The impact of labour legislation on selected small firms in Mbombela (Nelspruit)
- Authors: Dlamini, Sikhulile Blessing
- Date: 2021
- Subjects: Labor laws and legislation -- South Africa , Small business -- Law and legislation-- South Afric , Small business -- South Africa -- Mbombela -- Case studies
- Language: English
- Type: text , Thesis , Masters , MSocSci
- Identifier: http://hdl.handle.net/10962/170781 , vital:41959
- Description: This study uses the theoretical framework of industrial relations pluralism, to study and analyse the impacts of labour legislation on six small firms (employing less than 50 workers) based in Mbombela (formerly Nelspruit), Mpumalanga province, South Africa. The analysis is based on the viewpoints of six managers and how they see the impacts of labour legislation on their respective firms. The analysis is aided by utilising theory and literature to make sense of the manager perspectives on the topic. Also, utilising a qualitative research design to collect and analyse the data, the study presents diverse findings in terms of how the participants perceived and experienced certain types of legislation. Some managers believed that the benefits of labour legislation outweighed the costs. While others believed the exact opposite. At an overall level, the study revealed that most of the participants were not as severely affected by labour legislation as might be expected; given the scarcity of resources in most small firms. This was partly because of various coping strategies and practices (mostly involving the use of informal procedures) that were adopted by the firms. Also, some small firms who aimed at expanding their businesses strategised to adopt some formal procedures and practices in order to easily absorb labour legislation and subsequently mordenise their businesses in the process. While a few firms persisted with more informal customs as they appeared cost-effective and necessary in their particular market positioning.
- Full Text:
- Date Issued: 2021
Nutrient removal and biofuel potential of MaB-floc biomass from an integrated algal pond system treating domestic sewage
- Authors: Sibelo, Linda
- Date: 2020
- Subjects: Biomass energy , Waste products as fuel , Algal biofuels , Sewage -- Purification -- Nutrient removal
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/144955 , vital:38395
- Description: Integrated algal pond systems (IAPS) are a passive water treatment technology derived from the Oswald designed advanced integrated wastewater pond systems (AIWPS®) and effect wastewater treatment based on biological activity of microorganisms within the system, solar energy and gravity. The technology consists of an advanced facultative pond (AFP), a series of interconnected high rate algal oxidation ponds (HRAOP) and algal settling ponds. The symbiotic relationship between microalgae and bacteria facilitated by paddlewheel mixing of HRAOP results in the formation of biomass aggregates known as MaB-flocs. MaB-floc formation enhances nutrient abstraction, gravitational sedimentation and separation from water hence forming two product streams; recyclable water and biomass, both with valorisation potential. This work aimed to determine the suitability of MaB-floc biomass generated in the HRAOP of an IAPS treating domestic sewage as feedstock for biofuel production based on the content of carbohydrate and lipid. Nutrient removal efficiency, biomass productivity and bulk lipid and carbohydrate concentration were monitored for two consecutive three-month periods in the winter and summer seasons of 2018/19. Maximum removal efficiencies of nitrogen and phosphorus were determined as 71% and 75% respectively, demonstrating the efficiency of IAPS as a wastewater treatment technology. MaB-floc biomass productivity in winter and summer was 9.4 g/m2/d and 16.5 g/m2/d respectively indicating the heavy influence of seasonal temperature, possibly day length, and solar irradiation on biomass productivity in the HRAOP. Summer productivity was lower than the maximum theoretical productivity of 25 g/m2/d possibly due to photoinhibition of photosynthesis as well as grazing pressures caused by the proliferation of rotifers mainly of the Brachionus genus. MaB-floc biomass consistently contained higher amounts of carbohydrate than lipid despite the changes in species dominance from Scenedesmus sp. and Desmodesmus sp. in winter to Pediastrum sp. in summer. Variations in MaB-floc biomass carbohydrate content were linked to changes in nitrogen concentration, mainly in the form of nitrates. Lower nitrogen concentration significantly increased the carbohydrate content of MaB-floc biomass from 17.5 ± 0.15% to 33.5 ± 0.3 % recorded in summer. In winter, biomass carbohydrate increased from 18.3 ± 1.2% to 35.8 ± 0.3%.To induce accumulation of carbohydrates through nitrogen starvation, isolated microalgal species native to the HRAOPs of the IAPS at Institute for Environmental Biotechnology Rhodes University(EBRU) were used. The outcome from the laboratory studies showed that carbon partitioning within isolated strains could be altered from carbohydrate to lipid which is more energy-rich. Hence, exploring the biodiesel production option using HRAOP MaB-floc biomass, which had a lipid content ranging between 12.1 ± 0.64 % and 13.9 ± 0.5 %, would require a preconditioning step in the form of nitrogen starvation to enhance its lipid content. Overall, the outcome of outdoor monitoring studies on biomass biochemical composition indicated that HRAOPs operating under natural environmental conditions preferentially generated a biomass rich in carbohydrate. Therefore, anaerobic digestion may be a more viable option for HRAOP MaB-floc biomass because of the high carbohydrate levels ranging between 24.9 ± 0.6 % and 25.6 ± 1.3 % of the dry MaB-floc biomass weight. Despite the low biomass C/N ratio (7.1 to 7.8), the MaB-floc biomass can be anaerobically co-digested with a higher C/N ratio (24) substrate such as in-pond digester sludge, to improve methane yields calculated to be between 0.31 m3 CH4/ kg MaB-floc biomass and 0.33 m3 CH4/ kg MaB-floc biomass. Anaerobic digestion of biomass also produces CO2 which can be recovered and added to HRAOPs to enhance MaB-floc biomass productivity while lowering greenhouse gas emissions from a wastewater treatment plant. The digestate from the anaerobic process, which is rich in nitrogen and phosphorus can be used as a biofertiliser. Thus, a potential MaB-floc biomass biorefinery consisting of biogas and bio-fertiliser pathways can be established using IAPS treating sewage as the platform technology. IAPS is a system designed to operate in a way that is passive and without substantial environmental impact but technological innovations and a reduction in the size of the system are required to make the technology more acceptable.
- Full Text:
- Date Issued: 2020
Research & innovation report 2018/19
- Date: 2019-10
- Subjects: Nelson Mandela University , Universities and colleges -- Research
- Language: English
- Type: text , book
- Identifier: http://hdl.handle.net/10948/39928 , vital:35546
- Description: Annual report highlighting the research and innovation undertaken by the Nelson Mandela University
- Full Text:
- Date Issued: 2019-10
Investigating thermal physiology as a tool to improve the release efficacy of insect biological control agents
- Authors: Griffith, Tamzin Camilla
- Date: 2018
- Subjects: Aquatic weeds -- Biological control , Water hyacinth -- Biological control , Insects -- Physiology , Miridae -- Effect of low temperatures on , Cold adaptation , Insects as biological pest control agents , Eccritotarsus catarinensis
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/63301 , vital:28391
- Description: Biological control is commonly used for the control of invasive aquatic weeds, which often involves the release of multiple host-specific agents. Releasing multiple agents has inherent safety concerns as the introduction of each new agent is associated with risks, but is often required to improve control where establishment is limited. Climatic incompatibility between the agent’s thermal physiology and its introduced range often causes agents to fail to establish. However, it has been suggested that the thermal physiology of insects is plastic. Therefore, the potential to manipulate their thermal physiologies before releasing them into the field needs to be explored; reducing the need to release additional agents, thereby ensuring the safety of biological control. This thesis therefore aimed to firstly, determine whether season and locality influenced the thermal physiology of two field populations of a water hyacinth (Eichhornia crassipes) control agent, the mirid Eccritotarsus catarinensis; one collected from the hottest establishment site, and one collected from the coldest establishment site in South Africa. Their thermal physiology was significantly influenced by season and not by the sites’ climate, suggesting their thermal physiology is plastic under field conditions. Secondly, the classical method of determining the lower critical thermal limit (CTmin), and a new respirometry method of determining this limit, compared the thermal physiology of two Eccritotarsus species reared in quarantine. Eccritotarsus catarinensis was significantly more cold tolerant than the more recently released Eccritotarsus eichhorniae, despite similar maintenance conditions, and as such, was used to establish whether cold hardening under laboratory conditions was possible. Successfully cold hardened E. catarinensis had a significantly lower CTmin compared to the field cold acclimated population, suggesting that cold hardening of agents could be conducted before release to improve their cold tolerance and increase their chances of establishment, allowing for further adaptation to colder climates in the field to occur. Increasing establishment of the most effective agents will decrease the number of agents needed in a biological control programme, thus encouraging a more parsimonious approach to biological control.
- Full Text:
- Date Issued: 2018
Exploring rural parents’ attitudes and experiences towards teaching and learning of the topics of human reproduction in junior secondary schools: a Namibian case study
- Authors: Kavila, Kornelius Embumbulu
- Date: 2017
- Subjects: Human reproduction -- Study and teaching (Secondary) -- Namibia , Parents -- Namibia -- Attitudes , Sex instruction for teenagers -- Namibia , Sexual health -- Study and teaching -- Namibia
- Language: English
- Type: Thesis , Masters , MEd
- Identifier: http://hdl.handle.net/10962/13543 , vital:21836
- Description: The Namibian school curriculum mandates that the subject of Life Science should be taught in all schools from grade 8-10. Among the main themes in this subject is Human Biology which covers topics of human reproduction. According to the Junior Secondary Certificate JSC Life Science Examiners’ reports (2010-2015), and my personal experience, learners perform poorly in the topics of human reproduction. Many of the parents in Namibian communities are not comfortable talking to their children about their sexuality, and some believe that communication about sexuality could influence adolescents to become more sexually active (Silas, 2015). Yet, there is agreement among educationists that parents’ involvement in their children’s education has an impact on the mediation of concepts, skills and attitudes. It is against this backdrop that this study explored rural parents’ attitudes and experiences towards teaching and learning of the topics of human reproduction being taught to their children in junior secondary schools (Grade 8-10). This study was informed by Vygotsky’s socio-cultural theory with the focus on how adults and peers influence individual learning and how cultural beliefs impact on instruction and learning in science classrooms. The sociocultural theory was supplemented by the Feminist Standpoint Theory (FST) with the focus on how different knowledge systems and standpoints produced from a specific social community (that is, rural parents) in terms of who to say what and when, to whom regarding sex-related information. The study was located within the interpretive paradigm. Within an interpretive paradigm, a case study approach was employed. This case study used a mixed method approach, that is, both quantitative and qualitative data were gathered to help understand the subjective nature of human’s attitudes and experiences. Data were collected using an administered questionnaire with twenty-two rural parents, workshop observation and semi-structured interviews with four of the twenty-two participated parents. Additionally, data from documents such as textbooks and curriculum documents were used to strengthen the context of this study. The study provided valuable information regarding issues around discussions about sex education. It revealed that the majority of rural parents regard sexual health education a taboo. However, the majority are of the supportive attitude towards sexual health education. The study provided some insights on the factors that influence rural parents’ attitude and experiences towards sexual health education. It was also found that parent-child communication is an essential skill, which needs to be developed either through parents’ workshops or other means to support and empower parents to understand the importance of teaching and learning about sexual health issues. It is also recommended to empower and support parents on how to talk to their children about sexual health issues.
- Full Text:
- Date Issued: 2017
An analysis of the Libor and Swap market models for pricing interest-rate derivatives
- Authors: Mutengwa, Tafadzwa Isaac
- Date: 2012
- Subjects: LIBOR market model , Monte Carlo method , Interest rates -- Mathematical models , Derivative securities
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5573 , http://hdl.handle.net/10962/d1005535
- Description: This thesis focuses on the non-arbitrage (fair) pricing of interest rate derivatives, in particular caplets and swaptions using the LIBOR market model (LMM) developed by Brace, Gatarek, and Musiela (1997) and Swap market model (SMM) developed Jamshidan (1997), respectively. Today, in most financial markets, interest rate derivatives are priced using the renowned Black-Scholes formula developed by Black and Scholes (1973). We present new pricing models for caplets and swaptions, which can be implemented in the financial market other than the Black-Scholes model. We theoretically construct these "new market models" and then test their practical aspects. We show that the dynamics of the LMM imply a pricing formula for caplets that has the same structure as the Black-Scholes pricing formula for a caplet that is used by market practitioners. For the SMM we also theoretically construct an arbitrage-free interest rate model that implies a pricing formula for swaptions that has the same structure as the Black-Scholes pricing formula for swaptions. We empirically compare the pricing performance of the LMM against the Black-Scholes for pricing caplets using Monte Carlo methods.
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- Date Issued: 2012
An analysis of the influence of domestic macroeconomic variables on the performance of the South African stock market sectoral indices
- Authors: Hancocks, Ryan Lee
- Date: 2011
- Subjects: Johannesburg Stock Exchange , Stock price indexes -- South Africa , Interest rates -- South Africa , Macroeconomics -- Econometric models
- Language: English
- Type: text , Thesis , Masters , MCom
- Identifier: vital:954
- Description: An econometric study was undertaken to determine the extent to which selected macroeconomic variables influenced stock market prices on the All-Share, Financial, Mining and Retail Indices of the Johannesburg Stock Exchange in South Africa from 1996:7 to 2008:12. The Johansen cointegration method was used to determine whether cointegrating relationships existed between the macroeconomic variables and the stock market indices. A Vector Error Correction model was estimated and found significant results that money supply, inflation, long and short- run interest rates, and the exchange rate all had an influence on stock market prices. Further, the VECM results for each sector indicated that certain macroeconomic variables had differing influences on each sector of the stock market. Impulse Response tests indicated that the selected macroeconomic variables caused shock to the sectoral indices in the short-run but that the effect was lagged. The Variance Decomposition tests conducted supported earlier evidence that the macroeconomic variables had a strong level of sectoral index determinacy in the long run. The results found that the All-Share and Financial Indices were negatively influenced by inflation and short term interest rates in the long run, while the Financial Index also had a negative relationship with long-run interest rates. Money supply was found to have a positive effect on all the indices. A weakening of the exchange rate was found to have a positive influence on both the Retail and Mining Indices, while it negatively affected the All-Share and Financial Indices. The long-run interest rate had a positive influence on both the Retail and Mining Indices. Overall the study finds that macroeconomic variables are important determinants of stock market prices in South Africa and that it is important to examine each sector of the stock market separately to capture what are different effects. The limitations of the study are that a different measure for exchange rates from the nominal rand/dollar exchange rate used here may yield more decisive results and provide insight into the link between exchange rate behaviour and performance of especially the retail sector.
- Full Text:
- Date Issued: 2011
Tributes to Comrade Richard Owen Dudley
- Date: 2009
- Subjects: South Africa -- Politics and government , Government, Resistance to -- South Africa
- Language: English
- Type: text , book
- Identifier: http://hdl.handle.net/10948/36936 , vital:34067 , Bulk File 7
- Description: This is one of many individual publications put out by the New Unity Movement and consists of a number of tributes to Richard Owen Dudley.
- Full Text: false
- Date Issued: 2009
Investigating a rural community's use of communication technology: a study of Nakaseke Community Multi-media centre in Uganda
- Authors: Tumusiime, James
- Date: 2006
- Subjects: Information technology -- Uganda , Media programs (Education) -- Uganda , Communication in rural development -- Uganda , Communication -- Technological innovations -- Developing countries , Telecommuting centres -- Uganda
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:3489 , http://hdl.handle.net/10962/d1002944 , Information technology -- Uganda , Media programs (Education) -- Uganda , Communication in rural development -- Uganda , Communication -- Technological innovations -- Developing countries , Telecommuting centres -- Uganda
- Description: An assumption that Information and Communication Technologies (ICTs) and economic development have an automatic linkage has gained wide acceptance over the last decade. As a result, developing countries are under pressure to apply this prescription as a solution to poverty. With the help of development partners in the developed world and the United Nations, developing countries have embraced this call to increase access to ICTs to bridge the ever-widening gap between the ‘information rich’ and ‘information poor’ (Castells, 2001). One of the strategies has been the establishment of telecentres where the least privileged people might access ICTs for their own development needs. However, this strategy has tended to overlook contextual factors and circumstances in developing countries. ICTs are thus being introduced in an environment of mass poverty, illiteracy and poor infrastructure, exacerbating existing inequalities in some cases. Much attention has been focussed on initiatives aimed at expanding the ICT infrastructure for wider population access without addressing what the users actually do with such access. This study aims to make a contribution in that direction. The study focuses on Nakaseke Community Multi-media Centre(CMC), the first telecentre introduced in Uganda in 1997. Using a combination of quantitative and qualitative research techniques, the study sets out to develop deeper insights into how the Nakaseke community uses, engages with and relates with communication technologies installed at the telecentre. It probes whether these practices advance the dominant view that ICTs are a panacea for rural development. The findings indicate that while access to communication technology has expanded, albeit at a slow pace, the benefits might take very long to have a significant effect as many targeted users do not make use of the facilities because they lack the human skills and financial resources to exploit the technologies. Other problems such as poor electricity supply and sustainability also actively militate against the potential of the project to deliver. Besides, people tend to appropriate technology in ways different from those intended by its promoters. As Burton (2002) explains through the concept of ‘affordances’ and ‘culture’, some users perceive technologies essentially as something that bestows the status of being modern or sophisticated on their community, rather than as a development tool. In conclusion, it is argued that if used for development, ICTs can indeed make a difference in the lives of rural people. However, besides investing in technology, there is need to invest more in empowering the people themselves with skills, particularly literacy, to enable them use ICTs productively.
- Full Text:
- Date Issued: 2006
Processes that influence the experiences of children living with mothers that have HIV: two case studies
- Authors: Castelletto, Simona
- Date: 2004
- Subjects: AIDS (Disease) in women , AIDS (Disease) -- Social aspects -- South Africa , HIV infections -- Social aspects -- South Africa , Mothers and daughters -- Social aspects , Mothers and sons -- Social aspects , AIDS (Disease) in children -- Social aspects -- South Africa
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:3166 , http://hdl.handle.net/10962/d1007728 , AIDS (Disease) in women , AIDS (Disease) -- Social aspects -- South Africa , HIV infections -- Social aspects -- South Africa , Mothers and daughters -- Social aspects , Mothers and sons -- Social aspects , AIDS (Disease) in children -- Social aspects -- South Africa
- Description: Maternal HIV-infection is considered to be a threat to the psychosocial development of AIDS-affected children. In South Africa, AIDS-affected children may be particularly vulnerable due to the unprecedented effects of the HIV/AIDS epidemic on the breakdown of family and community resources in already disadvantaged communities. The aim of this study was to explore the contextualised experiences of two children living with mothers who have HIV by conducting two case studies. Mother-child dyads were recruited from local HIV/AIDS centres and informed consent was obtained. The mothers were in the minor symptomatic phase of HIV-infection and the children were uninfected and aged between 10 and 12 years. Through semi-structured interviewing, the mothers provided background and contextual information about the children. Play techniques were used in the child interviews to encourage the introduction and exploration of issues salient to the children. Play facilitated engagement around sensitive and potentially anxiety-provoking material. A key issue for the children was their concerns about the anticipated deaths of their mothers. The children held misconceptions about the transmission of HIV/ AIDS. They feared HIV/AIDS and expected that others would have negative perceptions of them. Family processes such as secrecy and avoidance around HIV/AIDS-related issues were understood to perpetuate the children's fears and false beliefs in a broader community context that stigmatised HIV/AIDS. It was argued that the mothers' shame over HIV-infection and their need to protect their relationship with their children compromised their ability to communicate openly with their children and to offer them meaningful emotional support. Limited parental involvement was identified as the key contextual process that engendered vulnerability in the children, as they were isolated within and beyond the family. Recommendations to address the processes that engendered vulnerability in the children are discussed.
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- Date Issued: 2004
Rural students' local knowledge of learning in formal and informal contexts
- Authors: Visser, Alvin-Jon
- Date: 2000
- Subjects: Non-formal education -- South Africa , Education and state -- South Africa , Rural children -- Education -- South Africa , Black people -- Education -- South Africa , Community and school -- South Africa , Education, Rural -- Social Aspects -- South Africa , Rural schools -- South Africa
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:3079 , http://hdl.handle.net/10962/d1002588 , Non-formal education -- South Africa , Education and state -- South Africa , Rural children -- Education -- South Africa , Black people -- Education -- South Africa , Community and school -- South Africa , Education, Rural -- Social Aspects -- South Africa , Rural schools -- South Africa
- Description: The general aim of this thesis is to illuminate the process of learning as it occurs in formal and informal contexts. The study focuses on South African scholars attending school in rural areas where the contrast between learning in formal and informal learning contexts is more pronounced than that in urban areas. The research draws on rural scholars' local knowledge of formal and informal learning contexts in order to gain a rich insight into how cognition is situated in different learning contexts. This is accomplished through investigating the structure of the respective learning tasks, the mediators involved, the task objectives and the means for achieving these objectives in the different learning contexts. The thesis draws on a socio-cultural approach to the study of cognitive development to probe the activity of learning in a formal and informal learning context. Through the use of a context sensitive methodological methods especially Participatory Rural Appraisal (PRA) tools and techniques, it was possible to illuminate tacit local knowledge structures and to get participants to actively explicate their understandings related to learning in different contexts The research results illustrate the assertion that the activity of learning is fundamentally situated in the learning context from which it arises. Learning is framed by the community of practice which structures affordances for situated learning, through mediation, within zones of proximal development. Learning in a formal context such as the school is often abstract, rule-based, standardised and theory related. Learners also find it difficult to reflect on the learning tasks and the mediational means used in a formal learning context. In contrast, the learning which takes place in an informal setting is often practical, individualised, flexible and environment based. This learning is structured around everyday activities and is dynamically defined and supported. In a situation where a learner is exposed to dislocated learning contexts, the essential goal of educational initiatives is to bridge the gap between the two. This can be achieved through mediators creating effective zones of proximal development which facilitate the individuals adaptation between learning contexts. Exposing rural scholars' local knowledge of learning in formal and informal contexts allows for a fuller understanding of the cognitive development structured within formal and informal communities of practice. It is this understanding that is necessary to address the situation where learning contexts, drawing on different knowledge bases find ways of thinking, prove challenging and/or conflicting to the scholar.
- Full Text:
- Date Issued: 2000
The manufacture of chaos and compromise: an analysis of the path to reform in South Africa
- Authors: Ryklief, Cheryl Cecelia
- Date: 1996
- Subjects: South Africa -- Politics and government -- 1994- , Apartheid -- South Africa -- History , South Africa -- Race relations , Black people -- South Africa -- Politics and government , South Africa -- Social conditions
- Language: English
- Type: text , thesis
- Identifier: http://hdl.handle.net/10962/76218 , vital:30521
- Description: This dissertation examines the factors leading to the opening of negotiations to majority rule in South Africa. It argues that changes to the socio-economic environment led to the growth of the strategic relevance of the black working class, and also created certain points of collision between the black working class and the policies of the state. These sectoral collisions engendered both the partial reforms of the Botha era as well as the rejection of these reforms by the black majority. The developments that emerged from the ensuing process of reform, resistance and repression in the 1980s weakened both the state and the black opposition sufficiently to allow for the emergence of a consensual solution to the political stalemate. , Dissertation submitted in accordance with the requirements of the University of Liverpool for the degree of Master of Arts
- Full Text:
- Date Issued: 1996
Chemical Workers Industrial Union: Shop steward foundation course
- Authors: Chemical Workers Industrial Union
- Date: 199u
- Subjects: Uncatalogued
- Language: English
- Type: book , text
- Identifier: http://hdl.handle.net/10962/68700 , vital:29306
- Description: This document is the shop steward foundation course manual.
- Full Text:
- Date Issued: 199u
The culture of Penaeus Indicus Milne Edwards in experimental closed systems with special reference to water quality
- Authors: Gerhardt, Hedley Vernon
- Date: 1979
- Subjects: Penaeus Indicus , Aquatic animals , Water quality
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5595 , http://hdl.handle.net/10962/d1002045 , Penaeus Indicus , Aquatic animals , Water quality
- Description: This study embraces two aspects of closed system culture: (a) a comparative study of four different biological filtration treatments, and (b) a quantitative determination of the nitrogen flow in a particular biological filtration system. Twenty 0,5 g juvenile Penaeus indicus Milne Edwards were cultured for approximately two months in four different kinds of sea water recirculatory systems with bacterial filtration, algal filtration, algar plus bacterial filtration and water exchange (25% every 3 days). Growth was comparable to that found in the literature for P. indicus. Nitrification occurred in all systems irrespective of the type of biological filtration employed. Ammonia, nitrite and nitrate levels were reduced by the algae, but nitrate accumulated to approximately 30 mg NO¯³ -Nℓ¯¹ in those systems without algae. Depletion of trace elements (Cu, Fe, Zn, Hn and Co) by the algae did not occur due to trace metal replenishment from the addition of food. No marked changes occurred in the concentrations of the major cations (Ca⁺⁺, Mg⁺⁺, Na⁺ and K⁺), but a small increase in Ca⁺⁺ levels was detectable in those systems with oyster shell chips in the filtration medium. Only minor changes occurred in oxygen or pH values in the various systems tested. Inorganic carbon levels showed major increases in the algal filtration systems, while a slight drop occurred in the bacterial filtration systems. The increase in the algal filtration systems was thought to be due to the formation of carbonates and bicarbonates by the reaction of respiratory CO₂ with unionized ammonia and water. Suggestions are made as to how closed systems can be improved upon. By determining the rate of excretion of P.indicus as related to size and temperature, its faecal production, and the nitrogen content of P.indicus, its food and faeces, the nitrogen flow within a system could be calculated. P.indicus was found to have an assimilation efficiency of 88,93% and a food conversion ratio of 3,49:1. Of the total dietary nitrogen input into the system, P.indicus ingested 69,02% - 19,80% of which was used for growth, 41,58% excreted and 7,64% lost as faeces. The remaining 30,98% of the total nitrogen input can be regarded as excess food nitrogen. The total nitrogen loading on the biological filtration system was found to be 80,20% of the total input of dietary nitrogen. The ability of various types of filamentous algae to remove these nitrogen compounds was determined. Suggestions are made as to the application of this information on nitrogen flow to the culture of P.indicus
- Full Text:
- Date Issued: 1979