but will also have a damaging impact on the Southern African tourism industry. After reviewing all available literature on tigerfish, it was noted that studies on the genetics, morphology, distribution, age, growth and maturity were severely lacking. Research on the Pongolapoort Dam and Phongolo River tigerfish was also practically nonexistent. The aims of this study were therefore to: (1) analyse the genetic variation and diversity of five Southern African tigerfish populations and comment on the use of the various populations as possible candidates for restocking; (2) assess whether the genetic composition and caudal colour can be linked to the biogeography of the species; (3) determine the growth patterns of tigerfish otoliths and establish the best ageing technique for this species; and (4) determine the age structure of tigerfish from the Pongolapoort Dam in KwaZulu-Natal, South Africa. Before analysing the genetic composition of various tigerfish populations, it was hypothesised that individuals from the Okavango and Phongolo systems would possess the highest and lowest heterozygosity, respectively. Tigerfish from the Olifants River would be the best choice of brood stock, should population restocking become necessary. The muscle and liver tissues of 117 tigerfish from the Upper Zambezi, Okavango Delta, Olifants and Phongolo Rivers and Pongolapoort Dam, were assessed by starch gel electrophoresis.

Ph.D. / Since the systematics in the family Characidae from southern Africa were only reliant on some morphological traits, the determination of the genetic variation, genetic distances and phylogenetic relationships using different molecular techniques led to the formulation of this study. The first aim of the study was to describe the amount and pattern of genetic variation withi~ and between populations. The analysis of the isozymes provided the first account of the amount. pattern and distribution of genetic variation within this family. A general introduction on the history, distribution, descriptions, taxonomy and some ecological notes from the literature on southern African Characidae species is included in Chapter l. The second chapter dealt with the Hydrocynus genus that represents, morphologically, the largest member of this family. Other members of the Characidae family are relatively small species that do not exceed 300g. Twenty-five enzyme coding loci in two populations of H. vittatus, from Namibia and South Africa, were analyzed by horizontal starch gelelectrophoresis. Electrophoretic analysis of liver. white muscle, heart and testis samples revealed genetic variation at 20% (Upper Zambezi River. Namibia) and 36% (Oiifants River. South Africa) of the protein coding loci studied. Average heterozygosity values ranged from l .9% (Upper Zambezi River) to 4.6% (Oiifants River), with a genetic distance value of 0.005 between these populations. The low amount of genetic variability in the former population compared to that of other fish species from the same geographical area, and to that of H. vittatus from the Olifants River. can be attributed to restricted gene flow due to isolation. Although morphological differences exist between the two populations. the extent thereof is not sufficient to regard them as subspecies.

Ph.D (Zoology) / The Characiformes, which are widespread in Africa and the Neotropical Region, comprise a broad series of species with strong oral teeth, of which numerous are top predators in their respective areas of distribution. This is the case with the six Hydrocynus species (Alestidae), which are endemic to African fresh waters (Skelton, 2001) and better known as tigerfish, owing to their striped colour pattern and prominent oral teeth (Jubb, 1967). As top predators they play a significant role in the functioning of riverine eco-systems, in particular as regards the transfer of energy from the floodplains to the main rivers (Winemiller & Kelso-Winemiller, 1994). Also as top predators they contribute to the maintenance of diversity in these eco-systems and to stabilize the energy acquired by their prey during their growth in the eutrophic floodplain. They also contribute substantially to inland fisheries, notably to the recreational side, since they are deservedly ranked among the most spectacular freshwater game species. Despite their ecological importance there is a dearth of knowledge on their ecology and behaviour, accept for a few dedicated studies (Baras et al., 2002). Tigerfish have a tropical distribution, but some species, such as Hydrocynus vittatus ranges to the southern limit of the inter-tropical region and is found in South African waters. In South Africa, H. vittatus occurs in the lowveld reaches of coastal systems north of the Phongolo River (Skelton, 2001). The species was formerly reported at altitudes greater than 300 m above sea level in Mpumalanga, Swaziland and Kwazulu Natal (Gaigher, 1969). Nowadays its distribution is restricted to the lower reaches of these rivers. In the Incomati River system, most historical records suggest that H. vittatus occurred up to the confluence of the Komati and Mlumati rivers, a distance of 50 km upstream from Komatipoort...

M.Sc. / The practice of catch-and-release (C&R) fishing has been widely promoted as a conservation strategy and fisheries management tool and is currently considered an ecologically sustainable practice. Factors negatively affecting fish as well as mortality have, however been shown to occur. The overall aims of this study were to determine the effect of C&R angling on tigerfish Hydrocynus vittatus and Vaal-Orange smallmouth yellowfish Labeobarbus aeneus by studying the physiological stress response as well as age, growth and reproductive characteristics. To determine the physiological response of tigerfish (n=63) and smallmouth yellowfish (n=96) data were collected during August/September 2008 (Okavango Delta) and from June 2008 through to December 2008 (Vaal River) for the respective species. Fish were collected using standard angling and fly-fishing techniques, anaesthetised in clove oil and blood drawn from the caudal veins; thereafter fish were weighed and measured, revived and released. To serve as controls, randomly selected fish (from each species) were kept for 72 h in pools filled with river water. Blood plasma was analysed for concentrations of glucose, cortisol and lactate to determine the effects of angling duration, fish size, and water temperature. In both species larger fish were shown to be angled for a longer duration compared to smaller fish. Levels of glucose, at times, were affected by water temperature (influenced by time of year). Plasma glucose concentrations in H. vittatus showed a slight increase whereas levels in L. aeneus decreased with greater angling durations. Few individuals from each species, (n=13 for H. vittatus and n=12 L. aeneus) showed significantly increased plasma cortisol concentrations. Lactate concentrations were found to increase significantly above control values in H. vittatus angled for < 1 min and L. aeneus angled for > 1 min. Increased handling durations of captured H. vittatus that had been angled for < 1 min showed a significant increase in plasma lactate concentrations. Results from the control fish indicated that baseline levels of lactate in H. vittatus and cortisol and lactate in L. aeneus were restored within 72 h of capture. The relative age of the selected species were determined with the aid of scales, lapillus otoliths (H. vittatus) and asteriscus otoliths (L. aeneus) The most appropriate methods found for ageing the two species were sectioned lapillus otoliths for H vittatus and whole asteriscus otoliths for L. aeneus. Males and females from both species were found throughout the age classes. Male and female H. vittatus had a longevity of 20 years and 16 years respectively, similarly, male and female L. aeneus had longevities of 19 years and 15 years respectively (relative age for both species). Summary 11 Hydrocynus vittatus males matured at a total length (TL) of 451mm and females matured at 522mm TL, corresponding to an approximate relative age of 4 years for both sexes. Labeobarbus aeneus males matured at a fork length (FL) of 289mm and females matured at 367mm FL, corresponding to relative ages of 4 and 6 years respectively. This is the first study of its type reporting on the physiological response of African freshwater game fish species as well as the first report of age determination of H vittatus in the Okavango Delta and the first for this species using otoliths. While the age of various L. aeneus populations have been studied this is the first time that otoliths are used in the Vaal River population. This study confirms that the physiological response, and potential negative effects of C&R are species specific, and that studies should be done on all targeted freshwater game fish species to ascertain the physiological stress imposed by C&R angling.

M.Sc. (Zoology) / This investigation is divided into two sections. Section A deals with aspects of the spermatology of the tiger fish and section B deals with the cryopreservation of spermatozoa of selected freshwater fish species.

M.Sc. / Hydrocynus vittatus, commonly known as the tigerfish, plays an important role in riverine ecology. It is a top predator which roams the open waters of most larger river systems in southern Africa. Their presence in a freshwater ecosystem has a dramatic impact on the fish community structure. It is known that dams and weirs have a negative effect on the migration of the tigerfish. It is also evident that tigerfish do not occur in certain areas in some of the rivers where they have been present historically. The Olifants and Letaba Rivers in the Kruger National Park (KNP) are two of a few rivers within South Africa where tigerfish do occur. The KNP represents the edge of the most southern distribution of tigerfish in southern Africa. It was therefore expected that the tigerfish do not function optimal in the Olifants and Letaba Rivers as they are subjected to waters with high concentrations of silt and low flow which influences migration and successful breeding. Breeding migrations does however take place during the summer months after which the tigerfish returns to the Massingire Dam in Mozambique to avoid the colder winter temperatures in the rivers. Gonad development coincide with the yearly summer rainfall patterns. A deviation of the expected 1:1 male:female sex ratio to favour the males was experienced in both rivers, which may be the result of over population. Females were found to grow to a larger size than the males and were extremely fecund. Although H. vittatus is believed to be mainly piscivorous, other food items such as invertebrates, played an important role in the diet of small and large tigerfish in both the Olifants and Letaba Rivers. Invertebrates were mostly preyed upon which implies that optimal feeding conditions for the tigerfish does not prevail in these systems and that they have to adapt to satisfy their feeding requirements. Tigerfish is more abundant in the Olifants than in the Letaba River. The overall growth performance or phi prime (4)) values for H. vittatus in the Olifants River was determined and compares well to the overall growth performance of tigerfish in the Okavango River and Lake Kariba. However the maximum length calculated for tigerfish in the Olifants River (Lco = 52.40 cm ) is smaller than the Lco values (56.06 cm) for the Okavango River. The mortality rate of tigerfish in the Olifants River exceeds those in the Letaba River which means that the life expectancy is longer in the Letaba as opposed to the Olifants River. Successful artificial spawning revealed some of the secrets of the reproduction strategy of this species. Tigerfish has semi pelagic eggs, are very small (0.65 mm), negatively buoyant and slightly adhesive for bentic and epibiotic incubation, and it is expected that tigerfish would spawn in open water, on a sandy substrate in the vicinity of aquatic vegetation. First hatching took place at 22h 30 min after fertilization. Vertical movement of the larvae lasts for two days, which allows for downstream movement and dispersement of the larvae. It was found that tigerfish replace their teeth on a regular basis as they grow larger. Transition from conical to functional dentition takes place 45 days after hatching. Replacement of sets of teeth occurs during all phases of its lifespan. It is a quick proses of three to six days during which all teeth are replaced in both the upper and lower jaws.

M.Sc. (Environmental Management) / The Kruger National Park (KNP) is a world renowned wildlife reserve and a source of South African ecotourism benefiting the economy. The Olifants River is the largest river running through the KNP and it is known to be one of South Africa’s most polluted rivers. In the winters of 2008 and 2009 Nile crocodile carcasses were found in the Olifants River gorge in the KNP. In a very short period nearly the entire population of Nile crocodile was lost, the cause of which was later identified as pansteatitis. Pansteatitis is caused by lipid peroxidation known to be nutritionally mediated, as it is associated with diets high in polyunsaturated fats, often of fish origin and insufficient antioxidants specifically vitamin E, which is solely synthesized by plants and must therefore be obtained through diet. The hypothesis of this study is therefore that the fish inhabiting the Olifants River are antioxidant deficient, more specifically, vitamin E deficient, causing the wildlife e.g. crocodiles and predatory fish species, that feed on the fish, to become vitamin E deficient as well, and subsequently develop pansteatitis. If the hypothesis is true, the top fish predator in this aquatic system, the tigerfish Hydrocynus vittatus, should therefore also exhibit signs of dietary vitamin E deficiency. The aim of this study was to determine if tigerfish from the Olifants River in the KNP are exhibiting any signs of antioxidant deficiency, specifically vitamin E deficiency. The objectives to accomplish this aim were firstly to analyse the total plasma antioxidant activity using an ELISA assay, and secondly, to perform a histology-based fish health assessment on the target organs of the tigerfish to identify any histological alterations, specifically those known to be associated with vitamin E deficiency. The results were compared to the results from fish of the same species from two reference sites where there have been no signs of vitamin E deficiency, such as pansteatitis-related wildlife deaths. The results of the plasma analysis as well as the histological assessment showed no conclusive signs of vitamin E deficiency in tigerfish from the Olifants River. It is therefore unlikely that the pansteatitis in the affected wildlife is caused by dietary vitamin E deficiency in the aquatic system, but rather by vitamin E depleting mechanisms such as the presence of high amounts of toxicants with pro-oxidant properties, which may be causing an imbalance of pro-oxidants and antioxidants within the body. Hence the rate of vitamin E regeneration cannot keep up with the rate of oxidation. This is occurring only in certain species due to their specific behaviour or eating habits.

M.Sc. / The tigerfish, Hydrocynus vittatus member of the Alestidae, are ferocious and fierce predators capable of consuming prey up to 40% of their size. In South Africa H. vittatus can be found in the major east-flowing rivers from the Limpopo River to the Phongolo River flowing into the Pongolapoort Dam making up the southernmost population. The Pongolapoort Dam also known as Lake Jozini is located in the high-rainfall subtropical region of northern KwaZulu-Natal. The Pongolapoort Dam wall was completed in 1973 to make it the fifth largest dam in South Africa with a total surface area of 2 445.9 x 106 m2. It was primarily built for the irrigation of sugar-cane in the surrounding regions. The Fish Health Assessment Index is used as a quantitative index that identifies morphological alterations and assigns them a score for statistical comparison. The main purpose of the macroscopic Fish Health Assessment Index is to detect gross changes in the health of fish populations through necropsy early enough for remedial actions to be put into place. Histopathology is used as an important diagnostic tool for detecting infectious and non-infectious diseases and can therefore be used to assess the health of fish populations by analysing selected target organs. Catch and release (C&R) angling has become a very widely promoted conservation tool as sport angling continues to increase. Anglers release their fish under the assumption that the fish will survive; however, the end results have been shown to vary greatly, from death of the fish to sub-lethal end points such as exhaustive exercise, injury and/or air exposure which will affect the fitness of the fish. The first aim of the study was to determine the health status of H. vittatus and C. gariepinus from the Pongolapoort Dam by means of a histology-based fish health assessment protocol applied to a total of 45 H. vittatus specimens collected in February 2009 (n = 30) and July 2009 (n = 15) and a total of 19 C. gariepinus specimens collected in October 2009 (n = 10) and April 2010 (n = 9). In the H. vittatus specimens DDT was found in the axial muscle; the concentrations of these in February 2009 (5 403.9 ng∙g-1 lipid) and July 2009 (5 537.4 ng∙g-1 lipid). The Mean Index values showed that the Kidney Index (IK), Gill Index (IG) and Fish Index (IFISH) were higher in fish from the February survey while the Liver Index (IL) was higher in those collected during July. Liver alterations identified included intercellular oedema, granular degeneration, vacuolation, nuclear pleomorphism and lymphocyte infiltration. Kidney alterations included dilation of the glomerulus capillaries, vacuolation and hyaline droplet degeneration. Gill alterations identified included telangiectasia and hyperplasia of the secondary lamella, congestion, and rupture of pillar cells.

M.Sc. (Zoology) / The construction of the Pongolapoort Dam in 1974 has altered conditions downstream of the Phongolo River in terms of hydrology, geomorphology, water quality, and ecosystem services. Activities along the Phongolo River permit anthropogenic compounds such as pesticides used in disease control to enter the aquatic environment. This alteration of natural environmental conditions creates a need for a monitoring programme. This study aims to assess the use of Hydrocynus vittatus as an indicator organism of pollution in the Nyamithi Pan and Phongolo River. Water and sediment samples were analysed for a variety of metal elements. The physical characteristics of water samples were determined using a WTW Multi 340i multimeter. Nutrients in water were analysed using a Merck Spectroquant™ Pharo 100 Spectrophotometer. Sediment analysis was based on the standard protocols of the United States Environmental Protection Agency (2001). Physiological stress responses in Hydrocynus vittatus were determined using acetylcholine esterase, catalase, cellular energy allocation, 7-ethoxyresorufin-O-deethylase, malondialdehyde, metallothionein, superoxide dismutase, and protein carbonyls. Employing standard techniques H. vittatus was analysed for metals and organics using ICP-MS, ICP-GS and ICP-OES. Results for biological responses and bioaccumulation show significant differences between sites related to the environmental concentrations of elements. Organisms in the Phongolo River have elevated concentrations of DDT and the metabolites indicating recent exposure. Organisms from the Phongolo River are seen to be responding based on up or down regulated concentrations of biological markers. In particular, concentrations of CAT, MDA and PC are elevated in the Phongolo population with decreased AChE responses indicating toxicant exposure. Data accumulated in this study will contribute to the establishment of baseline chemical, physical and biological knowledge of the effects of contamination in South African waters.

M.Sc. / Pollutants present in minute concentrations in aquatic environments and which possess long residence times may be accumulated by aquatic organism such as fish, resulting in adverse affects. Bioaccumulation and biomarker responses are often used to qualify and quantify pollutant exposure and effect, and for this reason form a major part of many environmental assessments. To interpret bioaccumulation and biomarker responses the physico-chemical parameters of the environment should be known. This study aimed to spatially and temporally assess the environmental partitioning of heavy metals in three South African freshwater systems, namely the Pongolapoort Dam, Olifants and Luvuvhu Rivers, and to relate these concentrations to bioaccumulation and biomarker responses in tigerfish, Hydrocynus vittatus. This is because there is relatively little known about the bioaccumulation potential and stress responses of tigerfish to pollutants and they have recently become listed as a protected species. Result from this study showed that there were few differences between seasons in terms of metal bioaccumulation in the Pongolapoort Dam with the exception of Se, Zn and Fe. Selenium and Fe concentrations were linked to concentrations found in the environment, whereas Zn was attributed to a disruption in homeostasis within the fish. Increases in MT were found during the winter months and were attributed to increased metal concentrations at this time, namely Zn and Se, whereas decreases in CEA and PC were observed at this time and were linked to depleted energy reserves, stress and a reduction in the presence of pesticides as a result of decreased runoff during the winter months. It was found in the Olifants and Luvuvhu Rivers that there were no distinct decreases in metal concentrations as the rivers flowed through the KNP, and processes such as rainfall, remobilization of sediments, distance of the study area from the source and geology played a great role in the distribution of metals. Metal concentrations in the Olifants River water, sediment and fish were, for the most part, found to be lower than previous studies, possibly due to improvement in management strategies or increased buffering of this river. Only Al and As were significantly higher in tigerfish from the Olifants River, and this was reflected in high MT concentrations. It was suggested that tigerfish from the Olifants River have developed effective mechanisms for the excretion and detoxification of heavy metals that they are exposed to as a result of extended exposure. Concentrations of AChE were also significantly inhibited in tigerfish from the Olifants River which is indicative of greater concentrations of organophosphates and carbamate pesticides than the other sites. Tigerfish from the Pongolapoort Dam had signifcantly higher levels of MT and significantly inhibited concentrations of AChE in comparison to tigerfish from the Luvuvhu River. The tigerfish from the Luvuvhu River had significantly higher concentrations of Se in muscle tissue. Tigerfish from the Luvuvhu River, also experienced stress as a result of pollution as was apparent from significantly depleted energy reserves in comparison to the other sites under study, and higher concentrations of PC and CYP1A which are typical biomarkers responding to halogenated and aromatic pesticides, such as deltamethrin and endosulfan. It was recommended that further studies be done to assess the presence of pesticides within these systems to determine the contribution of these pollutants to the state of tigerfish