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Historical biogeography of the tribe Platypleurini Schmidt, 1918 (Hemiptera: Cicadidae) with a focus on Southern Africa

  • Authors: Price, Benjamin Wills
  • Date: 2010
  • Subjects: Biogeography -- History -- Africa, Southern Cicadas -- Africa, Southern Cicada (Genus) -- Africa, Southern Biodiversity -- Africa, Southern Cicadas -- Variation -- Africa, Southern
  • Language: English
  • Type: Thesis , Doctoral , PhD
  • Identifier: vital:5708 , http://hdl.handle.net/10962/d1005394
  • Description: With our contemporary biota under increasing threat of extinction, it is of interest to understand where, why and how biological diversity is generated. If focussed on appropriate taxa, phylogeographic and phylogenetic studies can assist in the identification of both places and processes central to the origin and maintenance of biological diversity. It is explained why southern Africa presents a perfect test-bed for exploring such mechanisms of diversification and why cicadas (Hemiptera: Cicadidae) have proved very suitable tools for studies of historical biogeography. This study then exemplifies these points by providing the first large-scale investigation of the historical biogeography of the tribe Platypleurini Schmidt, 1918, with emphasis on the genus Platypleura Amyot & Seville, 1843 in southern Africa. Standard methods of DNA sequencing provided data from portions of the mitochondrial small subunit ribosomal 16S RNA (16S) and cytochrome oxidase subunits I (COI) and II (COII); and the nuclear elongation factor 1 alpha (EF-1α) from 400 ethanol-preserved specimens. These data were analysed using standard phylogenetic methods and a time scale of diversification was estimated using a Bayesian framework and both fossil data and DNA substitution rates. The results showed that the tribe is too recent to be of Gondwanan origin. The lack of monophyly of the genera represented in both Asia and Africa showed that the tribe needs formal taxonomic revision. Diversification of the African platypleurine genera coincides with aridification in the early Oligocene. Dispersal of Asian platypleurine taxa coincides with the meeting of Africa and Eurasia in the mid-Oligocene. Two radiations within African Platypleura are hypothesised; one distributed over most of sub-Saharan Africa and the second restricted to southern Africa, with clades restricted within regional biomes. Within each of the three focal biomes, cryptic taxonomic diversity was confirmed, suggesting that, even in relatively well understood groups such as the southern African platypleurine cicadas, molecular data can identify further diversity. Although each focal taxon was restricted to non-overlapping biomes, comparison of the three biomes highlighted interactions between palaeoclimates and fixed landscape features (coastal topography, river catchments and escarpments) as causative agents of vicariance, dispersal, extinction and diversification of these volant insects. The results of using co-distributed species for comparative study cautions against making inferences based on single-taxon datasets and highlights the need to use many, evolutionarily independent taxa when identifying mechanisms of diversification. The dating analyses imply that within-species lineage diversification occurred overwhelmingly within the Pleistocene, a trend that is being increasingly recognised in print for other biota. Some caveats about using phylogenetic approaches to estimate ancestral areas are illustrated. Several recommendations are made regarding additional taxa and data sources for understanding the origin and maintenance of biological diversity.
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  • Date Issued: 2010

Understanding workplace-based learning contexts to inform curriculum development: the case of a Level 5 Environmental Education, Training and Development Practice Qualification

  • Authors: Wigley, Jonathan James
  • Date: 2006
  • Subjects: South African Qualifications Authority National Qualifications Framework (South Africa) Environmental education -- Study and teaching -- South Africa Curriculum planning -- South Africa Competency-based education -- South Africa Vocational qualifications -- South Africa Education and state -- South Africa Education -- Standards -- South Africa Education, Higher -- South Africa -- Standards
  • Language: English
  • Type: Thesis , Masters , MEd
  • Identifier: vital:1808 , http://hdl.handle.net/10962/d1003694
  • Description: This is an interpretive case study that explores the workplace epistemologies and institutional structures of two nested cases within the broader context of the Environmental Education, Training and Development Practices - Level 5 qualification (EETDP qualification) that is registered on the South African National Qualifications Framework. The study provides insights to inform EETDP curriculum development that is enabling of reflexive environmental education and training processes. The study develops an understanding of workplace epistemologies related to environment and education, the structural factors that enable and constrain agency of environmental educators and the role of reflexivity in practice and in education in two nested cases: the agricultural and local government sectors. It draws on findings from workshops, semistructured interviews and document analysis of education materials in these two nested cases. The study notes that there are diverse and seemingly ambiguous understandings of both environment/sustainability and education processes in the two nested cases. This ambiguity seems to relate to environmental education practitioners drawing on different forms of knowledge, including differentiated or theoretical knowledge, and 'common-sense' ways of knowing, in their education practice. The understandings related to theoretical knowledge are, in both nested cases, dominated by scientific or technical understandings where environment is understood in the terms of the natural sciences and education is seen in instrumentalist terms as the transfer of mainly technical environmental knowledge to learners in order to effect behaviour change. The study opens up deeper understandings of the epistemological, socio-cultural and structural features of context, in the two nested cases, that have a bearing on environmental educators. It provides insights into workplace structures that can be both enabling and constraining of agency and notes that the causal power of structures to enable or constrain does not lie only in the structures but also in relation to the intentionality of the environmental education practitioners/agents. The study then examines reflexivity as one of the means through which environmental educators in the nested cases are able to consider appropriate actions or responses to structural constraints or enablements. Based on the insights offered by the research findings, the study makes recommendations for the EETDP curriculum development. It frames these recommendations within an understanding of curriculum as a contextualised social process that involves structural aspects of curriculum such as materials, as well as socio-cultural processes such as learning on the course and in the workplace.
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  • Date Issued: 2006

Molecular characterization of the tetratricopeptide repeat-mediated interactions of murine stress-inducible protein 1 with major heat shock proteins

  • Authors: Odunuga, Odutayo Odutola
  • Date: 2003
  • Subjects: Plants -- Effect of stress on Proteins -- Purification Electrophoresis Heat shock proteins
  • Language: English
  • Type: Thesis , Doctoral , PhD
  • Identifier: vital:4091 , http://hdl.handle.net/10962/d1007724
  • Description: Murine stress-inducible protein 1 (mSTI1) is a co-chaperone that is homologous with the human heat shock protein 70 (Hsp70)/heat shock protein 90 (Hsp90)-organizing protein (Hop). The two proteins are homologues of the highly conserved stress-inducible protein 1 (STI1) family of co-chaperones. The STI1 proteins interact directly and simultaneously at some stage, with Hsp70 and Hsp90 in the formation of the hetero-multi-chaperone complexes that facilitate the folding of signal transducing kinases and functional maturation of steroid hormone receptors. The interactions of mSTI1 with both Hsp70 and Hsp90 is mediated by a versatile structural protein-protein interaction motif, the tetratricopeptide repeat (TPR). The TPR motif is a degenerate 34-amino acid sequence a-helical structural motif found in a significant number of functionally unrelated proteins. This study was aimed at characterizing the structural and functional determinants in the TPR domains of mSTI1 responsible for binding to and discriminating between Hsp70 and Hsp90. Guided by data from Hop's crystal structures and amino acid sequence alignment analyses, various biochemical techniques were used to both qualitatively and quantitatively characterize the contacts necessary for the N-terminal TPR domain (TPR1) of mSTI1 to bind to the C-terminal EEVD motif of heat shock cognate protein 70 (Hsc70) and to discriminate between Hsc70 and Hsp90. Substitutions in the first TPR motif of Lys⁸ or Asn¹² did not affect binding of mSTI1 to Hsc70, while double substitution of these residues abrogated binding. A substitution in the second TPR motif of Asn⁴³ lowered but did not abrogate binding. Similarly, a deletion in the second TPR motif coupled with a substitution of Lys⁸ or Asn¹² reduced but did not abrogate binding. Steady state fluorescence and circular dichroism spectroscopies revealed that the double substitution of Lys⁸ and Asn¹² resulted in perturbations of inter-domain interactions in mSTl1. Together these results suggest that mSTI1-Hsc70 interaction requires a network of electrostatic interactions not only between charged residues in the TPR1 domain of mSTI1 and the EEVD motif of Hsc70, but also outside the TPR1 domain. It is proposed that the electrostatic interactions in the first TPR motif collectively made by Lys⁸ and Asn¹² define part of the minimum interactions required for successful mSTI1-Hsc70 interaction. In the first central TPR domain (TPR1A), single substitution of Lys³°¹ was sufficient to abrogate the mSTI1-Hsp90 interaction. Using a truncated derivative of mSTI1 incapable of binding to Hsp90, residues predicted by crystallographic data to determine Hsp70 binding specificity were substituted in the TPR1 domain. The modified protein had reduced binding to Hsc70, but showed significant binding capacity for Hsp90. In contrast, topologically equivalent substitutions on a truncated derivative of mSTI1 incapable of binding to Hsc70 did not confer Hsc70 specificity on the TPR2A domain. These data suggest that binding of Hsc70 to the TPR1 domain is more specific than binding of Hsp90 to the TPR2A domain. In addition, residues C-terminal of helix A in the second TPR motif of mSTI1 were shown to be important in determining specific binding to Hsc70. Binding assays using surface plasmon resonance spectroscopy showed that the affinities of binding of mSTI1 to Hsc70 and Hsp90 were 2 μM and 1.5 μM respectively. Preliminary in vivo studies revealed differences in the dynamics of binding of endogenous and exogenous recombinant mSTI1 with Hsc70 and Hsp90. The outcome of this study poses serious implications for the mechanisms of mSTI1 interactions with Hsc70 and Hsp90 in the cell.
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  • Date Issued: 2003

The molecular microbial ecology of sulfate reduction in the Rhodes BioSURE process

  • Authors: Chauke, Chesa Gift
  • Date: 2002
  • Subjects: Water -- Purification -- Biological treatment , Acid mine drainage , Water -- Microbiology
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:4082 , http://hdl.handle.net/10962/d1007475 , Water -- Purification -- Biological treatment , Acid mine drainage , Water -- Microbiology
  • Description: The research reported here investigated the use of a Baffle Reactor in order to study aspects of the biological sulfur cycle, where a floating sulfur biofilm formation occurs and where complex organic compounds provide electron donor sources. The development of a laboratory-scale Baffle Reactor model system satisfied the requirements for sulfate reducing bacterial biomass growth and sulfur biofilm formation. Since relatively little is known about the microbial ecology of floating sulfur biofilm systems, this study was undertaken to describe the sulfate reducing sludge population of the system together with its performance. A combination of culture- and molecular-based techniques were applied in this study in order to investigate the microbial ecology of the sulfate-reducing bacteria component of the system. These techniques enabled the identification and the analysis of the distribution of different sulfate reducing bacterial strains found within the sludge bioreactors. Strains isolated from the sludge were characterised based on culture appearance, gram staining and scanning electron microscopy morphology. Molecular methods based on the PCR-amplified 16S rRNA including denaturing gradient gel electrophoresis were employed in order to characterise sulfate-reducing bacteria within the reactors. Three novel Gram negative sulfate-reducing bacteria strains were isolated from the sludge population. Strains isolated were tentatively named Desulfomonas rhodensis, Desulfomonas makanaiensis, and Clostridium sulforhodensis. Results obtained from the Baffle Reactor showed that three dominant species were isolated from the DNA extracted from the whole bacterial population by peR. Three of these were similar to those mentioned above. The presence of these three novel unidentified species suggest that there are a range of other novel organisms involved in sulfate reduction processes.
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  • Date Issued: 2002

Challenges facing probation officers working with young persons in conflict with the law

  • Authors: Volsak, Nobubele
  • Date: 2001
  • Subjects: Probation officers Probation officers -- Attitudes -- South Africa -- Eastern Cape Juvenile delinquents Probation
  • Language: English
  • Type: Thesis , Masters , MSocSc
  • Identifier: vital:710 , http://hdl.handle.net/10962/d1006534
  • Description: This study aimed at focusing on the challenges facing probation officers working with young persons in conflict with the law, in the Eastern region, which forms part of the Eastern Cape Province. The main purpose of the study was to explore the experiences of probation officers in terms of the legislation that they are using when making decisions pertaining to young persons and the types of programmes that they offer to young persons for diversion and prevention purposes. The researcher also wanted to generate a greater understanding of the resources which probation officers have and need in order to run their programmes successfully to young persons, as well as to explore their feelings about working with young persons. The researcher did some literature review in relation to this field, where it became evident that probation services in respect of young persons in conflict with the law, is a relatively new field of specialisation in South Africa. This field started around 1995 as a result of the Inter - Ministerial Committee (IMC) on young people at risk, which was set up to respond and manage the crisis of more than one thousand children who were released from prisons and police cells. The IMC then, identified probation officers as leading role players in dealing with young persons in conflict with the law. An exploratory (non - experimental) design was used to carry out the research. A qualitative research method was also used as it attempts to describe and explain social reality from the points of view of the participants. This is because the researcher was interested to find out the experiences of probation officers in relation to their work with young persons. A non - probability purposive sample of all (11) probation officers was used. A semi - structured interview schedule with both closed and open - ended questions was used to collect data. All the information gathered from those personal interviews, was analysed by hand because the researcher wanted to interpret and produce social explanations. The findings of this small - scale study have revealed that there are a number of challenges facing probation officers. For example presently there is no comprehensive legislation for the management of young persons caught up in the criminal justice system. Instead, limited provisions are spread throughout a number of separate statutes, which make it difficult for probation officers to apply them. This study has also revealed that there is a shortage of human and material resources, which somehow impact negatively on how probation officers render services to their clientele. All probation officers in this study have positive feelings and attitudes about their work despite the fact that there are some challenges facing them that need to be addressed. Specific recommendations have been made based on the findings of this study, which could contribute to the development of probation services in respect of young persons in conf lict with the law
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  • Date Issued: 2001

Ichthyofaunal community structures in different types of Eastern Cape estuaries

  • Authors: Vorwerk, Paul D
  • Date: 2001
  • Subjects: Estuarine fishes -- South Africa -- Eastern Cape , Estuarine fishes -- South Africa
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:5377 , http://hdl.handle.net/10962/d1016241
  • Description: This investigation had three major objectives; firstly to document the estuarine fishes from several poorly studied Eastern Cape estuaries, secondly, to identify similarities and differences in the fish communities from permanently open and intermittently open estuaries, and thirdly, to establish which physico-chemical or environmental variables are responsible for the structuring of these communities. The study area incorporated 10 estuaries along a 70 km long stretch of the Eastern Cape coastline between the towns of Seafield (33° 32' 42" S, 27° 03' 05" E) in the south-east and Hamburg (33° 16' 45" S, 27° 29' 50" E) in the north-west. The systems investigated included two permanently open estuaries and eight intermittently open systems of varying sizes. Overall fish abundance and species richness in the study area revealed no significant seasonal variation. A contrast between open and closed estuaries was evident in the dominance of species from different estuarine dependence categories. Open estuaries comprised mainly category Ib, lla and IIb species, with a high proportion of category IV species. Closed estuaries were dominated by category IIa species, with few category IV species represented. Clear longitudinal trends in relative abundance were demonstrated for individual species. Margalefs species richness index for seine net catches, and a combination of the seine and gill net data, were significantly correlated with catchment size, mean annual runoff, estuarine area and linear length. Fish assemblages in the permanently open and intermittently open estuaries were significantly different (p<0.001) when analysed on a community and density basis. Similarly, the communities in large and small intermittently open estuaries differed significantly on a community (p=0.01) and density basis (p<0.001). These differences where caused by changes in abundance of the dominant estuarine resident and marine migrant species. The environmental variable that was dominant in accounting for these differences was the estuary mouth status. Estuarine resident species had smaller overall body lengths when compared with the marine migrant species. In addition, the estuarine resident species had smaller modal size classes in the closed estuaries when compared with the open estuaries. These differences may be linked to the foraging strategies of the species, as well as food availability and different levels of predation in the different estuary types. The marine migrant species did not show any trends in this respect although the closed systems had the largest individuals for all four dominant marine species. This finding may be linked to the inability of these species to breed in closed estuaries, thus channelling reproductive energy resources into somatic growth. In addition, prolonged periods of mouth closure prevent the emigration of large individuals back to the sea. Otter trawling was conducted in fiye estuaries and captured mostly demersal species. The otter trawl data confirmed the seine net community analysis, with significantly different communities identified in the permanently open and intermittently open estuaries (p=0.02), as well as in the small and large intermittently open estuaries (p=0.03). The environmental variables responsible for these community differences were mouth status and variables associated with estuarine size. The identification of estuary mouth status by this study as the most influential environmental factor is compounded by this "ariable affecting or being indicative of numerous other physico-chemical features. The large differences in the fish communities in different estuary types indicate the importance of each estuary type to various species. This should be taken into account before allowing any form of commercial fishing in these important nursery areas.
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  • Date Issued: 2001

The protein requirements of the South African abalone, Haliotis midae

  • Authors: Shipton, Thomas A
  • Date: 2000
  • Subjects: Abalones -- Nutrition Abalones -- Digestion
  • Language: English
  • Type: Thesis , Doctoral , PhD
  • Identifier: vital:5314 , http://hdl.handle.net/10962/d1005159
  • Description: The potential to reduce feed formulation costs by the replacement of existing proteinsources in artificial feeds for Haliotis midae was assessed. A comparison between the efficacy of the direct method and chromic oxide marker techniques in determining apparent protein digestibility coefficients, revealed that while the former was not a suitable methodology for use with this species, the latter produced replicable and reliable results. It was established that the chromic oxide marker is inert, is not absorbed by the abalone, does not interfere with the digestive processes and moves through the intestine at the same rate to the protein. However, as this method was time consuming and expensive to implement, a multienzyme pH-stat in vitro protein digestibility technique using a three enzyme system was employed to rapidly assess the protein quality of 34 protein sources. The efficacy of the technique was established by correlating the in vitro digestibility estimates with in vivo digestibility coefficients obtained using the chromic oxide marker technique. The highest degree of in vivo predictability was attained when protein sources were separated according to origin, and significant correlations between either animal (r²=0.89, P<0.004) or plant (r²=0.79, P<0.04) protein sources were found. The effect of animal size on the qualitative protein requirements of two size classes of H.midae was assessed by feeding 12 isonitrogenous and isoenergetic single protein diets to juvenile and young adult animals (10-20 and 40-50mm shell length). The criteria for protein source selection were their bioavailability as determined using the pH-stat in vitro digestibility technique, and their cost and availability within South Africa. The protein sources identified for the trial comprised four fishmeals, casein, spirulina, abalone viscera silage, brewery waste, torula yeast, carcass, sunflower and cotton meals. The results indicated that in terms of growth and feed efficiency, the fishmeals and spirulina were the most suitable candidates as primary protein sources in formulated feeds for H.midae, and with the exceptions of the carcass meal and brewery waste, the remaining protein sources demonstrated promise as partial primary protein source replacements. The smaller size class of abalone displayed significantly reduced growth, feed and protein efficiency than their larger counterparts. In terms of feed conversion and growth response, two-way analysis of variance revealed significant interactions between protein source and animal size, suggesting that qualitative differences exist between the dietary protein requirements of the juvenile and young adult abalone. The commercial implication of thisfinding was discussed. An evaluation was undertaken to determine the effects of the partial and total replacement of dietary fishmeal with selected plant protein sources on growth and nutritional indices of juvenile H.midae. A commercial “Abfeed” formulation in which 100% of the protein component comprised LT-fishmeal was employed as a control. Fifteen isonitrogenous experimental diets were formulated in which the LT fishmeal was substituted at either 10, 15, 30, 50, 75 or 100% with either spirulina, semolina, ground maize, torula yeast, soya, sunflower or corn gluten meals or combinations thereof. No significant differences were found in the growth rates between the control diet and those diets in which 30% of the fishmeal component had been replaced by either soya, sunflower meal, or torula yeast. In addition, 50% of the fishmeal component could be substituted with either soya meal or spirulina without affecting growth. Replacement of either 75 or 100% of the fishmeal had a significant negative affect on growth. Pearson product moment correlations between dietary lysine levels and either growth rates or protein efficiency ratios revealed positive correlations (r=0.77, P=0.0005; r=0.52, P=0.04 respectively) suggesting that lysine may have been the first limiting amino acid in these diets. Carcass analysis revealed that dietary protein source had no significant effect on body composition. An assessment of the dietary arginine requirement of juvenile H.midae using whole proteins to supply graded levels of dietary arginine did not promote a growth response. It was concluded that arginine is probably not the first limiting amino acid in formulated feeds for H.midae. An assessment of the dietary lysine requirement of juvenile H.midae using two micro-encapsulation techniques (gelatin/acacia colloid or cellulose acetate phthalate) was not successful. The efficacy of the encapsulation techniques were established and an assessment of the degree of lysine supplementation undertaken. Failure of the crystalline lysine enriched diets to promote growth suggests that the prospects for using crystalline amino acids in essential amino acid requirement studies in H.midae is low. The results of the present study indicate that the prospects for replacing fishmeal with cheaper alternative protein sources in artificial feeds for H.midae is promising. Furthermore, while the technical difficulties such as the determination of the essential amino acid requirements of the abalone precluded the application of “least cost” programming, the prospects for its future application are promising.
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  • Date Issued: 2000

An investigation into cultural differences in the conceptualization of and attributions about cognitive decline in the elderly

  • Authors: Fair, David Alan
  • Date: 1999
  • Subjects: Dementia , Older people , Dementia Case studies
  • Language: English
  • Type: Thesis , Masters , MA
  • Identifier: vital:2974 , http://hdl.handle.net/10962/d1002483 , Dementia , Older people , Dementia Case studies
  • Description: There is little data regarding the prevalence of dementia in South Africa. Estimating such prevalence is problematic as the most commonly used cognitive screening tests are inappropriate for use in non-western populations. For this reason researchers have explored the use of informant questionnaires where relatives provide information on cognitive functioning over the last year. In the South African context Lenger, de Villiers & Louw (1996) conducted a dementia case-ascertainment study in a Xhosa-speaking community near Cape Town using a well-known informant questionnaire, the DECO, and concurrent clinical assessment. Reflecting on the discrepancies between DECO scores and clinical diagnosis, the researchers conducted interviews to explore beliefs and expectations regarding the elderly and cognitive decline. The aims of the current research were to gather comparative data from Bothasig, an English-speaking community, in order to explore areas of commonality and difference in perceptions and attributions regarding cognitive decline in the elderly. The study found that a significant percentage of informants from both Bothasig and Langa consider forgetfulness to be normal in old age. Different discourses around illness in the elderly were identified incorporating a range of medicalised and folk attributions. The discussion showed that informant perceptions within the Langa community may increase the likelihood that observational data provided in informant questionnaires may be confounded by cultural perceptions regarding the elderly. In addition, certain items on the DECO were found to be unsuitable for use across groups and modifications were proposed. The data was analyzed using both quantitative methods and phenomenological discourse analysis. The discussion concluded with metatheoretical reflections on the tension between etic and emic perspectives in cross-cultural research.
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  • Date Issued: 1999

A comparison of the aquaculture potential of Clarias gariepinus (Burchell, 1822) and its hybrid with Heterobranchus longifilis valenciennes, 1840 in Southern Africa

  • Authors: Oellermann, Lawrence Keith
  • Date: 1996
  • Subjects: Aquaculture -- South Africa Clarias Clariidae Catfishes -- South Africa
  • Language: English
  • Type: Thesis , Doctoral , PhD
  • Identifier: vital:5246 , http://hdl.handle.net/10962/d1005089
  • Description: The aim of this study was to evaluate the aquaculture potential of a hybrid between the two largest African silurid catfish, Heterobranchus longifilis (HL) and Clarias gariepinus (CG) . A morphometric, meristic and karyological study showed that the hybrid shared some of the physical characteristics of both C. gariepinus and H. longifilis, while its chromosome complement and fundamental number (2N = 54, FN = 95), was intermediate between that of H. longifilis (2N = 52, FN = 92) and C. gariepinus (2N = 56, FN = 97). The HLxCG cross could therefore be regarded as a true hybrid. For the characters tested, no morphological or karyological differences were apparent between the HLxCG hybrids produced in West Africa and those produced in southern Africa. In southern Africa, the HL♂xCG♀ cross had higher fertilization and hatching rates than pure strain H. longifilis, C. gariepinus or the reverse cross. There was no difference in the survival of the HL♂xCG♀ hybrid larvae and C. gariepinus larvae up to the onset of exogenous feeding. Pure strain H. longifilis juveniles had a faster growth rate than the H. longifilis ♂ x C. gariepinus ♀ juveniles, but the hybrid always grew at a faster rate than C. gariepinus or the reverse cross. The HL♂xCG♀ cross was consequently chosen as the hybrid with the greatest potential for siluroid aquaculture in southern Africa. The HL♂xCG♀ hybrid showed evidence of partial gonadic, gametic and post-zygotic sterility in both sexes. The hybrid was not completely sterile, as it was artificially induced to spawn, and a small number of viable F₂ hybrid and F₁ hybrid x C. gariepinus larvae were produced. However, in the light of its probable reproductive strategy, it is highly unlikely that the hybrid would pose an ecological risk to the southern African region. The H. longifilis ♂ x C. gariepinus ♀ hybrid was compared to C. gariepinus for selected water quality preferences and tolerances. The hybrid had a wider temperature preference (28 °C to 34 °C) than C. gariepinus (28 °C to 30 °C), but appeared to be more dependent on aerial respiration than C. gariepinus. The air-breathing frequency of hybrid fish began to increase at dissolved oxygen concentrations below 3 .8 mg.ℓ⁻¹, while C. gariepinus only showed an increase in air-breathing frequency at concentrations below 3.0 mg.ℓ¹. The hybrid was more tolerant of un-ionised ammonia (96-hour LC₅₀ = 9.1 mg.ℓ⁻¹) than C. gariepinus (96-hour LC₅₀ = 6.5 mg.ℓ⁻¹), but their 96-hour LC₅₀ salinity tolerances were similar (10.8-11.0 g.ℓ⁻¹). The H. longifilis ♂ x C. gariepinus ♀ hybrid had a higher fillet yield (43.9 %) than C. gariepinus (38.9 %), but the crude protein content and amino acid profile of the two groups were similar. Catfish are traditionally grown in earthen ponds under semi-intensive conditions in southern Africa, at around 4 kg of fish per cubic meter of water (kg.m⁻³). However, the hybrid could tolerate densities of up to 415 kg of fish per cubic metre of water, if the water was exchanged hourly (kg.m⁻³.hr⁻¹), and the density at which yield was optimised was rounded off to 400 kg.m³.hr⁻¹. The high threshold density and water quality tolerances of the H. longifilis ♂ x C. gariepinus ♀ hybrid indicates that it is ideally suited for highly intensive aquaculture. It was concluded that it would be more productive to farm the HL♂xCG♀ hybrid on an intensive basis in southern Africa, than it would be to farm C. gariepinus in the traditional manner.
  • Full Text:
  • Date Issued: 1996

Project water (Grahamstown) : a case study of the development of an environmental education project

Aspects of the anaerobic digestion of wattle tannins

  • Authors: Hurlow, Elton Lloyd
  • Date: 1987
  • Subjects: Tanneries -- Waste disposal
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:4300 , http://hdl.handle.net/10962/d1004909
  • Description: The aqueous extract from the bark of the black wattle tree, (Acacia mearnsii De Wild)(1), is used extensively in the tanning industry for the production of sole and other heavy leathers as well as in lighter leathers and skins. The commercial extract is available in an easily dissolvable spray dried form and in deference to its genus name Mimosaceae is referred to in the trade as Mimosa(3). Mimosa extract consists primarily of high molecular weight polymeric flavonoid units which also constitutes the active tanning ingredient. Lower phenolics, gums and sugars or the so called "non-tannins" are present as impurities and contribute up to 40% to (3 ) the total mass of the extract.
  • Full Text:
  • Date Issued: 1987

A study of the ecology, behaviour and systematics of Tockus Hornbills

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