The Nile perch, Lates niloticus (Linnaeus, 1758), is a predacious freshwater fish widely distributed throughout the Afro-tropic eco-zone. The species was introduced to Lake Victoria in the early 1950s and by 1980 it had dominated the fisheries of Lake Victoria. This was followed by a dramatic decrease in the Nile perch fisheries production due to uncontrolled exploitation. The purpose of this thesis is to provide fundamental knowledge that can be applied in aquaculture and fisheries management through the study of the reproductive biology of L. niloticus. The research was aimed at the studying of the diverse aspects of the reproductive biology of L. niloticus in the Lake Victoria, Ugandan populations. This included reproductive patterns in relation to proximate environmental conditions, size at sexual maturity, gonad and gamete structure, gametogenesis and induced ovulation. The size at 50% sexual maturity for female Nile perch was 59.4 cm, which is lower than the earlier reported size of greater than 90 cm total length. Male L. niloticus matured at 57.8 cm total length in Lake Victoria. Microscopy revealed that L. niloticus from Lake Victoria had one spawning period that started in November and ended in March. Type I atresia occurred at high frequency from March to June, and type III atresia was present from July to September and between November and December. Spermatogenesis in L. niloticus is cystic and sperm development is the result of asynchronous activation of the germ cells. Type II spermatozoa are simple, uni-flagellate aquasperm with no acrosome. Oogenesis in L. niloticus differed from that of other fishes in that no cortical alveoli were present in any stage of oogenesis. Numerous oil globules were present in the primary yolk vesicle stage. This formed one centrally positioned, large oil globule in the tertiary yolk vesicle oocytes during final oocyte maturation. Clove oil was an effective sedative and an anaesthetic for the handling of L. niloticus. Induction time was more rapid at clove oil concentrations of 50 - 100 μl L⁻¹ than in fish exposed to clove oil concentrations less than 50 μl L⁻¹. Fish exposed to high concentrations exhibited significantly short induction times of less than 240 seconds. On average, fish recovered within 673 ± 58 seconds for all the concentrations used. Prolonged exposure of L. niloticus to low clove oil concentrations of 2.5 - 10 μl L⁻¹ did not change the blood plasma cortisol, glucose, and the lactate and chloride ion concentration, relative to the control treatment. Captive breeding was attempted by conducting induced spawning experiments. Only final oocyte maturation was achieved using a decapeptide Gonadotropin Releasing Hormone (Dargin, sGnRH-MET), combined with a water-soluble dopamine receptor antagonist metoclopramide. This thesis suggests a research approach that provides a basis for aquaculture of the new species by first studying reproductive biology patterns and then linking the information to gonad and gamete structure so that spawning times can be estimated. It further provides insights into aspects of the reproductive biology of the species and the effects of hormonal intervention on oocytes by showing at which stage of oocyte development hormones should be applied in L. niloticus. Clove oil can be used to sedate and anaesthetise L. niloticus broodfish to reduce the stress related to the handling of large specimens.

Thesis (MScAgric (Conservation Ecology and Entomology)--University of Stellenbosch, 2007. / Small farm dams (< 20 ha) in the Western Cape Province provide adequate water conditions for intensive cage production of rainbow trout (Oncorhynchus mykiss). A major environmental concern of cage aquaculture, however, is the high inputs of nutrients via commercial diets and the subsequent eutrophication of the water source. Eutrophication can result in the degradation of the general water quality (increasing pH levels, oxygen depletion, increased hydrogen sulphide and free ammonia) and shifts in the phytoplankton structure (increased biomass, single species dominance). Deterioration of water quality will affect the success of the fish farming enterprise as well as the performance of irrigation equipment by increasing the risk of clogging and corrosion. Water quality, phytoplankton and zooplankton compositions were monitored at four sites from June 2005 to November 2006 to determine the effects of cage culture on the farm dam environment, its associated biota as well as irrigation water quality. The distribution of nutrients, nitrogen and phosphorus, was mainly influenced by the stratification and mixing regime of the water bodies. Nutrient concentrations increased during the winter mixing period while in the summer months, they seem to settle to the lower part of the water column. Nutrient concentrations of production sites and reference sites were comparable except for the ammonia levels that were significantly higher at the production sites. Phytoplankton corresponded with nutrient availability resulting in high biomass during winter. In terms of biomass, phytoplankton was approximately two times more abundant in production sites compared to reference sites. Assemblage dominance by cyanophytes (Anabaena circinalis, Microcystis spp.) was found more often in production sites, while reference sites were dominated by dinophytes (Ceratium hirundinella, Peridinium spp.). Zooplankton biomass concurred with high phytoplankton biomass in winter. Zooplankton assemblages in production sites sustained much higher biomass. Effects of cage culture on irrigation water quality are evident from increased algal biomass and shifts in species composition. These results indicated that at its present production level, cage culture had impacts on the farm dam environment and irrigation water quality. The most significant evidence was given by increased plankton biomass and single species dominance in production sites. However, these findings can not solely be ascribed to the introduction of aquaculture as various other factors may also contribute to the water quality of these ecosystems.

Thesis (MPhil)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Stellenbosch University was approached to assist with developing a techno-financial model for an urban freshwater aquaculture system in Philippi, Cape Town. Rapidly growing urban areas are predominantly becoming concentrated zones for malnutrition and poverty which require attention. Having enough food to eat does not mean that a family is food secure, the problem is usually associated with the lack of access to nutritious food. Fish is seen as an extremely healthy food which has the potential to effectively support food security and alleviate malnutrition. Aquaculture is identified as a largely underdeveloped sector in South Africa. It is currently undergoing rapid transition, being promoted by government as an industry that has potential to develop and create jobs, provide food security and grow the South African economy. Aquaponics- a method to integrate aquaculture with growing crops in a symbiotic system is a highly resource efficient closed-integrated food producing technology which has the potential to benefit from South African biosecurity regulations and climate-geographic characteristics. It is viewed as an effective food production alternative to deal with the challenges of declining high quality freshwater resources and available arable land. Training and capacity building is important for the development of aquaponic technology. This study explores and identifies the advantages aquaponic technology development would have in South Africa. The study has reviewed and assessed the fundamental principles for aquaculture production and management required for aquaponic systems development and management. A practical case study identifies the daily challenges and design parameters of aquaponic systems. The study is concluded with a techno-financial project proposal which shows how aquaponic systems can be planned. / AFRIKAANSE OPSOMMING: Universiteit Stellenbosch was genader om 'n tegno-finansiele model to ontwikkel vir 'n stedelike akwakultuur plaas in Philippi, Kaapstad. The tempo waarteen die stedelike areas groei ontwikkel kommerwekkende uitdagings soos wanvoeding en armoede. In hierdie studie is vis geindentifiseer as 'n uiters voedsame aanvulling in die dieet van Suid Afrikaners. Akwakultuur is grootliks agter in terme van ontwikkeling. Dit word beskou as 'n sektor wat groot potensiaal inhou vir Suid Afrika se eknomiese groei, werkskepping en voedselsekuriteit. Akwaponika is die hersirkulerende integrasie van akwakultuur en hidroponika. Akwaponika hou groot voordele in terme van Suid Afrika se biosekuriteit regulasies and geografiese eienskappe en is 'n effektiewe manier om gebruikte akwakultuur te suiwer. Opleiding en beplanning word gesien as 'n fundamentele benadering tot suskesvolle akwaponika ontwikkeling. Hierdie studie bestudeer die Suid Afrikaanse omgewing en potensiaal vir akwaponika ontwikkeling. Die fundamentele beginsels van akwakultuur en hidroponika bestuur en produksie is saamgesit wat beskou word as die aanbevele manier om akwaponika te bestuur. 'n Praktiese gevallestudie toon die daaglikse uitdagings aan en gee raad oor daaglikse bestuur van akwaponika stelsels. Die studie word afgesluit met 'n tegno-finansiele model wat wys hoe om 'n akwaponika sisteem te beplan.

Cette thèse comporte trois essais en économie des ressources naturelles. Le Chapitre 2 analyse les effets du stockage d’une ressource naturelle sur le bien-être et sur le stock de celle-ci, dans le contexte de la rizipisciculture. La rizipisciculture consiste à élever des poissons dans une rizière en même temps que la culture du riz. Je développe un modèle d’équilibre général, qui contient trois composantes principales : une ressource renouvelable à accès libre, deux secteurs de production et le stockage du bien produit à partir de la ressource. Les consommateurs stockent la ressource lorsqu’ils spéculent que le prix de cette ressource sera plus élevé dans le futur. Le stockage a un effet ambigu sur le bien-être, négatif sur le stock de ressource au moment où le stockage a lieu et positive sur le stock de ressource dans le futur. Le Chapitre 3 étudie les effects de la migration de travailleurs qualifiés dans un modèle de commerce international lorsqu’il y a présence de pollution. Je développe un modèle de commerce à deux secteurs dans lequel j’introduis les questions de pollution et de migration dans l’objectif de montrer que le commerce interrégional peut affecter le niveau de pollution dans un pays composé de régions qui ont des structures industrielles différentes. La mobilité des travailleurs amplifie les effets du commerce sur le capital environnemental. Le capital environnemental de la région qui a la technologie la moins (plus) polluante est positivement (négativement) affecté par le commerce. De plus, je montre que le commerce interrégional est toujours bénéfique pour la région avec la technologie la moins polluante, ce qui n’est pas toujours le cas pour la région qui a la technologie la plus polluante. Finalement, le Chapitre 4 est coécrit avec Yves Richelle. Dans ce chapitre, nous étudions l’allocation efficace de l’eau d’un lac entre différents utilisateurs. Nous considérons dans le modèle deux types d’irréversibilités : l’irréversibilité d’un investissement qui crée un dommage à l’écosystème et l’irréversibilité dans l’allocation des droits d’usage de l’eau qui provient de la loi sur l’eau (irréversibilité légale). Nous déterminons d’abord la valeur de l’eau pour chacun des utilisateurs. Par la suite, nous caractérisons l’allocation optimale de l’eau entre les utilisateurs. Nous montrons que l’irréversibilité légale entraîne qu’il est parfois optimal de réduire la quantité d’eau allouée à la firme, même s’il n’y a pas de rivalité d’usage. De plus, nous montrons qu’il n’est pas toujours optimal de prévenir le dommage créé par un investissement. Dans l’ensemble, nous prouvons que les irréversibilités entraînent que l’égalité de la valeur entre les utilisateurs ne tient plus à l’allocation optimale. Nous montrons que lorsqu’il n’y a pas de rivalité d’usage, l’eau non utilisée ne doit pas être considérée comme une ressource sans limite qui doit être utilisée de n’importe quelle façon. / This thesis consists of three essays in resource economics. Chapter 2 analyzes the effects of resource storage on welfare and on the resource stock, in the context of rice-fish culture. I develop a simple general equilibrium model, that has three central components: one open access renewable resource with logistic natural growth, two production sectors and storage of the good produced with the resource. Consumers store the resource when they speculate that the price of the resource will be higher in the future. Storage has an ambiguous effect on welfare, has a negative impact on resource stock at the period the storage takes place and has a positive impact for all following periods. Chapter 3 examines the effects of migration of skilled workers in a model of interregional trade in the presence of pollution. I develop a two-sector model of trade that incorporates both pollution and migration issues to show that interregional trade can affect the pollution level of a country composed of regions with different industrial structures. The mobility of workers amplifies the effects of interregional trade on the environmental capital. The region with the less (more) polluting technology is affected positively (negatively) by trade. Migration doesn’t affect the trade pattern. The region with the less polluting manufacturing industry always gains from trade. If the preferences over manufactures is relatively low, the region with the more pollutant technology can experience a loss from trade in the long run. Finally, Chapter 4 is co-authored with Yves Richelle. In this chapter, we consider the problem of efficiently allocating water of a lake among different potential users. We consider two types of irreversibility: the irreversibility of an investment that creates a fixed damage to the ecosystem and the irreversibility of the right to use the resource that comes from the legislation (legislative irreversibility). First of all, we determine the value of water for users. Then, we characterize the optimal allocation of water among users. With legislative irreversibility, we show that it is sometimes optimal to reduce the amount of water allocated to the firm, even though there is no rivalry in use. Moreover, we show that it is not always optimal to prevent the damage created by the irreversible vi investment. We define the context, in which it is optimal to intervene to prevent the damage. Furthermore, with irreversibility, we prove that the marginal value of water at the efficient allocation for users is not equalized. Overall, we show that in the case of no rivalry in use, unused water should not be seen as a limitless resource to be used in any way whatever.

Doctorat en philosophie et lettres / info:eu-repo/semantics/nonPublished

The potential for aquaculture development to make up for an annual 400,000mt shortfall in domestic fish supply was investigated. This involved an overview of the sector to determine its trends and operations and identifying strengths and constraints, a financial viability assessment of the sector, based on mode and levels of operation of existing farms, an assessment of the market and trade for cultured fish with a focus on Oreochromis niloticus, and finally, a GIS approach to update and reassess the potential for aquaculture development in Ghana. Data were obtained from both primary and secondary sources, the former, via fish farmer, dealers and consumer questionnaire surveys. Results of the study showed that interests in fish farming continue to grow with an overall annual average growth rate of 16% since 2000. The existing farms, 1300 in number were however very small with a mean farm size of 0.36ha and a median 0.06ha of which commercial farms accounted for less than 3%. Based on sizes, mode of operation and levels of input and output, five subsistence farm types were identified. Mean production from these pond-based farms ranged from 1436kg/ha/yr- to 4,423kg/ha/yr while that of a medium sized intensive commercial pond farm was 45,999kg/ha/yr. Commercial farming accounted for about 75% of 2006 aquaculture production. The main strength identified was the growing interest in both commercial and non-commercial fish farming and the main constraints were lack of quality seed, low levels of technical support and of knowledge in fish farming practices among non-commercial farmers. Net profits of commercial farms ranged from GH¢ 3,341 (US$3480)/ha/yr to GH¢ 51,444 (US$ 53,587)/ha/yr with payback from 1 to 4yrs, IRR at 35% to 105% and NPV from GH¢ 5,898 to GH¢ 236,412. By contrast, only two of the five non-commercial farm types made positive net returns ranging, from GH¢158 to GH¢1100/ha/yr, with minimum payback period of 14yrs, NPVs of less than 1 and the best IRR being just 4%, when initial capital requirements are full costed. Uncosted family labour inputs and negligible land opportunity costs improved viabilities for two farm types, where net returns/ha/yr increased by more than 50%, minimum payback dropped to 2 years, NPV from GH¢ 4839 to GH¢ 9330 and minimum IRR of 45%. Main constraints identified as affecting the profitability of subsistence farming were the relatively low prices of fish and the low levels of output which could be improved through better farming practices. From the market survey, a huge market potential for tilapia was identified with a current supply deficit of 41,000mt. The most preferred sizes by consumers and with potentially good market price for traders were those weighing at least 200g. For dealers, trading in cultured fish was found to be more profitable than trading wild capture tilapia because of lower wholesaler prices, gross profit margins were GH¢ 0.49/kg and GH¢ 0.25/kg respectively. Preference for tilapia was influenced by taste, availability, and its perceived health benefit. A key constraint to the sector was poor post-harvest handling and preservation of the fish resulting in shorter shelf life. From the GIS study, 2% (3,692 km2) of available land area was identified as very suitable for subsistence and about 0.2% (313.8km2) for commercial farming. A further 97.4% and 84.0% were identified as suitable for subsistence and commercial farming respectively. Areas with potential for cage culture were also identified, which were largely in the southern and mid-sections of the country. The overall conclusions are that based on natural resource requirements, market potential and financial viability, Ghana has the potential to totally make up the shortfall in domestic fish supply through aquaculture production. The current 400,000mt shortfall in domestic fish production can be achieved by 2020 by increasing overall aquaculture production by 60% per annum.