Dissertations / Theses on the topic 'Clarias gariepinus - Effect of insecticides on'

PhD
An important component of fish health is an optimally functioning reproductive system. The Luvuvhu River Catchment in the Limpopo Province, South Africa, is a tropical, high-risk malaria area where 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT), an endocrine disrupting chemical (EDC), has been used annually since 1945 as a malaria vector control. DDT is known to affect testes morphology and motility of fish sperm. As such, testicular histology and sperm motility (kinematic) parameters were studied as reproductive indicators of the reproductive capacity for two wild, indigenous fish species (Oreochromis mossambicus and Clarias gariepinus) from the currently DDT sprayed area. Three field studies were carried out over two years (2007 – 2008), including two high flow (HF) periods and one low flow (LF) period [HF 1 (March 07), LF (October 07), HF 2 (February 08)]. Both species were sampled from three sites on the Luvuvhu River for testicular histology and computer assisted sperm analysis (CASA), during all three field studies. The sites included a reference site outside the DDT sprayed area, Albasini Dam (AD), and two exposed sites within the DDT sprayed area, Xikundu Weir (XW) and Nandoni Dam (ND). CASA, based on open-source software, was used for the first time in South Africa to assess sperm kinematic parameters of indigenous fish species in field conditions. These included percent motile sperm (% MOT), curvilinear velocity (VCL μm s-1), velocity of an average path (VAP μm s-1), straight line velocity (VSL μm s-1), linearity (LIN %), progression (PROG μm), and average efficiency (AVE. EFF.). Water and sediment samples were collected during all field studies from the three sites for metal and EDC analysis. Controlled laboratory studies were also carried out on the sperm of both species, externally sourced from aquaculture farms equipped to breed and raise fish in toxicant free water. The laboratory studies involved in vitro exposure of spermatozoa to two different, but environmentally relevant, concentrations of both DDT (DDT 1: 0.27 μg L-1; DDT 2: 0.5 μg L-1) and 1,1-dihloro-2,2-bis(p-chlorophenyl)ethylene (DDE) (DDE 1: 0.11 μg L-1; DDE 2: 1.0 μg L-1) with the aim to provide data to support the possible outcomes found in the field studies using CASA. Furthermore, peroxidation of sperm lipids was assayed by production of malondialdehyde (MDA) after in vitro exposure of spermatozoa to DDT and DDE. DDT and its metabolites were found in varying concentrations in the water from all three sites (0.1 μg L-1 – 1.2 μg L-1). Levels of dieldrin (3.5 μg L-1) and lindane (9.4 μg L-1) residues were also found at XW in HF 2. The histological results revealed alterations to testis tissue of both species at all three sites. The testes were assessed through the identification of alterations and an organ index was calculated: Testes Index (IT). The index is indicative of the histological response in the respective tissue type. O. mossambicus at XW had the highest mean IT value during LF (7.45 ± 5.73) and for all field studies combined (5.47 ± 4.63), primarily due to the occurrence of testicular oocytes (intersex), where the frequency of prevalence was 72.73% and 58.82% respectively. These results were statistically higher than the laboratory control (C) group. The CASA results showed statistical differences primarily for O. mossambicus, where motility parameters were lower at XW when compared to AD. Laboratory exposures found a decrease in sperm motility (% MOT) between the control (C) group and the DDT 1, DDE 1 and DDE 2 exposed groups for C. gariepinus. No significant differences were seen for lipid peroxidation (MDA). On the other hand, no significant differences were seen in CASA parameters between the control and exposed laboratory groups for O. mossambicus, but there was an increase in MDA production from the control to the DDT 1 exposure group.

M.Sc.
Sperm, eggs, free embryos and larvae of the sharptooth catfish, Clarias gariepinus, were used in a series of experiments conducted with zinc and copper salts in a flow-through exposure system. Metal concentrations ranged between 0 to 9mg/1 water. The aim of the study was to determine which of these early life stages was the most sensitive towards these metals and to determine whether the early life stages of the sharptooth catfish could be used for rapid bioassesment studies. Parameters investigated were sperm quality, egg hatchibility, free embryo and larval survival and growth. Within all the parameters tested sperm quality proved to be the least sensitive, with no significant changes noted at the metal concentrations used. There are notable reductions on hatching success embryonic and larval survival and growth as metal concentrations increased. Results revealed that the most sensitive was the free embryo stage directly after, and up to 48 hours after hatching. 48 hour old free embryo displayed 48th L.C.50 values as low as 1.98mg/l for zinc and 0. 0.13mg/l for copper, which indicated that this stage was very sensitive and susceptible to environmental stressors. Since C. gariepinus is an indigeniuos species that is widespread throughout the African continent and considering the sensitivity of the early life stages it is a succesfull candidade for use in rapid bioassessment tests throughout the continent.

M.Sc.
A lot of research in ecotoxicology is currently focused on identifying and developing suitable biomarkers for use in assessing the health of aquatic systems. Thus this study was done as part of a major project aimed at identifying and selecting suitable biomarkers to use in the Rietvlei System, South Africa. This study focused on the response of Clarias gariepinus (Burchell, 1822) to contaminants using three biomarkers: population genetic structure, DNA damage and metallothioneins (MT¡¦s). The main objectives of the study were to assess the potential of these biomarkers in C. gariepinus and to provide baseline data on the Rietvlei System. Eighteen enzyme loci (creatine kinase (Ck), esterase (Est), phosphoglucomutase (Pgm), glycerol-3-phosphate dehydrogenase (G3pdh-1 and -2), glucose-6-phosphatase isomerase (Gpi-A and -B), L-lactate dehydrogenase (Ldh-A and B), malate dehydrogenase (sMdh-1, -2 and -3), malate dehydrogenase (NADP+) (Mdhp), phosphogluconate dehydrogenase (Pgdh), isocitrate dehydrogenase (NADP+) (Idh); superoxide dismutase (Sod), and peptidase: substrate (leucyl tryrosine) (Pep-S1 and -2)) were screened for by horizontal starch gel electrophoresis. An agarose gel electrophoretic method was used for DNA damage determination and a spectrophotometric method for metallothionein. The Rietvlei System population (RSP) showed higher genetic variability as shown by the average number of alleles per locus (A), proportion of polymorphic loci (P) and expected average heterozygosity (HE) than the reference populations. Statistically significant deviations (p < 0.05) from Hardy-Weinberg proportions associated with heterozygote deficiencies occurred at Gpi-B, Idh, Pgdh, Ldh-A and Pep-S1 for RSP. These deviations could have been a result of small sample size. There was high genetic differentiation between RSP and the reference populations with FST values of 0.450 and 0.480 between RSP and wild population (WP) and RSP and Northern Cape population (NCP) respectively. A mean base-pair length of 6770.9 „b 10.68 (SE) bp was recorded in the Marais Dam population (MDP) that of 6327.2 „b 17.69 (SE) bp was recorded in the Rietvlei Dam population (RDP). The MDP had a higher proportion of DNA fragments with low base-pair lengths than RP indicating a higher level of DNA damage. The level of DNA damage in the MP was higher than in the RDP. The mean MT¡¦s content was 3.63 „b 0.643 (SE) nmol g-1 wet weight in the MDP and 4.35 „b 0.580 (SE) nmol g-1 wet weight in the RDP. There was no significant (p = 0.40) difference in the levels of MT¡¦s between the two dams. It was concluded that there were significant differences in genetic diversity between RSP and the other populations in unpolluted sites; hence genetic diversity in C. gariepinus has potential as biomarker of pollution. However, further research is recommended to investigate possible contributing factors to differences in genetic diversity such as inter-sex males, geographical isolation and differences in sample sizes used. DNA damage is also a potential biomarker provided due care is taken in interpreting average base-pair length data to consider differences in each DNA size class. It seems further research is required before conclusions are made about use of MT¡¦s as biomarker in this population. The levels of MT¡¦s in other uncontaminated systems will be useful to determine whether the levels recorded in this study are background levels or responses to contamination.
Prof. F.H. van der Bank

D.Phil.
The endocrine system regulates important physiological processes in an organism. Numerous natural and synthetic chemicals are released into the environment and can disrupt the normal functioning of the endocrine system, influencing physiological processes even at relatively low concentrations. These chemicals are known as endocrine disrupting chemicals (EDCs). These compounds are highly persistent in nature due to a resistance to biodegradation, and because of their hydrophobicity. EDCs bio-accumulate especially in the fatty tissue of aquatic and terrestrial organisms. Developmental and reproductive disorders are potentially harmful effects of exposure. EDC sources include agricultural and urban runoff, and industrial effluent discharges that eventually pass through sewage- and wastewater treatment plants. These chemicals degrade at various rates and to varying extents during treatment processes, forming many new chemicals. Methods to predict the occurrence of endocrine disruption include the occurrence of intersex, and changes in spermatogenesis and secondary sexual characteristics (SSCs) of supposedly exposed organisms. The urogenital papilla (UGP) is a SSC whose development and morphology is hormonally controlled and may be influenced when exposed to EDCs. The sharptooth catfish (Ciarias gariepinus) is often used in environmental toxicity studies. Sex is determined by the external dimorphic UGP found only in males. Intersex has been observed in this species in South African freshwater systems. A field study was carried out in the Rietvlei (RVD) and Marais (MD) dams in the Rietvlei Nature Reserve (RNR). MD acts as a sedimentation dam before water enters RVD, and is theoretically more polluted. The RNR system receives effluent from various domestic and industrial sources including agriculture, industries, informal settlements and municipal sewage treatment plants. Four sampling surveys, two low and two high flow, were carried out over a period of two years. Supposedly male catfish (n=97) were collected and identified as male or possible intersex based on the UGP. Water and sediment was collected for target EDC and endocrine disrupting metal (EDM) analyses. Fish length and mass, and UGP length and width were measured. Laparotomy was performed and gonads were inspected macroscopically for alterations. A section of the gonad and the entire UGP was removed and processed according to standard techniques for histological analysis. The gonadosomatic- (GSI), hepatosomatic- (HSI) and UGP length (UGPLI) indices were calculated. Fish fat was removed and analysed for target EDCs.

M.Sc. (Zoology)
The freshwater indicator fish species, Clarias gariepinus, was used to assess and compare the health status of fish from the Hartbeespoort Dam (HBPD) and the Groot Marico Bosveld Dam (GM) which was used as a reference site. HBPD is known to be polluted and renowned for its extreme eutrophic state. GM receives water from the Marico River and is said to be in an unmodified natural ecological state. Adult Clarias gariepinus were sampled using gill nets; during low-flow (n=17) and high-flow (n=20) seasons from the HBPD, and once from the GM (n = 20). A histology-based fish health assessment was done using a necropsy based health assessment index and a qualitative and semi-quantitative histological assessment on selected target organs namely the gills, liver, kidney and gonads. Focus was also placed on reproductive health aspects by staging the gonads according to their reproductive development and assessing the motility of activated sperm using computer assisted sperm analysis (CASA). Water samples were analyzed for selected physical parameters and for selected metals. The results showed distinct macroscopic differences in the livers and testes comparing the two sites. Fish from HBPD had fatty livers and the macroscopic morphology of the testes showed abnormalities regarding the interstitial tissue, possibly due to the proliferation of connective tissue. The macroscopic abnormalities of the livers were reflected in the histological assessment, which concluded steatosis, vacuolation, hepatocyte nuclear alterations and the presence of large numbers of melanomacrophage centers (MMCs). Of these alterations, only MMCs and intracellular deposits were found in fish from the GM. When comparing the HBPD low-flow (LF) and high-flow (HF) sampling trips, the fish from the low-flow had more alterations present in all organs. While the CASA results showed that the motility, velocity and progression of sperm were lower in fish from the HBPD for all parameters, results from GM showed the ideal trend expected from the moment of sperm activation until degeneration. The velocity and progression were significantly (p value <0.05) different between HBPD samples and fish from the GM. The water quality showed increased concentrations of selenium, as well as the endocrine disrupting chemicals (EDCs) nonylphenol and di-n-butyl phthalate. According to the selected parameters assessed, it seems like the water of the HBPD has increasing detriment upon fish health.

M.Sc. (Zoology)
The necessity to maintain high water quality standards has become essential not only to man, but also to conserve aquatic life forms. The Olifants, Selati and Letaba Rivers were monitored for water quality variables and metal concentration in water, sediments and muscle, gill, fat, gonads, liver, bile, blood and kidney of the sharp tooth catfish, C. qariepinus. Some of the water quality variables measured were not within the limits of those standards set for the protection of fish and other aquatic life forms. Turbidity seems to be the biggest problem, due to the Phalaborwa barrage. Metal concentrations were found, in descending order, highest in the sediment, fish and water. This pose the problem of metals being reintroduced into the water column when physico-chemical conditions are not favourable. Experimental studies were done with copper on adult C. qariepinus, due to the extensive copper mining activities in the Phalaborwa region. Haematological and enzymatic analyses revealed a interference in metabolic activity after 96 hour copper exposure. Histological studies on the gill morphology, showed an alteration in the structure with a resultant change in respiratory and osmoregulatory function. LC-50 values were determined for adult and juvenile C. qariepinus in order to set new standards for the protection of aquatic lite in a rapidly developing South Africa.

Water resources are frequently under inspection as pollution increases. Therefore an urgent need has arisen for sensitive bio-monitoring tools in toxicant impact assessment to indicate the effect of pollution on fish health in polluted aquatic ecosystems. Histopathological assessment of fish tissue allows for early warning signs of disease and detection of long term injury in cells, tissues or organs. Various biochemical and biological studies of fish have been used to assess the consequences of environmental toxicants on fish, but histology is able to enhance and add quality to the research carried out by identifying cellular alterations and quantifying the results. The aim of this study was to assess the degree of pollution in the Marais Dam (MD) and Rietvlei Dam (RVD) in the Rietvlei Nature Reserve (RNR) by determining the health status of the sharptooth catfish, Clarias gariepinus, using fish histology as a bio-monitoring tool.The MD and RVD situated within the Sesmyl Spruit serve to provide the area with water and are separated by a natural wetland. The dams were chosen for their elevated levels of toxicants. Four sampling surveys, two low flow and two high flow, were carried out over a period of two years. During each survey twenty fish were sampled per dam. Water and sediment were sampled for metal and endocrine disrupting chemical analysis. A standardized health assessment protocol employed to determine the effects of the toxicants included analysis of blood constituents, fish necropsy, calculation of condition factor and organosomatic indices, and a qualitative and quantitative histological assessment of three target organs: the gills, liver and gonads. These organs were removed and processed according to standard techniques for histological assessment. Histopathological alterations of each organ were identified (qualitative assessment) and subsequently quantified by means of a standard methodology of criteria to assess and compare fish health (quantitative assessment). The total index (Tot-I) values from the quantitative histological assessment were statistically analyzed using the ANOVA method. Potential endocrine disrupting chemicals and metals in the water of both dams were present at levels that could be toxic. The degree of pollution was more severe in MD than RVD. Examination of tissue from the gills, liver and gonads revealed marked histopathological alterations. The quantitative histological assessment indicated that fish collected from MD were in a significantly more severe histopathological condition than those of RVD. These results indicate that the wetland may still function as a natural filter. The qualitative and quantitative histological assessment objectively compared C. gariepinus specimens from MD and RVD and the effects of the toxicants on the health of the fish.
Dr. G.M. Pieterse

M.Sc.
The Vaal Dam subcatchment is located in the upper reaches of the Vaal River. As a result the water quality is reasonably good. In contrast the Vaal River Barrage catchment includes the PWV area, resulting in poorer water quality. During this study, a fish Health Assessment Index (HAI) successfully tested in previous studies on the Olifants River System was applied to the Vaal River System. The aim was to determine if the HAI could distinguish between the Vaal Dam and Vaal River Barrage with regards to water quality. Surveys were conducted bimonthly from November 1998 to February 2000. Physical water quality variables were measured. Water and sediment samples were also collected and analyzed (Institute for Water Quality Studies, Department of Water Affairs and Forestry) to verify the HAI results. Rand Water Board and the Department of Water Affairs and Forestry also made water quality data available. Twenty sharptooth catfish, Clarias gariepinus, were collected from both localities with the aid of gill nets. Fish were checked for external parasites on the boat. On land fish were weighed and measured, after which blood was drawn and slime smears made. Blood and slime smears were examined under a light microscope for parasites. The HAI examination was performed after severing the spinal cord. Internal parasite numbers were recorded. From the parasite data collected infestation statistics were calculated. Four variations of the Parasite Index (PI) were incorporated in the HAI and results compared. During each survey gill arch, gill filament, muscle, skin and liver tissues were collected from each fish. These were analyzed for strontium, aluminium, chromium, manganese, iron, lead, copper, zinc and nickel concentrations using atomic absorption spectrophotometry. Differences in water and sediment trace metal concentrations between localities were small. Metal concentrations in fish tissues recorded from both localities were also almost identical. Possible explanations for this trend were discussed in the relevant section. Highest metal concentrations were generally recorded in gill tissue followed by liver, skin and muscle. Physical water quality variables (salinity and conductivity), and macro water analysis (e.g. phosphate and nitrate) indicated that water quality at the Vaal River Barrage was poorer. The HAI confirmed this. Higher index values were recorded from the Vaal River Barrage, with the converse being true for the Vaal Dam. Regression analysis indicated that plasma protein, haematocrit and the index value obtained using the Inverted Parasite Index, most successfully predicted (70 %) from where a randomly chosen fish were collected. When viewing index values obtained using the four versions of the PI, all four distinguished between localities. The discriminatory ability of the Inverted PI was slightly higher than that of the other PI's. It is concluded that the HAI distinguished successfully between the Vaal Dam and Vaal River Barrage on the grounds of water quality. Poor fish health correlated with decreasing water quality (salinity and eutrophication).

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.

M.Sc.
This study aims to assess the potential impacts of intense feedlot activity on the aquatic freshwater environment, with reference to three feedlots, ranging in production size and all situated in the upper Vaal catchment area. Field assessments were done over a high flow and low flow period, while controlled exposures were also done to quantify a potential stress reaction to growth hormone exposure (using Clarias gariepinus as test organism). It was ascertained that water quality variables contributing towards differences between upstream and downstream environmental conditions are NH4 concentrations pH and conductivity. Lead concentrations were also periodically higher downstream from feedlot activity, in comparison with upstream. Taking the sediment assimilation potential of growth hormones into consideration, it was determined that Feedlot C showed the highest assimilation potential, while Feedlot A reflected the lowest. Alterations on family level invertebrate community structures indicated a categorical decline in abundances and species richness at sites situated downstream from feedlots. However, some clear seasonal influences were also observed. Further community and diversity analyses reflected alterations in invertebrate community structures that were not reflected in SASS 5 scores. With regards to the biomarkers applied in this study, it was noted that there was a significant (p<0.05) difference in the cellular energy allocation (CEA) between control and hormone exposed groups. The total amount of energy available (Ea) increased significantly for test organisms exposed to Diethylstilbestrol (DES), while there was a significant increase in energy consumption (Ec) of test organisms exposed to Trenbolone acetate (TBA). In addition to CEA, metabolic profiling of blood plasma was also performed, which indicated a definite ordination in metabolic constituents after fifteen days of exposure. This was established by subjecting the data to principle component analysis (PCA), which accounted for 83 % variance observed. The impacts and biotic responses identified in this study were contextualised with known literature on the effects of feedlot activity and growth hormone exposure on the aquatic environment. Finally, conclusions were drawn and recommendations made with regard to improving feedlot operational activities. The results obtained in this study contribute towards an integrated framework for the environmental management of feedlot activities.

M.Sc. (Aquatic Health)
South Africa’s freshwater ecosystems are under threat due to anthropogenic activities. Recent reports have shown that the Hartbeespoort- (HBPD), Klipvoor- (KD) and Bospoort Dam (BD) impoundments situated in the North-West Province are polluted as a result of mining, industrial and agricultural activities. These impoundments are classified as being in a hypertrophic state. The health status of fish in these impoundments is of concern, and needs to be investigated. For this purpose, Clarias gariepinus and Cyprinus carpio were collected for a histology-based fish health assessment. These two species are present in the selected dams and are some of the preferred fish species for human consumption by the local people. The aim of the study was to determine the health status of these fish species in HPBD, KD and BD using a semi-quantitative histopathological assessment on selected target organs and compare the results to fish from a reference site, the Marico-Bosveld Dam (MBD). Gill nets were used for the collection of specimens. Fish were macroscopically examined, weighed and measured for the calculation of the condition factor. Blood samples were collected for haematocrit, leukocrit and total protein determination. Once sacrificed, a necropsy-based health assessment (HAI) was performed to determine any abnormalities within the visceral cavity. The selected target organs were excised and weighed for the calculation of selected biometric indices. Collected tissue samples were processed using standard histological techniques and the prepared slides were stained using Haematoxylin and Eosin. Macroscopically, a number of fish from polluted sites exhibited liver with fatty change and focal discoloration as well as severe parasites within the visceral cavity. As a result, higher HAI values were recorded in polluted sites compared to the reference site. The haematocrit values varied from normal to below and above the normal range. Leukocrit values were within the normal range except for C. gariepinus from HBPD, which was above the normal range. Total protein values were within the normal range for both species for all sites. The condition factor and hepatosomatic index (HSI) values were within the accepted range except for the HSI of C. gariepinus from MBD. The mean organ index for all study sites fell within class 1 with the exception of the liver index from HBPD, KD and BD which was in class 2. Class 1 (index value <10) is indicative of slight histological alterations while class 2 (index value 10-25) translates to moderate histological alterations. Overall, a higher prevalence of histopathological alterations was noted among fish from polluted sites compared to fish from the reference site. Hence, on the basis of the macroscopic and histopathological results, the fish from the polluted sites were more affected in terms of these parameters compared to fish from the reference site. The results therefore provide valuable information for future bio-monitoring studies in the HBPD, KD and BD impoundments.

Ph.D. (Zoology)
Histomorphology as a tool to assess the health status of five economically important fish species in the Okavango Delta Panhandle, Botswana the Okavango Delta, and an inland freshwater wetland of national and international importance was designated by the Ramsar Convention in 1996. This site is of global importance because of a wide diversity of fish species found in this freshwater ecosystem. The Okavango Delta is also one of the last 'near pristine' sites on the African continent and therefore serves as an ideal reference site to describe the normal histomorphology of selected organs in sentinel fish species which could be used as reference for future toxicological studies. The aim of this study was to assess the health status of five economically important fish species namely, Clarias gariepinus (Burchell, 1822), Clarias ngamensis (Castelnau, 1861), Serranochromis robustus jallae (Gunther, 1864), Serranochromis angusticeps (Boulenger, 1907) and Hydrocynus vittatus (Castelnau, 1861) sampled from the Okavango Delta Panhandle, by describing the normal histomorphology of the liver, gills and gonads of the sentinel species. The sentinel fish species are of significant importance because they form an integral part of the small-scale commercial, subsistence and recreational fisheries in this ecosystem. In the past few decades, fish-health research has focused almost exclusively on histopathological alterations resulting from pollution caused by exposure to chemicals, parasitesand pathogens. Limited attention has been devoted to the normal histomorphology and health status of fish species in various aquatic ecosystems including the Okavango Delta Panhandle. Also, histopathological evaluations noted only the presence of abnormalities without quantitative assessment of the extent of the abnormalities within each tissue section. The absence of baseline normal histomorphology and numerical data however, makes it difficult to establish cause-and-affect relationships between pathology and contamination patterns in various fish species. It is imperative therefore, that the normal histomorphology of organs in fish species occurring in this region should be known so that histopathological conditions maybe accurately diagnosed…

Ph.D.
The current study evaluated a bio-monitoring technique developed in the USA by Adams, Brown and Goede, 1993. This project was sponsored by the Department of Water Affairs and Forestry (DWAF), to enable testing of the Health Assessment Index (HAI) under South African conditions. Testing took place in the Olifants River system, one of the most polluted river systems . in South Africa. Initially two river points were tested using Oreochromis mossambicus (Robinson, 1996), Clarias gariepinus (Marx, 1996) and Labeo rosae (Luus-Powell, 1997). The current study re-tested the HAI at the same two sample sites, namely Mamba and Balule in the Kruger National Park, using 0. mossambicus and C. gariepinus respectively. Two additional sites were tested in the upper catchment area, namely Loskop Dam and Bronkhorstspruit Dam. The current study further enabled the comparison of HAI results collected during drought and flood conditions. Results obtained after deployment of the HAI were corroborated using chemical analysis of water, sediment and biota. Water and sediment analysis was carried out by the Institute for Water Quality Studies using standard techniques. Bio-accumulation of aluminium, copper, iron, lead, manganese, nickel, strontium and zinc was assessed in the gills, liver, skin and muscle tissue of sample fish using standard Atomic Absorption Spectrometry techniques. Modifications made to the original HAI involved the inclusion of variable ranking in the assessment of fish parasites, with endo- and ectoparasites evaluated separately. Testing of this parasite hypothesis lead to the development of a Parasite Index component to the HAI. Assessment of water, sediment and fish tissue determined that the Olifants River system is indeed exposed to macro and heavy metal pollutants, which negatively affect aquatic health. Constituents posing the greatest threat are chlorides, fluorides, phosphates, total dissolved solids, copper and iron concentrations. Testing the HAI and parasite hypothesis using C. gariepinus, provided the most meaningful results. During testing of the parasite hypothesis both endo- and ectoparasite numbers conformed to the suggested idea that higher endoparasite numbers will occur at highly impacted areas, whereby ectoparasite numbers will be low. This was particularly evident in the lower catchment area, whereby comparisons between drought and flood conditions were carried out. Subsequent decreases in water quality directly after the flood were noted using water and sediment analysis. This observation reflects the results gathered using the HAT and during testing of the parasite hypothesis at all four sample sites. During statistical analysis of the HAI, using logistic regression analysis, parasite numbers, more specifically endoparasite numbers, were the most indicative of fish health. Environmental stressors (flood conditions) result in immunological responses observed in fish, and are reflected statistically using the HAI as changes in WBC %. It is suggested that endoparasites and WBC % provide the best overall assessment of fish condition. These variables should thus not be eliminated, in order to streamline the HAI evaluation procedures. Testing of this bio-monitoring technique under South African conditions provided meaningful results. This indicates that the HAI can be used to assess water quality, with existing water monitoring programmes further benefiting from its incorporation.

M.Sc. (Zoology)
The Vaal River system is constantly subjected to pollution from various industrial, mining and agricultural activities. Consequently, pressure is continually exerted on the health of its fish communities and it was suspected that this may be a contributing factor to the repeated fish kills that have occurred in various sections of the river over the past few years. The aim of this study was to assess the health status of three fish species that were affected by the most recent mass fish mortality in the Vaal River. This was done using a combination of techniques including a histology-based health assessment (HHA) that involved a standard fish necropsy, the evaluation of blood parameters as well as a microscopic assessment of the liver, kidney, gills, and gonads. The histological results were semi-quantitatively assessed. Selected chemical substances were also tested for in water, sediment and the skeletal muscle tissue of the fish. Clarias gariepinus, Labeo capensis and Labeo umbratus specimens were collected from the Vaal River, approximately 2480m below the Vaal Dam (Latitude 26°51'17.47"S; Longitude 28° 7'16.58"E) following the latest occurrence of a fish kill in November 2011. Fish were collected using gill nets. Water was sampled in triplicate at three locations, and in situ measurements were done for selected physico-chemical parameters. Sediment samples were also collected and subjected to a sequential extraction technique and quantification of the heavy metals was done using Inductively Coupled Plasma-Mass Spectroscopy (ICP-MS). Metals in skeletal muscle tissue and water were quantified using the same technique. An analysis of variance (ANOVA), followed by the appropriate post-hoc test was performed to determine differences between means of variables i.e. morphometric, histological, substance concentration and blood parameters...