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

M.Sc. (Zoology) / Milt and blood samples of Aarbus aeneus were collected during November in order to perform chemical analyses of the blood and seminal plasma. Physical analyses were also carried out on milt. Throughout the year testes were collected in order to determine the stages of testicular development. This was done by means of histological analyses. The sperm counts averaged 8,41 x 10-3 cells rom while the spermatocrit value varied between 44% and 82% (average of 61,9%). All the milt samples collected were white in colour showing a high viscosity. Sperm motility gradually declined after activation and stopped after 82,5 seconds. Chemical values of the components tested in the blood plasma were statistically compared to those in the seminal plasma and no statistically significant differences were recorded between sodium, potassium, chloride, calcium, magnesium, glucose, total lipid, total proteien concentrations, osmolality and pH. The only component where a difference in concentration occured was fructose (30% probability). Sodium, calcium, magnesium, glucose, fructose, total lipid and total proteien concentrations in the blood plasma were significantly lower than the corresponding concentrations in the seminal plasma. In contrast the potassium concentration were higher in the seminal plasma. The pH of the seminal plasma (8,63) was alkaline while a pH of 7,5 was recorded for blood plasma. In the two lobe testis of Barbus aeneus semen is collected with seminiferous ducts into the vas deferens which together with the blood vessels are housed within a hilus. The testis is surrounded by a tunica albugenea and the seminiferous lobules are filled with cysts. The testis of the smallmouth yellowfish appears to be lobular and sperm are deposited into lumens which exist between the cysts. During the resting phase the interstitial tissue is very difficult to distinguish and is seen as a thin layer of cells between the lobules seperating them from one another...

The smallscale yellowfish (Labeobarbus polylepis, Cyprinidae), is a large yellowfish species restricted to the southern tributaries of the Limpopo, Incomati and Pongola river systems. This temperate species does not occur below altitudes of 600m and is restricted to perennial rivers with riffles/runs and deep pools. As with most yellowfish species in southern Africa this species is rapidly declining from its known localities. Because of the numerous dams and weirs in rivers, their breeding migrations are often restricted, and the associated flow regimes probably impact on the environmental cues that are a pre-requisite for successful reproduction. Little or no information is available on the breeding ecology of this species. There was thus the need to quantify reproduction requirements of Labeobarbus polylepis assisting aquatic scientists in ensuring flow requirements, conserving spawning habitats and preventing anthropogenic impacts that influence reproduction behaviour and environmental cues. During this study an in-depth investigation was done on the reproductive strategy of Labeobarbus polylepis. This included the habitat requirements, environmental cues associated with spawning, spawning behaviour and the artificial propagation of this species, as well as describing the early life history stages. From results obtained it is evident that this species spread its reproductive effort over a short period in the early summer season (October). A definite spawning behaviour pattern was observed during this study, which only occurred when environmental cues (daylight length, water temperature and constant low flow) coincides with optimal habitat requirements for spawning. Three definite stages were identified namely pre-spawning behaviour, spawning behaviour and post-spawning behaviour, that is described accordingly. From the observations made during natural spawning, as well as induced spawning, it appears that this previously thought multiple/ serial spawner is in fact a single event spawner. Also, the observed similarity between stream velocity, depth, substrate composition and layout of spawning beds suggest that this species is highly selective in terms of its habitat requirements for breeding. In the developing embryo, the relatively large periviteline space confirm that the eggs are also adapted to fast flowing waters in order to prevent the harmful effects of flow turbulence. Results of this study conclude that Labeobarbus polylepis is a highly specialised breeder that is sensitive to river regulation. / Prof. G.J. Steyn Prof. F.H. van der Bank

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) / Please refer to full text to view abstract

M.Sc. Zoology / Only a few species of the family Diplozoidae have previously been described from Africa, from various Labeo and Barbus species. An investigation was undertaken respectively in the Vaal Dam and Vaal River Barrage in the Vaal River system, South Africa to determine aspects of the morphology, taxonomy and ecology of specimens of this family collected from the gills of Barbus aeneus. Various fish species, namely B. aeneus, Barbus kimberleyensis, Labeo capensis, Labeo umbratus, Cyprinus carpio, Clarias gariepinus and Micropterus salmoides, were collected with the aid of gill nets. The fish were killed and the length, weight and sex determined. The gills were removed from the left and right gill chambers, placed in separate, marked petri dishes and covered with water from the dam. Gills (from first to fourth pair) were examined with the aid of a dissection microscope. The position of attachment and the region on the gill namely dorsal, median or ventral, was noted. Parasites were removed, fixed between a cover slip and glass slide in steaming hot aceto-formaldehyde alcohol and preserved in 70 % ethanol. A morphological study was undertaken. Results of a Scanning Electron Microscopy study illustrated the following external characteristics namely a round opisthohaptor with four pairs of clamps, while study of whole mounts revealed larval hooks, a round-ended intestine and eggs without filaments. Graphic reconstruction of serial sections of the reproductive system of parasites embedded in resin revealed that the vas deferens of one individual opens into the common vitelline duct of the other. Parasites were identified as belonging to the genus Paradiplozoon. The morphological characteristics, namely the round opisthohaptor, intestine with rounded ending, egg without filament and morphological measurements, of various structures (for example, total body length) that differ from other species of this genus, led to the establishment of a new species, that is, P. alwinii.

A large sportfishery that targets both smallmouth (Labeobarbus aeneus) and largemouth (Labeobarbus kimberleyensis) yellowfish exists in South Africa. Both species have high conservation priority, and no assessments documenting the effect of angling on L. aeneus and L. kimberleyensis have been undertaken. The overall aim of this study was to provide an assessment of the impact of angling on L. aeneus and L. kimberleyensis. The specific objectives of this study were to characterise the sectors utilising Lake Gariep, document catch, effort and total catch for the fishery as well as the locality specific biology of L. aeneus and L. kimberleyensis. The study was undertaken on Lake Gariep, South Africa's largest impoundment, situated on the Orange River system in central South Africa. Subsistence fishers were the dominant user group, constituting 60 % of the fishery, the remainder constituted recreational anglers. Angler catches were dominated by carp (Cyprinus carpio; 74 %), followed by mudfish (Labeo capensis; 13 %) and smallmouth yellowfish (8 %). Catches of largemouth yellowfish contributed < 0.5 % to the total catch. The relative abundance of species by weight differed by area (χ² test of independence: χ² = 182, df = 4, p ≤ 0.05). On any sampling day time fished was the best predictor for differences in probability of capture (PC) (Wald X²(1) = 7.169, p = 0.007). The probability of capturing L. aeneus differed significantly between month (Wald X²(5) = 20.690, p = 0.000) and region (Wald X²(3) = 46.755, p = 0.000). The single best predictor of differences in log abundance and non-zero CPUE was region (Factorial ANOVA p ≤ 0.05). Mean CPUE ranged from 0.21 ± 0.06 kg. man⁻¹.hr⁻¹ to 0.82 ± 0.11 kg. man⁻¹.hr⁻¹ in the OV region and 0.42 ± 0.10 kg. man⁻¹.hr⁻¹ to 1.17 ± 0.24 kg. man⁻¹.hr⁻¹ in the GD region. Angler effort was higher in OV than in GD and ranged from 17 ± 3 anglers/day to 45 ± 9 anglers/day and 6 ± 1 anglers/day to 41 ± 8 anglers/day, respectively. Total catch was higher in the GD 46.0 [95 % CI = 15:102.6] t. period⁻¹ than the OV region 40.0 [95 % CI = 13.9:89.6] t. period⁻¹. The total catch from the Lake Gariep fishery between March and December 2007 was estimated to be 86.0 [95 % CI = 40.4:154.8] t. period⁻¹. Age and growth was determined using whole otoliths. The growth of L. aeneus was best described by the von Bertalanffy growth model as Lt = 481.80 (1- e⁻°·²²⁽t⁺°·⁶¹⁾). Gonadal development for L. aeneus was seasonal, with the gonadosomatic index peaking in January, revealing a distinct spawning season. The length at 50 % maturity for female L. aeneus was attained at a fork length of 354.7 mm. Natural mortality (M) was estimated at 0.55 year⁻¹. The growth of L. kimberleyensis was described by the von Bertalanffy growth model as Lt = 763.22 (1- e⁻°·¹¹⁽t⁺°·⁶³⁾). Only 6 mature female and 15 mature male L. kimberleyensis were recorded during the study period. The smallest mature female was a 390 mm FL stage four female and the earliest recorded mature male was a 337 mm FL, ripe running male. Natural mortality (M) was estimated at 0.08 year⁻¹ for L. kimberleyensis. Per recruit analysis indicated that current fishing mortality reduces the L. aeneus spawner biomass by 7 %, which is considered negligible. Labeobarbus kimberleyensis forms an insignificant proportion of anglers catches and stock status is currently considered pristine.

Colonisation theory relative to introduced populations was examined with a view to determining the usefulness of theoretical concepts in the prediction of the success of an invasion by a species. To this end, the Great Fish River, with reference to species introduced by the Orange/Fish Tunnel, was used as a case history. It was concluded that theoretical descriptions of population growth, control and decline are useful only when considering individual ecosystems or species. The highly variable nature of species and environments nullifies attempts to simplify behavioural characteristics into a predictive framework. There is an abundance of terminology associated with introduced organisms and frequently many of these terms are used synonymously. Eleven terms have been defined in this thesis with a view to standardising terminology. Characteristics of species and environments which enhance their susceptibility to invasions by exotic ichthyofauna were discussed and summarised. Distribution data concerning exotic fish introduced into the Great Fish River by the Orange/Fish Tunnel has demonstrated that, with the exception of Clarias gariepinus, all remaining exotics have restricted distributions. Only Barbus aeneus appears to be extending its range down the drainage. Age, Growth, reproduction and condition data support the conclusion that, excluding B. aeneus and C. gariepinus, invasive species in the drainage are not performing well. Of the five invasive species (B. aeneus, Labeo capensis, L. umbratus, Gephyroglanis sclateri and Cyprinus carpio), only two have established populations (B. aeneus· and C. gariepinus). Labeo umbratus and C. carpio were present on the Great Fish River prior to the construction of the tunnel and populations of the species could not be distinguished. It was concluded that there is no evidence to suggest that exotic species introduced into the Great Fish River are having a deleterious effect on indigenous, endangered ichthyofauna. Monitoring of the drainage should be continued to ensure that a danger to indigenous species does not develop.

D.Sc. (Zoology) / The spermatogenesis of two freshwater species from South Africa, Barbus marequensis and B. polylepis, and three fresh water species from Israel, B. canis, B. longiceps and Capoeta damascina, was studied. A histological comparison of the process of spermatogenesis was undertaken. The breeding cycle of B. marequensis, B. polylepis, B. canis, B. longiceps and C. damascina was similar to the breeding cycle of B. aeneus and four phases occured within the cycle. The four distinctive phases are post spawning phase, rest phase, pre-spawning phase and the spawning phase (Vlok, 1986) . During the post spawning phase a decline in sperm development is observed and possible lisosomal activity is responsible for the resorption of sperm cells not shed during the spawning phase. The presence of collagen structure provides a distinctive character to the tissue of the testis. The resting phase is characterised by the absence of the lobular structure and the testis is dominated by the collagen tissue. The testis is small and unobtrusive in the abdominal cavities of both species. At the onset of the pre-spawning phase, the testis is filled with spermatogonia. The lobular structure becomes more prominent and the interstitial tissue can be distinguished. Later during the phase, the synchronised development of sperm cells in the cysts of the lobules can be observed, whilst sperm cells in adjacent lobules are in different stages of development. During the spawning phase the testis of all species studied contain mature sperm . cells in the lumens of the lobules.

The construction of the Katse dam was completed in 1996. The dam started filling in 1995 and reached full capacity in early 1998. It forms part of Phase 1A of the Lesotho Highlands Water Project (LHWP). The main aim of the project is to provide revenue to Lesotho, by transferring water from the catchment of the Senqu (Orange) River in Lesotho to South Africa’s major industrial and population centres. During the implementation of the project, an estimated 130 people were displaced. However, the most serious impact has been the loss of the traditional way of life in the form of arable and grazing land as a consequence of inundation. One of the obligations of the project is to ensure that the standard of living of those affected by the project is not impaired. The Lesotho Highlands Development Authority identified a number of rural development projects, which included fisheries development. This study is an integral part of fisheries development in Lesotho. The aim of this study was to gain an understanding of the biology and the demographics of the fish species in the lake. This information would serve as the basis for the development of a management plan for the sustainable utilisation of the fisheries resources. To achieve this aim, the following specific objectives were addressed: 1. Investigation of the biology of the three principal species. 2. Description of the key population parameters (growth, mortality & recruitment). 3. Investigation of the distribution and relative abundance of the three species. The three principal species in the Katse dam are rainbow trout, Oncorhynchus mykiss, and the two cyprinids, Barbus aeneus and Labeo capensis. Sectioned otoliths were used to age O. mykiss while both otoliths and scales were used to age B. aeneus and L. capensis. Marginal zone analysis revealed that slow growth was experienced in winter for the three species. The maximum-recorded age for both B. aeneus and L. capensis was 12 years while O. mykiss reached 4 years. There was no significant difference in growth rates of the different sexes and growth was best described by the 3 parameter Von-Bertalanfy growth model as Lt = 603[1-e⁻°·¹⁵⁽t ⁺ °·°³⁾] for B. aeneus, Lt = 526[1-e⁻°·²¹⁽t ⁺ °·⁹⁾] for O. mykiss and Lt = 521[1-e⁻°·¹⁷⁽t ⁺ °·²¹⁾] for L.capensis. Male and female O. mykiss attained 50% sexual maturity (Lm₅₀) at 235 and 275mm FL, respectively. There was no difference in Lm₅₀ for male and female B. aeneus and L. capensis. B. aeneus reached sexual maturity at 285mm FL while L. capensis reached sexual maturity at 244mm. Both cyprinid species spawned in summer (November to January) while O. mykiss spawned in winter (May to August). The mean total mortality rate (Z) estimated from catch curves and Butterworth et al (1989) equation was 0.72 yr⁻¹ for B. aeneus, 0.62 yr⁻¹ for L. capensis and 1.32 yr⁻¹ for O. mykiss. The estimate of natural mortality was 0.41 yr⁻¹ for both B. aeneus and L. capensis and 0.81yr⁻¹ for O. mykiss.