List of Titles

Effect of adding a probiotic to an aquaponic system on plant and fish growth, water quality, and microbial diversity

Authors: Kasozi, Nasser
Date: 2022-04-08
Subjects: To be added
Language: English
Type: thesis , text , Doctoral , PhD
Identifier: http://hdl.handle.net/10962/294596 , vital:57236
Description: Thesis embargoed. Release date April 2023. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2022
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Date Issued: 2022-04-08

Movement patterns, stock delineation and conservation of an overexploited fishery species, Lithognathus Lithognathus (Pisces: Sparidae)

Authors: Bennett, Rhett Hamilton
Date: 2012
Subjects: Reef fishes -- Behavior , Endangered species -- South Africa , Fish stock assessment -- South Africa , Fishery management -- South Africa , Fish communities -- South Africa , Sparidae , Lithognathus , Lithognathus -- Growth
Language: English
Type: Thesis , Doctoral , PhD
Identifier: vital:5374 , http://hdl.handle.net/10962/d1015709
Description: White steenbras Lithognathus lithognathus (Pisces: Sparidae) has been a major target species of numerous fisheries in South Africa, since the late 19th century. Historically, it contributed substantially to annual catches in commercial net fisheries, and became dominant in recreational shore catches in the latter half of the 20th century. However, overexploitation in both sectors resulted in severe declines in abundance. The ultimate collapse of the stock by the end of the last century, and the failure of traditional management measures to protect the species indicate that a new management approach for this species is necessary. The species was identified as a priority for research, management and conservation in a National Linefish Status Report. Despite knowledge on aspects of its biology and life history, little is known about juvenile habitat use patterns, home range dynamics and movement behaviour in estuaries. Similarly, the movement and migration of larger juveniles and adults in the marine environment are poorly understood. Furthermore, there is a complete lack of information on its genetic stock structure. Such information is essential for effective management of a fishery species. This thesis aimed to address the gaps in the understanding of white steenbras movement patterns and genetic stock structure, and provide an assessment of its current conservation status. The study adopted a multidisciplinary approach, incorporating a range of methods and drawing on available information, including published literature, unpublished reports and data from long-term monitoring programmes. Acoustic telemetry, conducted in a range of estuaries, showed high site fidelity, restricted area use, small home ranges relative to the size of the estuary, and a high level of residency within estuaries at the early juvenile life stage. Behaviour within estuaries was dominated by station-keeping, superimposed by a strong diel behaviour, presumably based on feeding and/or predator avoidance, with individuals entering the shallow littoral zone at night to feed, and seeking refuge in the deeper channel areas during the daytime. Conventional dart tagging and recapture data from four ongoing, long-term coastal fish tagging projects, spread throughout the distribution of this species, indicated high levels of residency in the surf zone at the late juvenile and sub-adult life stages. Consequently, juvenile and sub-adult white steenbras are vulnerable to localised depletion, although they can be effectively protected by suitably positioned estuarine protected areas (EPAs) and marine protected areas (MPAs), respectively. It has been hypothesized that adult white steenbras undertake large-scale coastal migrations between summer aggregation areas and winter spawning grounds. The scale of observed coastal movements was correlated with fish size (and age), with larger fish undertaking considerably longer-distance coastal movements than smaller individuals, supporting this hypothesis. Given the migratory behaviour of adults, and indications that limited spawning habitat exists, MPAs designed to protect white steenbras during the adult life stage should encompass all known spawning aggregation sites. The fishery is plagued by problems such as low compliance and low enforcement capacity, and alternative management measures, such as seasonal closure, need to be evaluated. Despite considerable conventional dart tagging effort around the coastline (5 782 fish tagged) with 292 recaptures there remains a lack of empirical evidence of fish migrating long distances (> 600 km) between aggregation and spawning areas. This uncertainty in the level of connectivity among coastal regions was addressed using mitochondrial DNA sequencing and genotyping of microsatellite repeat loci in the nuclear genome, which showed no evidence of major geographic barriers to gene flow in this species. Samples collected throughout the white steenbras core distribution showed high genetic diversity, low genetic differentiation and no evidence of isolation by distance or localised spawning. Although historically dominant in several fisheries, analysis of long-term commercial and recreational catch data for white steenbras indicated considerable declines and ultimately stock collapse. Improved catch-per-unit-effort in two large MPAs subsequent to closure confirmed that MPAs can be effective for the protection of white steenbras. However, the current MPA network encompasses a low proportion of sandy shoreline, for which white steenbras exhibits an affinity. Many MPAs do not prohibit recreational shore angling, which currently accounts for the greatest proportion of the total annual catch. Furthermore, EPAs within the juvenile distribution protect a negligible proportion of the total available surface area of estuaries – habitat on which white steenbras is wholly dependent. Despite some evidence of recent increases in abundance in estuaries and the surf zone in certain areas, white steenbras meets the criteria for “Endangered” on the IUCN Red List of Threatened Species, and for “Protected species” status on the National Environmental Management: Biodiversity Act of South Africa. The species requires improved management, with consideration for its life-history style, estuarine dependency, surf zone residency, predictable spawning migrations and its poor conservation status. The multidisciplinary approach provides valuable information towards an improved scientific basis for the management of white steenbras and a framework for research that can be adopted for other overexploited, estuarine-associated coastal fishery species.
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Date Issued: 2012

Early stage ichthyofauna from shallow water habitats of the Angola-Benguela frontal zone

Authors: Farthing, Matthew William
Date: 2017
Subjects: Fishes -- Larvae -- South Africa -- Atlantic coast , Fishes -- Larvae -- Angola -- Atlantic coast , Striped mullet -- Angola -- Atlantic coast
Language: English
Type: Thesis , Masters , MSc
Identifier: http://hdl.handle.net/10962/50442 , vital:25988
Description: Early stage fishes (larvae and early juveniles) were collected from an array of shallow water (±1.5m) habitats on the warm-temperate southern Angolan coastline between June 2014 and June 2015. This study, the first assessment of the early stages of coastal fishes in Angola, provides important new understanding of non-estuarine shallow water nursery habitat use by coastal fishes from the region. In total, 51 species from 18 teleost families were observed. The exposed surf zone was dominated by postflexion larvae, while the moderately exposed beach and sheltered bay were dominated by early juveniles. Both fish density and diversity peaked in the wet season (Feb – Apr 2015) for all habitats, attributed to the influx of summer spawning species. Diplodus sargus dominated catches from the exposed surf zone, and the timing of observations supports the growing consensus that sparid spawning is dictated by temperature, not season. The similitude of the observed species to those observed in warm temperate South Africa highlights the historical connection of the warm-temperate study area with warm-temperate South Africa, prior to the formation of the Benguela Current as a vicariant barrier. The classification of the study assemblage into established estuarine utilization categories showed that the surf zone hosted more exclusively marine species than comparable surf zones in South Africa, attributed to the absence of estuaries in southern Angola. However, the observation of the marine estuarine dependent Mugil cephalus in this study area devoid of estuaries suggests that estuarine dependency may be regionally specific for some taxa. It appears that the warm, sheltered, nutrient rich waters of Tombua Bay provide typically estuarine associated taxa with a suitable alternative, non-estuarine nursery habitat. This study provides evidence that the importance of estuaries as critical nursery habitats has been overemphasized for some warm-temperate coastal fishes. However, the absence of other marine estuarine dependent species from the study area suggests that some warm-temperate taxa do intrinsically rely on estuarine function for survival.
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Date Issued: 2017

The growth characteristics of sparid otoliths

Authors: Lang, Judy Brenda
Date: 1992
Subjects: Fishes -- Age determination , Otoliths , Sparidae
Language: English
Type: Thesis , Masters , MSc
Identifier: vital:5285 , http://hdl.handle.net/10962/d1005129 , Fishes -- Age determination , Otoliths , Sparidae
Description: The periodicity of formation of growth increments in the otoliths of South African sparids was validated by the oxytetracycline labelling technique. Intramuscular injections of oxytetracycline at a dosage of 250mg/kg marked the otoliths of laboratory held juvenile sparids, while a dosage range of 50 - 100mg/kg oxytetracycline, injected intramuscularly, marked adult sparids in the field. Laboratory held, larval sparid otoliths were marked by immersion for 24hrs a solution of 100-150mg/l alizarin complexone. Both daily (microstructural) and annual (macrostructural) growth increments were identified in the otoliths. The micro incremental pattern of deposition in the sparid otoliths conformed to the general pattern of otolith structure. Sparid otoliths consisted of a central opaque nucleus composed of multiple primordia. surrounding this nucleus were daily increments which decreased in width as the distance from the nucleus increased. Both check rings and subdaily increments were visible throughout the otolith. Minor environmental changes did not affect micro incremental deposition. Narrow opaque and wide hyaline annual growth zones were identified in sectioned sparid otoliths. Scanning electron microscope analysis of the annual growth zones revealed that microincrements within the opaque zone were narrowly spaced with prominent discontinuous phases. This resulted in the greater optical density and higher protein content of the zone. The hyaline zone was composed of widely spaced daily increments with prominent incremental phases accounting for the translucent nature of this zone. Opaque zone formation in the otoliths of many South African sparids was found to occur primarily during periods of reproductive activity and was shown to be indicative of slow otolith growth. The hyaline zone was formed after the spawning season, representative of fast otolith growth. The results of this study have resolved much of the controversy surrounding the rate of growth and time of formation of the opaque and hyaline growth zones in South African sparid otoliths.
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Date Issued: 1992

An assessment of the monkfish resource of Namibia

Authors: Maartens, Lima
Date: 2000
Subjects: Lophius -- Namibia Lophius
Language: English
Type: Thesis , Doctoral , PhD
Identifier: vital:5231 , http://hdl.handle.net/10962/d1005074
Description: Two monkfish species are caught off the coast of Namibia. These are Lophius vomerinus Valenciennes (1837) and L. vaillanti Regan (1903). L. vomerinus is the more abundant of the two and contributes approximately 99% to the total Namibian monkfish landings. The Namibian monkfish fishery is one of the largest and most valuable of its kind in the world. Two fishing fleets harvest the resource, viz. the monkfish and sole fleet and the hake directed fleet. In 1998 and 1999, monkfish were also harvested by one gillnet vessel that had an experimental right. In this study, the biology, abundance and exploitation patterns of monkfish were investigated and used as inputs into a stock assessment framework as a contribution towards the development of a management procedure for this species. Ground and sectioned otoliths and sectioned illicia were used to age Lophius vomerinus. The illicia provided more precise estimates of age, and growth was subsequently modelled using these age estimates. Growth in length and weight was best described by the threeparameter specialised von Bertalanffy model as Lt (cm TL) = 72.29 (1-e⁻°·¹⁴⁽t⁺°·³°⁾) and Wt (kg) = 3.96 (1-e⁻°·¹⁸⁽t⁺°·¹°⁾)²·⁹⁹ for males, and Lt (cm TL) = 111.98 (1-e⁻°·°⁸⁽t⁺°·³⁶⁾) and Wt (kg) = 6.92 (1-e⁻°·¹⁸⁽t⁻°·⁶⁴⁾)³·°³ for females. L. vomerinus is a slow-growing species with a life span in excess of 10 years. Reproductive activity was shown to occur throughout the year, with a slight peak during the winter months. The adult sex ratio of fish > 37 cm TL was biased towards females. Length-at-50% sexual maturity was attained at 32.1 cm TL for females and 23.7 cm TL for males. The rate of natural mortality was estimated at 0.15 year⁻¹, while fishing mortality rates during the 1970s, 1980s and 1990s were estimated at 0.01 year⁻¹, 0.04 year⁻¹ and 0.14 year⁻¹, respectively. Gillnetting for monkfish (300 mm stretched mesh) was highly efficient with a moderate bycatch of around 20% during the two years of operation. The main bycatch species were red crab, spider crab, squalid sharks, rays and Cape and Deep-water hake. The mean length of the monkfish caught in gillnets (67 cm TL) was significantly larger than the monkfish landed by the trawlers (38 cm TL) and less than 1% of immature fish were landed. Gillnet catch-per-unit-effort for monkfish fluctuated between 0.03 and 0.67 kg.day⁻¹.50 m net panel⁻¹, with a soak time of between one and sixteen days. More than 50% (by weight) of monkfish landed by monkfish and sole trawlers, consisted of fish below 36 cm TL. There was a significant increase in catches of juvenile monkfish during 1997 and 1998 in comparison to the period 1994 to 1996. Various types of rigid sorting grids were tested to release juvenile monkfish below 32 cm TL. Five grid designs were tested. These included an “Ex-it” grid with horizontal bars spaced at 55 mm, single grids with vertical and horizontal bars spaced at 55 mm and grids with circular openings of 110 and 168 mm in diameter. The most efficient design was the grid with circular openings of 110 cm in diameter, which ensured the escape of 66% of monkfish smaller than 31 cm TL. However, studies need to be undertaken to quantify the survival of released fish and to test the feasibility of using grid sorters on commercial monkfish and sole trawling gear. The monkfish resource was assessed by means of length cohort analyses, the Thompson and Bell predictive model and by way of a deterministic age-structured production modelling approach. The length cohort analysis models were sensitive to the rate of natural mortality and insensitive to changes in the terminal fishing mortality rate. These biases may, however, not be serious provided that estimates of abundance are used to reflect relative changes. Fish ranging between 26 and 59 cm TL are the most heavily exploited. The Thompson and Bell model predicted that the monkfish resource is exploited above MSY -levels and a reduction of approximately 40% in fishing effort would provide a higher yield. Yield-per-recruit ranged between 10 000 and 14 000 tonnes. Results should, however, be treated with caution, as the condition of steady state was not satisfied. The age-structured production model was tuned using trends in catch-per-unit-effort data, estimated by Generalised Linear Modeling, as well as relative abundance indices calculated from hake biomass surveys. The model was found to be sensitive to both the ‘steepness’ parameter h and estimates of natural mortality. The ‘depletion’ level of the monkfish resource is currently estimated to be 49%. Estimated coefficients of variation were high (> 63%) due to the lack of a consistent trend within the abundance indices to tune the model. Overall productivity of the monkfish resource was estimated to be approximately 16%, similar to other southern African demersal resources. Results of the risk analyses suggest that catches in excess of 7 000 tonnes may be unsustainable and that catches of 5 000 or 6 000 tonnes would decrease the risk of stock collapse and possibly lead to a recovery in the stock. Monkfish management strategies were reviewed and these were considered in relation to the results of this study. The following management recommendations were made: to follow the precautionary approach and implement a total allowable catch for monkfish; to implement rigid sorting grids as these would be the most appropriate way in which to reduce catches of juvenile monkfish; to restrict soak time, depth of operation and implement means to reduce ‘ghost fishing’ by gillnetting and finally, to develop a management procedure for Namibian monkfish with the main objective being the sustainable exploitation of the resource.
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Date Issued: 2000

Regional connectivity, differentiation and biogeography of three species of the genus Lutjanus in the western Indian Ocean

Authors: Morallana, Jonas Moqebelo
Date: 2014
Subjects: Lutjanus -- Indian Ocean , Biogeography -- Indian Ocean , Phylogeography -- Indian Ocean , Lutjanus -- Geographical distribution , Lutjanus -- Variation , Mitochondrial DNA , Animal genetics , Variation (Biology)
Language: English
Type: Thesis , Masters , MSc
Identifier: vital:5369 , http://hdl.handle.net/10962/d1013293
Description: Snappers of the genus Lutjanus are small to large predatory fishes occurring in inshore circumtropical and subtropical waters throughout the world. These fishes support fisheries across their distribution range. Within the Western Indian Ocean (WIO), previous studies on Lutjanus kasmira revealed limited spatial genetic differentiation, whereas Lutjanus fulviflamma showed high genetic connectivity. The phylogenetic relationships among WIO snappers are unknown. Previous studies in the Indo-Pacific (IP) did not include any WIO representatives. This study examined (1) the phylogeographic patterns in Lutjanus bohar, L. fulviflamma and L. lutjanus to understand the origins and factors influencing the distribution of diversity in the region, (2) how the physical environment, biological, and ecological factors influence genetic diversity, (3) the placement of WIO snappers in context to those from the IP, as well as the placement of taxa not included previously, (4) extent of differentiation among conspecifics from the two regions, and (5) the relationship of the Caesionidae to the Lutjanidae. Samples were sourced from across the WIO and from peripheral localities, where possible. DNA sequence data were generated from two mitochondrial gene regions (cyt-b and NADH-2) and a nuclear gene region (S7 intron 1). Data were analysed under a phylogeographic framework to examine genetic structure, diversity and differentiation among identified regions for each of the three species. Other sequence data were generated from two mitochondrial gene regions (COII and 16S rDNA) to examine the phylogenetic placement of WIO snappers in context of the IP snappers and the relationship of the Caesionidae to the Lutjanidae. Lutjanus bohar and L. fulviflamma displayed high genetic diversity, but lower diversities were observed for L. lutjanus. Genetic differentiation was observed between Mozambique and Maldives in L. bohar. Lutjanus fulviflamma was differentiated in South Africa, Mozambique, Mauritius and Thailand, while differentiation was observed between Kenya and Tanzania in Lutjanus lutjanus. Overall, low genetic differentiation and high connectivity were observed for each of the three species. This differentiation may result from intrinsic features of the species and extrinsic features of the environment, whereas the connectivity is mainly influenced by the pelagic larval duration. These patterns of differentiation are in accordance with a proposed vicariant biogeographic hypothesis for the origins of regional faunas of the IP. Phylogenies were similar to those published, with additional taxa not altering the previous groupings found. Conspecifics from the two regions clustered together, with varying degrees of differentiation among the WIO and IP, depending on the species. Members of the Caesionidae were nested within Lutjanidae, suggesting that morphological characters separating the two families are taxonomically insignificant. This affirms previous notions that the Caesionidae should be a subfamily within the Lutjanidae. This is the first multi-gene study, examining differentiation in multiple species of snapper over a wide geographic area in the WIO, and the results of this study could have potential implications for fisheries management and conservation.
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Date Issued: 2014

A study of the population dynamics, production and potential yield of the sardine Limnothrissa Miodon (Boulenger) in Lake Kariba

Authors: Marshall, Brian Eric
Date: 1987
Subjects: Fishes Lake Tanganyika sardine
Language: English
Type: Thesis , Doctoral , PhD
Identifier: vital:5191 , http://hdl.handle.net/10962/d1001967
Description: The limnology of Lake Kariba, especially those aspects that affect sardine biology, are described. The hydrological regime of the lake is seen as a major influence and may be one of the reasons why the fish are very much smaller in Kariba than they are in Lakes Tanganyika or Kivu. Growth was reassessed and there appeared to be a correlation between rates of growth and limnological parameters. In particular, the fish appeared to grow faster, but smaller, in the man-made lakes and this may be a consequence of food shortages brought about by their hydrological characteristics. Mortality rates were also much higher in Kariba and this tended to support the view that the lake is a relatively unsuitable habitat for the sardines. However, estimates of biomass, expressed in terms of lake volume, contradicted this as they were very similar in both Kariba and Tanganyika. The life history strategy of Limnothrissa in Kariba was therefore to reduce its size and increase its productivity in order to maintain the maximum possible biomass and its very high P/B̄ ratio was probably the means by which this was achieved. In terms of lake volume the predicted yields from the pelagic communities of Kariba and Tanganyika were very similar, equivalent to about 20 000 t annually for Kariba. This is close to the yield predicted by several empirical models and the fishery now appears to be entering a phase where increases in effort will not be matched by increased yields. The mechanisms for controlling effort in the fishery appear to be inadequate and particular concern was expressed about the lack of co-ordination between the Zimbabwean and Zambian fishery authorities in planning the development of this shared resource.
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Date Issued: 1987

Bioaccumulation and histopathology of copper in Oreochromis mossambicus

Authors: Naigaga, Irene
Date: 2003
Subjects: Mozambique tilapia , Copper , Marine toxins , Fishes -- Effect of water pollution on , Water -- Pollution -- Environmental aspects
Language: English
Type: Thesis , Masters , MSc
Identifier: vital:5234 , http://hdl.handle.net/10962/d1005077 , Mozambique tilapia , Copper , Marine toxins , Fishes -- Effect of water pollution on , Water -- Pollution -- Environmental aspects
Description: Cu is one of the most toxic elements that affect fish populations when the fish are exposed to concentrations exceeding their tolerance. To investigate the effects of elementary Cu on aspects of bioconcentration, histology and behaviour, O. mossambicus were exposed to 0 and 0.75 ± 0.20 mg/l of Cu for 96 hours (short-term study), and 0, 0.11 ± 0.02, 0.29 ± 0.02, and 0.47 ± 0.04 mg/l of Cu for 64 days (longterm study) under controlled conditions in the laboratory. For the long-term study fish were sampled for gills, liver, and kidney Cu accumulation analysis after 1, 32 and 64 days of exposure and after 1, 2, 4, 16, 32, and 64 days for gills, liver and spleen histology analysis. Cu accumulation was concentration-duration dependent with the highest accumulation capacity in the liver. A multifactor linear model was developed for the relationship between exposure dose, exposure duration and Cu accumulation in the organs with the liver model: Log L = 3.35 + 0.85W + 0.31T (r² = 0.892) giving a better fit than the gills: G = −35.09 + 10.58W + 17.58T (r² = 0.632). Where L = Cu accumulation values in the liver, G = Cu accumulation values in the gills (both in μg/g dry mass); W = exposure dose in water (mg/l); and T = exposure time (days). Using this model Cu accumulation in organs can be estimated when exposure concentration and duration is known. This model should be tested under different conditions to determine the potential of the model in monitoring Cu toxicity in the environment. Lesions were observed in the liver, gills and spleen in all Cu treatments at all exposure concentration and exposure durations. However, the incidence and the degree of alteration was related to the concentration of Cu and duration of exposure. The sequential appearance of lesions in the order of, hepatic vacuolar degeneration, fatty degeneration and necrosis indicated a gradual increase in liver damage with larger duration of exposure time and increasing Cu concentration. The initial lesions in the gills were manifested as hypertrophy and hyperplasia of the gill epithelium causing increase in the thickness of the secondary lamellae, mucous cell hypertrophy and proliferation, mucous hypersecretion, proliferation of eosinophilic granule cells and hyperplasia of interlamellar cells. With increase in exposure time, necrosis of the eosinophilic granule cells, lamellar oedema, epithelial desquamation and increase in severity of lamellar hyperplasia were observed. These lesions indicated an initial defence mechanism of the fish against Cu toxicity followed by advanced histological changes that were related to Cu concentration and duration of exposure. Changes in the spleen were haemosiderosis, increase in the white pulp and macrophage centres, reduction in the red pulp, and necrosis suggesting that fish exposed to environmentally relevant levels of Cu may be histopathologically altered leading to anaemia and immunosuppression. Regression analysis was used to quantify the relationship between the total activity of the fish, and duration of exposure. There was a gradual decline in fish activity related to Cu concentration and duration of exposure before introducing food into the tanks. There was a constant activity after introducing food in the tanks at the control and 0.11 ± 0.02 mg/l Cu exposure levels irrespective of exposure time. Analysis of covariance (ANCOVA) was used to test for the difference in slopes between treatments. There was no significant difference (p > 0.05) between slopes of the control and 0.11 ± 0.02 mg/l Cu, and between 0.29 ± 0.02 and 47 ± 0.04 mg/l Cu before and after introducing food in the tanks. The slopes of both the control and 0.11 ± 0.02 mg/l Cu were significantly different from those of 0.29 ± 0.02 and 0.47 ± 0.04 mg/l Cu (p < 0.05). There were significant differences in the mean opercular movements per minute between treatments (p < 0.05). There was hyperventilation at 0.11 ± 0.02 mg/l Cu i.e. 87 ± 18 opercular movements per minute (mean ± standard deviation) and hypoventilation at 0.29 ± 0.02 and 0.47 ± 0.04 mg/l Cu i.e. 37 ± 34 and 13 ± 6 opercular movements per minute compared to the control. Hypo- and hyperventilation were related to the lesser and greater gill damage, respectively. In conclusion Cu accumulation and effects on histology of the liver, gills and were related to the concentration of Cu in the water and duration of exposure showing a gradual increase in incidence and intensity with larger duration of exposure time and increasing Cu concentration. The fish were initially able to homeostatically regulate and detoxify Cu. However, as the exposure continued, the homeostatic mechanism appears to have failed to cope with the increasing metal burden causing advanced histological changes.
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Date Issued: 2003

An ecological study of territoriality in four Cichlid species resident on rocky shores near Monkey Bay, Lake Malawi

Authors: Sharp, Bradley John
Date: 1982
Subjects: Cichlids -- Nyasa, Lake , Cichlids -- Behavior
Language: English
Type: Thesis , Masters , MSc
Identifier: vital:5340 , http://hdl.handle.net/10962/d1005927 , Cichlids -- Nyasa, Lake , Cichlids -- Behavior
Description: This study centres on a diverse assemblage of epilithic algal grazing fish (17 cichlids and 2 cyprinids) found on the rocky shores near Monkey Bay, Lake Malawi. Diet overlap among these species is large, but competitive exclusion is apparently avoided by the species having different feeding structures, behaviour and distribution on the shore. In many respects the ecology and behaviour of the cichlid fishes inhabiting the rocky zones of Lake Malawi parallel those of coral reef fish. In both communities there are species which are highly territorial, resulting in resource subdivision and, in some cases, the development of algal gardens. As this behaviour has not been previously reported for cichlid species, this thesis describes the territoriality of the rock-dwelling cichlids of Monkey Bay, Lake Malawi, and poses three specific questions: 1. What is the function of territoriality? 2. How do the territorial species subdivide the space resource? 3. What prevents one species taking over all the available space? It is suggested that interspecific territoriality evolved in response to a shortage of food, and, at present, serves principally to defend an algal garden i.e. a food supply of high standing crop. The species studied are extremely site specific. The rocky shore is subdivided among the four species according to the rock configuration, size, algal mat composition and position on the shore, of the available sites. An experimental study of the space utilization of the two common territorial species, referred to as 'Pseudotropheus orange cheek' and 'Pseudotropheus aggressive', showed that suitable territory sites are in short supply and that these species are in competition for some sites. These results do not support those of Fryer (1959) who suggested that a superabundance of food enabled fish to coexist by sharing the same food resource. Indeed it now appears that a shortage of food may have been a major driving force during the recent evolution of the species studied.
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Date Issued: 1982

Mesopredator release and the effectiveness of camera traps for estimating mammal abundances in the Eastern Cape, South Africa

Authors: Taylor, Jonathan Michael
Date: 2016
Language: English
Type: Thesis , Masters , MSc
Identifier: http://hdl.handle.net/10962/3587 , vital:20527
Description: Remotely operated cameras (camera traps) have become an indispensable tool for many ecologists, particularly those studying rare and elusive animals. A plethora of camera trap makes and models are now commercially available, yet the effects of their varying design features on the quality and quantity of data recorded remains principally unknown. Better understanding of differing camera trap designs is needed before adequate management policies can be implemented, especially when the aim is to protect vulnerable and endangered species such as many carnivores. Habitat loss and human conflict has prompted worldwide declines of apex predator populations. Following this, many smaller predators have undergone population ‘explosions’ due to the lack of top-down forcing, a phenomenon known as mesopredator release. Land use changes in the Eastern Cape of South Africa have caused extensive degradation and fragmentation of the Subtropical Thicket Biome. In addition, coupled with anthropogenic persecution, apex predators including lions (Panthera leo), leopards (P. pardus), and brown hyaenas (Hyaena brunnea) have been extirpated from large areas of their historic range. Removal of these apex predators may provide opportunity for mesopredators, such as black-backed jackals (Canis mesomelas) and caracals (Caracal caracal), to be released from top-down forcing and possibly initiate trophic cascade effects. Therefore, using randomly distributed camera traps, my study aimed to explore the quality and quantity of data collected by different camera trap designs, and to investigate the mesopredator release hypothesis in the Eastern Cape of South Africa. A total of 2,989 trap nights was used to compare camera trap designs. Camera traps with narrow detection zones and fast trigger speeds (≤ 0.25 seconds) recorded a higher diversity of carnivores, but there was no significant difference in the relative abundances of carnivore species recorded by different camera trap models. A total of 19,659 trap nights was used to assess mesopredator relative abundance, occupancy, distribution and daily activity patterns at one site with, and one site without, apex predators. Consistent with the mesopredator release hypothesis, black-backed jackal relative abundance was significantly higher in the absence of apex predators, and this was supported by occupancy analyses. Further, black-backed jackal distribution was significantly concentrated in areas where apex predator activity was low, possibly indicating spatial avoidance. There was no significant difference in caracal relative abundance, occupancy, distribution, or daily activity between sites. These results provide the first indication of mesopredator release of blackbacked jackals in the Eastern Cape. The implications of black-backed jackal release including prey population structure, local extinctions, altered seed dispersal and disease dynamics are discussed.
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Date Issued: 2016

Distribution, habitat associations and conservation of the Eastern Cape rocky Sandelia bainsii (Perciform: Anabantidae) in the Great Fish River system

Authors: Sifundza, Delsy Sindy
Date: 2020
Subjects: Anabantidae -- South Africa -- Great Fish River , Perciformes -- South Africa -- Great Fish River , Labyrinth fishes -- South Africa -- Great Fish River , Fishes -- Effect of human beings on -- South Africa -- Great Fish River , Fish populations -- South Africa -- Great Fish River , Fish declines -- South Africa -- Great Fish River , Fish populations -- Monitoring -- South Africa -- Great Fish River , Anabantidae -- Evolution -- South Africa -- Great Fish River , Gene flow , Mitochondrial DNA , Microsatellites (Genetics) , Eastern Cape rocky Sandelia bainsii , Freshwater ecology -- South Africa -- Great Fish River
Language: English
Type: Thesis , Masters , MSc
Identifier: http://hdl.handle.net/10962/142692 , vital:38102
Description: In South Africa, freshwater ecosystems are under pressure due to increasing anthropogenic factors degrading river systems. The Cape Fold, the lower Southern Temperate Highveld and the Amatolo – Winterberg Highlands freshwater ecoregions contain some of the heavily impacted river systems in the country. One such river system is the Great Fish River system, which has been affected by anthropogenic modification (hydrological modification, water pollution and invasion by non-native fish species). These modifications have raised conservation concerns on an imperilled anabantid fish, the Eastern Cape rocky Sandelia bainsii that is confined to the Kat and Koonap rivers, which are tributaries of the Great Fish River. Historically, the species was reportedly common and abundant, with a range spanning across seven river systems (Kowie, Great Fish, Keiskamma, Igoda, Gxulu, Buffalo and Nahoon rivers) in the Eastern Cape Province. However, surveys have indicated that the species has experienced decline in population size and distribution range, with localised extirpations being reported. This resulted in its listing on the IUCN Red List of threatened species as Endangered. The proposed shale gas exploration and potential infrastructure development in the Karoo basin, which encompasses the headwaters of the Kat River, represent a potential future threat to the remnant populations of this species. The aim of the present study was to review the past and present distribution range of S. bainsii, determine the habitat associations and assess the conservation of S. bainsii in the Great Fish River system. This information is essential for informing conservation and management decisions for this species in the Great Fish River system. This study undertook a comprehensive survey of the Kat and the Koonap rivers in 2017, and augmented this information with data from more recent surveys that were conducted from 2009 - 2014 to map the distributions freshwater fishes in the Great Fish River system. Data from these recent surveys (2009 – 2017) were compared with historical records (1961 – 2005) obtained from the South African Institute for Aquatic Biodiversity to evaluate changes in distribution patterns of S. bainsii. Historical records indicated that S. bainsii occurred at 11 localities in the Kat River and three localities in the Koonap River. Data from recent surveys indicated that the species has persisted at these historical localities, except one locality in the Koonap River where no individuals of S. bainsii were captured, despite the use of multiple sampling approaches and gears. Although the species still persists at two of the three historical localities in the Koonap River, the population sizes have considerably declined as the species was reportedly in high abundance at these localities in the 1980s. Factors threatening the continued existence of this species in the Koonap River likely include non-native species, extreme drought conditions and the associated excessive abstraction of water which has resulted in the drying of some of the refugia pools where the species was historically common and abundant. In contrast to the Koonap River, the 2017 survey indicated that in the Kat River, S. bainsii had a similar distribution range compared to historical records. The species occurred at 11 of the 41 localities that were sampled in the Kat River, and the sampled populations consisted of all size classes. Sandelia bainsii occurred with other native fish species in the system, including Labeo umbratus, Enteromius anoplus and Glossogobius callidus. A comparison of historical and recent data indicates that non-native fishes have likely not expanded their ranges in the Kat River. This is likely due to the presence of weirs and dams that have prevented upstream movement of non-native fish species L. aeneus, C. gariepinus and T. sparrmanii which are now abundant in the lower Kat and mainstem Great Fish River. Surveys from the present study indicated that although S. bainsii still persists within the Kat River, there are a number of factors that pose a considerable threat to the continued existence of this species in the Great Fish River system. Chapter 3 evaluated the habitat associations of S. bainsii based on 10 physical and chemical variables and distribution data collected from 30 localities in the Upper Kat River and seven of its tributaries. A non-metric multidimensional scaling model was used to assess the distribution patterns of S. bainsii in relation to environmental variables. Furthermore, a negative binomial generalised linear model (GLM) was used to assess the relationship between the abundance of S. bainsii and environmental variables. Results from the present study indicated that S. bainsii was a habitat generalist as the distribution of this species showed no specific association with any of the habitat variables that were considered in this study. The species occurred in a wide range of habitats, including rocky sections in the upper Kat River and its tributaries as well as the mainstem sections. The GLM however indicated that the abundance of S. bainsii was negatively associated with increasing conductivity. In addition, the Kat River contains multiple weirs of variable sizes. Future studies should therefore evaluate the effects of these weirs on population fragmentation, gene flow and long-term evolutionary potential of S. bainsii through the application of techniques such as mitochondrial DNA and microsatellites.
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Date Issued: 2020

Towards understanding the effect of size variation on the aggressive and feeding behaviours of juvenile dusky kob Argyrosomus japonicus (Pisces: Sciaenidae)

Authors: Babane, Siviwe Elvis
Date: 2018
Subjects: Argyrosomus -- Feeding and feeds , Aquaculture , Fishes -- Cannibalism , Fishes -- Feeding and feeds
Language: English
Type: text , Thesis , Masters , MSc
Identifier: http://hdl.handle.net/10962/59592 , vital:27629
Description: Many studies have been conducted on the effect of size-grading in other fish species. However, there is a paucity of scientific information on the effects of size variation on cannibalism of juvenile dusky kob. Thus, a study focusing on the effect of size variation on juvenile dusky kob aggressive and feeding (browsing) behaviours was conducted. Three separate groups of hatchery-reared juvenile dusky kob of were obtained from Oceanwise (Pty) Ltd for use in a series of three experimental trials. In all trials, juvenile fish of the same age were size-graded and the COV-value was used to determine the size variation. The focal fish (largest fish) was exposed to groups of fish with different size variation for 30-min. behavioural observations before and after feeding in randomised trials. The first experimental trial (Chapter 2) quantified the effect of increasing size variation and observation time on the aggressive and browsing behaviours of juvenile dusky kob. On average, juvenile dusky kob weighed 3.60 ± 0.68 g fish-1 and measured 5.8 ± 0.41 mm. Each focal fish was observed (a) before feeding in the morning, (b) 2 h after feeding, (c) 6 h after feeding and (d) 12 h after feeding. Fish increased browsing behaviours (averaging 6.60 ± 0.56) and decreased intimidating aggressive behaviours (18.60 ± 1.39) 12 h after feeding. Other aggressive behaviours occurred but did not differ between observation times. Aggressive and browsing behaviours positively correlated with size variation variables, predominantly, 12 h after feeding. An average frequency of 19 chases were observed positively correlated with size variation, followed by average frequencies of 17 body bites and browses, and 11 tail bites per 30 min. Some behaviours including average frequencies of 0.2 chases, 4 tail bites, 2.4 intimidating and 0.3 browsing behaviours negatively correlated with the size variation, generally closer to the last meal. These preliminary observations thus showed that fish have become hungry approximately 6-12 h after feeding and substituted certain behaviours for others as time after feeding passed and as size variation increased. The second experimental trial (Chapter 3) consisted of the observations further testing the relationship between aggressive behaviours and size variation of juveniles of dusky kob averaging 0.43 ± 0.27 g fish-1. The focal fish was exposed to groups of fish of four size variation (COV) treatments for observations before and 12 h after feeding. Aggressive behaviours positively correlated with size variation both before and 12 h after feeding. An average frequency of 437 body bites positively correlated more often with COV, followed by average frequencies of 365 intimidating behaviours and 199 tail bites per 30 min., respectively, before and 12 h after feeding. The least often exhibited aggressive behaviours averaged 26 chases while positively correlating with size variation on the times specified. An average frequency of 311 intimidating behaviours before and after feeding including average of 28 tail bites after feeding negatively correlated with size variation. This may relate to shift of behaviours depending on the needs and capacity of the fish. Apparently, aggressive fish can change its behaviour as a function of COV-values rather than the mean size of the other fish. The third trial (Chapter 4) investigated the effect of the aggressor’s (focal fish) size in relation its aggressive and browsing behaviours to other fish (non-focal fish). Juvenile fish used for this trial, on average, weighed 30 ± 7.63 g fish-1. Aggressive and browsing behaviours were observed in four treatments of a) high COV and mean weight below, b) low COV and mean weight less, c) high COV and mean weight equivalent to and d) low COV and mean weight higher than that of the focal fish. Increased frequencies of aggressive and browsing behaviours per 30 min. occurred in treatment A, sharing similar frequencies in treatment C, compared to the other treatments (B and D) which shared certain frequencies. The intimidating behaviours predominated, followed by browsing, body bites, chases and tail bites, respectively. The results of the overall study suggest that the time passed after feeding and increasing size variation and differences facilitated aggressive and browsing behaviours in juvenile dusky kob. Dusky kob showed increasing aggressive behaviours as early as in the first two weeks after hatching, averaging 0.43 ± 0.27 g fish-1 with the frequency correlating with size differences. Consistent size-grading technique in the same-age fish should be used to manage size variation associated with aggressive behaviours. The period of about 4-6 h after feeding may explain the noticeable increased aggressive and browsing behaviours. Thus, fish should be fed immediately before or after evacuation of their guts to maintain less-aggressive behaviours of juvenile dusky kob. Fish generally increased aggressive and browsing acts before and long time after feeding than closer to after feeding. The study has provided the fundamental scientific groundwork for fish farmers and future researchers can further explore size variation, time after feeding and gut evacuation rate as critical components of aggressive behaviours. The scientific knowledge of aggressive and cannibalistic behaviours has essential application in farming management to achieve improved survival and growth rates in juvenile fish.
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Date Issued: 2018

The role of microhabitats within mangroves: an invertebrate and fish larval perspective

Authors: Vorsatz, Lyle Dennis
Date: 2020
Subjects: Mangrove ecology -- South Africa , Mangrove forests -- South Africa , Niche (Ecology) , Rhizophora mucronata , Acanthaceae , Rhizophoraceae , Fishes -- Larvae -- South Africa , Aquatic ecology -- South Africa
Language: English
Type: text , Thesis , Doctoral , PhD
Identifier: http://hdl.handle.net/10962/167644 , vital:41499
Description: Microhabitats provided through structural complexity are central for the diversity, productivity, connectivity and niche differentiation within and among ecosystems. Mangrove forests afford juvenile fish and invertebrates with nursery and recruitment habitats, facilitated by the fine scale configuration of their specialised root systems. Although the importance of mangroves for resident and transient juveniles is well recognised, the roles that mangrove microhabitats play for larvae is not yet comprehensively understood. This study aimed to determine how microhabitats with varying degrees of complexity influence the composition, abundance and distribution of larval communities that inhabit mangrove forests and the physiological responses of larvae to acute temperature variations in relation to ontogenetic stage and microenvironment exposure. Two relatively pristine study sites were selected to represent a warm temperate and subtropical mangrove system in the Eastern Cape and KwaZulu-Natal on the east coast of South Africa, respectively. The differences in complexity among the root systems of Rhizophora mucronata, Avicennia marina and Bruguiera gymnorhiza were assessed using 3D scanning and the computed 3D models were then analysed using four complexity metrics. Results indicated that A. marina is the most complex in terms of surface-volume ratio, R. mucronata has the most interstitial space among its roots and B. gymnorhiza and R. mucronata differ in their fractal dimensions. Larvae collected in each microhabitat at each site using light traps showed that, despite temperature and salinity homogeneity across microenvironments, spatio-temporal differences occurred in both fish and invertebrate assemblages. This trend suggests that microhabitat structural complexity exerts an influence on larval community composition by acting as a microscape of available habitat, which ensures ecological linkages within and among the mangrove forest and adjacent ecosystems. In addition, the oxygen consumption rates of mangrove-associated brachyuran larvae varied according to mangrove microhabitat, whereby larvae collected at less complex environments had the highest metabolic rates at increased temperatures. Moreover, ontogenetic shifts in physiology were prevalent as older brachyuran larvae were more eurythermal than earlier stages, suggesting that thermally stressful events will have a greater impact on recently spawned larvae. Overall, the interstitial spaces within individual root systems are the most important complexity measure, as utilisation of these mangrove microhabitats is scale-dependent, and larvae will most likely occupy spaces inaccessible to large predators. Likewise, microscale variation in the environmental conditions and ontogenetic stage of brachyuran larvae within the mangrove microscape, can amplify the physiological responses to rapid temperature variations. Results suggest that early stage larvae are the most vulnerable to mass-mortality, and if thermally stressful events increase in frequency, duration and magnitude, the larval supply for the successful recruitment into adult populations could be under threat. Through linking how mangrove microhabitat complexity influences larvae in terms of community metrics and physiology, this study paves the way for further advancement of our understanding of how microscale processes emerge into meso- and macroscale patterns and influence the stability and functioning of highly productive ecosystems.
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Date Issued: 2020

Biology, population dynamics and management of carpenter (Argyrozona argyrozona) an endemic South African reef fish

Authors: Brouwer, Stephen Leonard
Date: 2005
Subjects: Reef fishes -- South Africa Sparidae -- South Africa
Language: English
Type: Thesis , Doctoral , PhD
Identifier: vital:5241 , http://hdl.handle.net/10962/d1005084
Description: Carpenter, Argyrozona argyrozona (Valenciennes, 1830), is an endemic South African sparid fish. They form an important component of the commercial linefishery on the South African east coast, where they are the third most important species landed. Recent investigations revealed that the catch per unit effort (cpue) of this species has declined markedly since the early 1900’s. Despite these declines and the importance of this resource, remarkably little biological information on this species exists for providing management advice. This thesis investigates the life history of carpenter, particularly those aspects that are used for management. This includes an investigation into the stock distribution and identification of nursery areas, and an assessment of age, growth, reproduction and movement patterns. Age and growth was assessed using methods based on both otoliths and mark-recapture. Transverse sagittal sections from the Tsitsikamma National Park showed clear opaque and translucent growth increments. Marginal growth zone analysis and mark-recapture of chemically tagged fish (Oxytetracycline) revealed that these were deposited on an annual basis: opaque in summer and translucent in winter. A. argyrozona were found to be long lived (up to 27 years) and slow growing. Within reader (between counts) and between readers average percent error (APE) was 5.3 and 1.8, respectively, showing that readability of carpenter otoliths is high. Comparison between whole and sectioned otoliths showed that the former significantly under-estimated the age of fish older than 10 years (p<0.01). A large proportion (68%) of the individual growth rates derived from mark-recapture data were below those predicted by the otolith based von Bertalanffy growth model (p<0.01). This was attributed to the negative influence of external tags, as hydroids, frequently occurring on the tags of recaptured fish, were observed to cause severe lesions and in some cases, extensive fin damage. This brings into question the use of mark-recapture studies to calculate growth of some species. The effects of sampling design and sample size on age and growth estimation were assessed. The minimum sample size required to accurately estimate growth and mortality, and the effects of using either random or stratified sampling procedures were tested. Decimal and integer ageing both produced similar estimates of von Bertalanffy growth parameters, growth curves, spawner biomass-per-recruit (SB/R) and fishing mortality (F) estimates. Sampling monthly throughout the year and collecting data in a single large sample provided similar growth curves, von Bertalanffy, F and SB/R estimates. The data showed that estimates based on less than 300 random samples were unreliable. However, accurate growth parameter estimates were achievable with less than 200 samples if the sample was stratified with 10 or more samples per 2 cm size class. An investigation into the reproductive biology of A. argyrozona within the Tsitsikamma National Park revealed that they were serial spawning late gonochorists. The size at 50% maturity (L₅₀) was estimated at 292 and 297 mm FL for females and males, respectively. Both monthly gonadosomatic indices and macroscopically determined ovarian stages strongly suggest that A. argyrozona within the Tsitsikamma National Park spawn in the austral summer between November and April. The presence of post-ovulatory follicles (POF's) confirmed the six month spawning season, while monthly proportions of early (0-6 hour old) POF's showed that spawning frequency was highest (once every 1-2 days) from December to March. Although spawning season was more highly correlated to photoperiod (r = 0.859) than temperature (r = -0.161), the daily proportion of spawning fish was strongly correlated (r = 0.93) to ambient temperature over the range 9-22⁰C. Both spawning frequency and season increased with fish length. As a result of the allometric relationship between annual fecundity and fish mass a 3 kg fish was calculated to produce 5 fold more eggs per kilogram of body weight than a fish of 1 kg. In addition to producing more eggs per unit weight each year, larger fish also produce significantly larger eggs. Adult emigration and larval dispersal of A. argyrozona from the Tsitsikamma National Park (TNP), South Africa, were investigated using mark-recapture data and Acoustic Doppler Current Profiler measurements of currents. Tagging data showed that adult carpenter were mainly resident, with a small proportion (7%) leaving the TNP in both easterly and westerly directions. No relationship was found between fish movement patterns and fish size or time-at-liberty. Current patterns suggest that eggs and larvae spawned within the TNP are mainly transported eastwards towards established nursery grounds; the median estimated distance moved was 299 km (range 42-561 km) in 30 days (time to flexion). Given this pattern of ichthyoplankton dispersal together with the fact that adult carpenter within the TNP display a high degree of residency and that they are much more abundant than in adjacent fishing grounds (cpue = 23 times greater), it appears that the TNP protects a viable carpenter spawner population capable of seeding adjacent fishing grounds. Fishery independent biomass surveys and commercial linefish catch returns were used to elucidate the spatial patterns of A. argyrozona distributed along the South African continental shelf. Two distinct areas of abundance were determined, one on the central and the other on the eastern Agulhas Bank. Tagging studies revealed little exchange between them. Two distinct nursery areas were identified. These data suggest that in each area juvenile A. argyrozona settle and move inshore, and then move offshore as they grow. Otolith readability and growth rates varied between regions, with fish from the Eastern Cape having the lowest average percentage error and the slowest growth rates, readability decreased westward. L₅₀ varied between the central and eastern Agulhas Bank as did mass at length. Based on the distribution of carpenter, variability in otolith readability, mass at length, variation in growth and size at maturity, it is concluded that carpenter exist as two separate stocks, one on the central Agulhas Bank and the other on the eastern Agulhas Bank. SB/R, fecundity-per-recruit (Egg/R) and yield-per-recruit (Y/R) models were used to model both South African carpenter stocks. Owing to the allometric relationship between annual fecundity and individual size, Egg/R ratios were between 40 and 74% of SB/R at equivalent F. Egg/R ratios account for allometric increases in fecundity with size/age, and are therefore regarded as more accurate estimates of reproductive potential, and biological reference points for per-recruit analysis should wherever possible be based on this quantum. It is shown that the current length at first capture (lc) (250 mm TL) and F (at M = 0.1) will reduce Egg/R to 6.41% of the pristine value in the Eastern Cape and between 6.06 and 14.15% on the central Agulhas Bank, indicating that both stocks are heavily over exploited. An increase in lc from 250 to 350 mm TL and a 70% reduction in commercial fishing effort is recommended to attain a target reference point of 40% Egg/RF=0. Bag frequency analysis indicates that a reduction in daily bag limit from 10 to 4 fish.person¹.day⁻¹ would effect an equivalent reduction in recreational F. The trawl bycatch of carpenter is only 3% of the reported line catch, consequently restrictions to this fishery are not recommended.
Full Text:
Date Issued: 2005

A nutritional evaluation of effluent grown algae and zooplakton as feed ingredients for Xiphohorous helleri, Poecilia reticulata and Poecilia velifera (Pisces : Poeciliidae)

Authors: Potts, Warren M
Date: 1998
Subjects: Poeciliidae , Poeciliidae -- Nutrition , Zooplankton , Algae , Poeciliidae -- Feeding and feeds
Language: English
Type: Thesis , Masters , MSc
Identifier: vital:5306 , http://hdl.handle.net/10962/d1005151 , Poeciliidae , Poeciliidae -- Nutrition , Zooplankton , Algae , Poeciliidae -- Feeding and feeds
Description: The aim of this study was to evaluate the nutritional value of algae and zooplankton grown in an algal integrated ponding system for poeciliids. The available information on the nutritional requirements of poeciliids was compared with a proximate analysis of the algae and zooplankton. The effluent grown algae and zooplankton had a crude protein value of 41.47 ± 0.2% and 36.84 ± 0.3%, a lipid content of 4.8 ±. 0.4% and 11.1 ± 0.8% and a carbohydrate content of 35.13 ± 0.8% and 31.06 ± 0.6% respectively. These values compared favourably with those of the known nutritional requirements of poeciliids. To test if the nutritional value of the algae and zooplankton in the AlPS was constant, the species composition of the algae and the crude protein content of the algae and zooplankton in the high rate oxidation ponds were measured monthly and bi-weekly for a year respectively. The species composition remained fairly stable for the duration of the experiment and the average protein composition of the algae and zooplankton was 43.4 ± 4.4% and 38.6 ±2.8% respectively. This indicated that the algae and zooplankton in the AlPS provided high protein biomass through the year. The quality of the effluent grown algal and zooplankton biomass was evaluated by analysing their amino acid composition and comparing it with the amino acid composition of the body tissue of X. helleri. With respect to the amino acid composition of the body tissue of X. helleri, the amino acid profile of the algae had a 69% and the zooplankton a 63% similarity. The quality of the pure algal and zooplankton protein was also tested biologically, by feeding them directly to poeciliids during a ten week growth trial. The algae and zooplankton diets did not result in adequate growth compared to poeciliids which were fed a formulated control diet. The initial growth trial also evaluated the effect of processing on the chemical composition of the algae and its biological effect on fish fed with it. There were no significant differences in the chemical composition of fresh and sun dried algae and this was reflected in the growth rates of the fish which did not differ significantly. Freeze dried algae had a lower crude protein content than fresh and sun dried algae and a poorer amino acid composition. Fish fed freeze dried algae exhibited poorer growth and survival in comparison to the other treatments. The gut transit times of X. helleri and the gastric evacuation times of poeciliids were determined using colour dyes incorporated in the diet and by sacrificing fish at predetermined intervals after feeding respectively. The gut transit time of X. helleri fed a sun dried algal diet and a formulated diet was 225 ± 8.55 minutes and 261.93 ± 10.86 minutes respectively. The gastric evacuation times of X. helleri, P. reticu/ata and P. velifera were 7, 9 and 8 hours respectively. Since the maximum amount of food in the hindgut after feeding was detemined to be 3, 5 and 3 hours in X. helleri, P. reticulata and P. velifera respectively, fish were sacrificed at these times in the digestibility study. The digestibility of sun dried algae was determined using 1 % chromic oxide as an internal marker in the algae. The apparent crude protein digestibility of sun dried effluent grown algae ranged from 65%-75% in the three poeciliid species. Based on the results of the chemical and biological analysis of the algae and zooplankton, conventional diets incorporating algae at 5% and 20% protein inclusion levels were formulated. These diets and a treatment in which zooplankton, reared in the AlPS were fed as a dietary supplement to a formulated diet were fed to poeciliids for twelve weeks. No significant differences in the growth of poeciliids fed any of the test diets were observed. It was concluded that the algae could be incorporated into poeciliid formulated diets up to level of 20% protein inclusion without any negative effect on the growth of the fish. The chemical and biological evaluation of the algae suggested that it had a similar nutritional quality to soyabean meal. Poeciliid growth was not enhanced with a zooplankton supplement, however a possible low feeding rate by poeciliids on the zooplankton as a result of their small size may have affected the result. The colour enhancement potential of effluent grown algae and zooplankton was evaluated biologically in ten and twelve week growth trials using visual observation (31 people) and by using a chromameter. While pure, sun dried algae significantly enhanced the colour of P. reticulata, no significant differences in the colour of poeciliids were observed or recorded when fish were fed diets incorporating sun dried algae up to levels of 20% protein inclusion. The effect of effluent grown algae and zooplankton on poeciliid health was also tested biologically in the ten and twelve week growth trials. The high mortalities (75%-84%) recorded for X. hel/eri when fed the pure algal and zooplankton diets were considered to be as a result of the nutritional inadequacy of the diets since there were significantly less mortalities in fish fed the formulated control diet and 63% of the fish that died during the course of the trial were emaciated. In addition, fewer mortalities (10%-40%) were recorded in X. hel/eri fed the nutritionally adequate formulated diets in the twelve week growth trial. No symptoms of disease were recorded in the twelve week growth trial and the algae was considered to have no toxicological or pathological effects on poeciliids. Centrifugation, sand filtration, sedimentation, microstraining and biological harvest were evaluated as methods of small scale algal harvest from the high rate oxidation ponds. Algae could be harvested most efficiently with little associated labour by sedimentation (without flocculating agents) and by microstraining with 60IJm mesh. Effluent grown algae can replace conventional feed ingredients up to a level of 20% protein inclusion without negatively effecting the growth, colour, health or survival of poeciliids.
Full Text:
Date Issued: 1998

Towards a new approach for coastal governance with an assessment of the Plettenberg Bay shore-based linefishery

Authors: King, Claire Margaret
Date: 2006
Subjects: Fishery management -- South Africa -- Plettenberg Bay , Fisheries -- South Africa -- Plettenberg Bay , Coastal zone management -- South Africa -- Plettenberg Bay
Language: English
Type: Thesis , Masters , MSc
Identifier: vital:5326 , http://hdl.handle.net/10962/d1005172 , Fishery management -- South Africa -- Plettenberg Bay , Fisheries -- South Africa -- Plettenberg Bay , Coastal zone management -- South Africa -- Plettenberg Bay
Description: The overall aim of this thesis, as required by the funders, was to provide research that would contribute towards the development of a bay management plan, specifically information on the local fisheries. The thesis therefore includes an assessment of the local shore-based linefishery in terms of catch and effort and socio-economics, and the development of indicators from this information with which to assess the sustainability of the fishery. Finally an implementation strategy for an integrated coastal management approach for local resource governance is proposed The shore-based linefishery of Plettenberg Bay was assessed through a combination of roving creel and access point surveys which included questions aimed at the quantification of total effort, total catch and cpue, as well as the spatial trends in catch and effort. Angler demographics as well as opinions and knowledge of current fisheries regulations were obtained and the efficiency of the fishery inspectorate was assessed. The survey period extended from August 2003 to September 2004 during which 1189 angler interviews were conducted. Catch data obtained during this study was compared to catch data gathered during a research tagging program conducted in an area closed to fishing (Tsitsikamma National Park) and a semi-open area (Rebelsrus – Cape St. Francis), thereby highlighting differences in species composition, abundance and size distribution of certain species between areas of differing fishing pressures. The fishery surveys revealed that the shore-based fishery is primarily recreational (99%) and dominated by white males. Most anglers agreed with the current fisheries regulations (60%) and admitted to abiding by them, however when tested on the regulations of their target species, their knowledge was poor. Effort in the fishery was highly seasonal with peaks coinciding with major school holidays. Total annual effort was estimated at 102 566 angler-hours, with distinct spatial patterns in effort. Total annual catch for the Plettenberg Bay shore-based linefishery was estimated at 31 217 fish.year⁻¹ with a total mass of 13.6 tons. Thirty-six fish species (26 teleost species and 10 elasmobranchs species) were identified during the survey period with Blacktail Diplodus capensis, Strepie Sarpa salpa, Red tjor-tjor Pagellus natalensis, Shad Pomatomus saltatrix and Sand steenbras Lithognathus mormyrus being the five most commonly caught species. Only 32% of interviewed anglers were successful in catching a fish with just 22% catching their primary target species. In addition, a large proportion of the anglers (69%) reported a decline in catch rate, with most blaming the commercial sector as a reason for the decline. The overall catch rate was (cpue) 0.374 fish.angler.hour⁻¹ or 170 grams.angler.hour⁻¹, considerably lower than that obtained from the fishery exempt area (TNP = 1. 02 fish.angler.hour⁻¹) and the partially exploited area (Rebelsrus = 0.91 fish.angler.hour⁻¹). In terms of species composition the most obvious difference between the three areas was the low proportion of non-migratory reef-associated species like red roman, poenskop, John brown, santer and bronze bream in Plettenberg Bay. Size comparisons revealed that the majority of species (particularly reef-associated species) were larger in the TNP than both the semi-exploited (Rebelsrus) and exploited area (Plettenberg Bay). Collectively theses findings suggest that certain species have been locally depleted, that recreational fishing has impacted heavily on the fish stocks and that even partial closure or limited access to an area can offer protection. From the results key issues were identified and sustainability indicators proposed according to the three sustainability domains (ecological, institutional and social) proposed by Pajak (2000). Within the ecological domain the most pertinent issue was the low catch rate, particularly for reef-associated species. Indicators to track these issues included: percentage of successful trips (where fish were caught), percentage of anglers that reached their daily bag limits and the proportion of the overall catch that comprised larger, more desirable species. Institutionally the most pertinent issue was the apparent inability of management institutions to manage effectively marine resources within Plettenberg Bay. Indicators within this domain included the proportion of anglers who were inspected, the existence of a localised management plan and an associated monitoring programme. Socially the fishery proved to be fairly sustainable. Indicators included in this domain were the proportion of subsistence anglers in the local fishing community, the percentage of correct answers pertaining to current fishery regulations, the level of noncompliance and the percentage of undersize fish retained. Aggregation of all the indicators within a sustainability matrix revealed that the Plettenberg Bay shore-based linefishery was unsustainable and thus requires increased local management effort. Since there is no local management strategy in place, an integrated coastal management approach for the governance of the coastal resources in Plettenberg Bay has been proposed. The development of a Coastal Management Plan and a subsidiary Bay Management Plan provide the frameworks within which management strategies can be put into operation.
Full Text:
Date Issued: 2006

Understanding biotic interactions in invaded pond communities in the Sundays River irrigation network, South Africa

Authors: Mofu, Lubabalo
Date: 2020
Subjects: Mozambique tilapia -- South Africa -- Sundays River (Eastern Cape) , Western mosquitofish -- South Africa -- Sundays River (Eastern Cape) , Gobiidae -- South Africa -- Sundays River (Eastern Cape) , Clupeidae -- South Africa -- Sundays River (Eastern Cape) , Reservoirs -- South Africa -- Sundays River (Eastern Cape) , Zooplankton -- South Africa -- Sundays River (Eastern Cape) , Freshwater ecology -- South Africa -- Sundays River (Eastern Cape) , Biotic communities -- South Africa -- Sundays River (Eastern Cape) , Fishes -- Effect of temperature on -- South Africa -- Sundays River (Eastern Cape) , Stable isotopes , Relative Impact Potential
Language: English
Type: Thesis , Doctoral , PhD
Identifier: http://hdl.handle.net/10962/167089 , vital:41436
Description: The Sundays River valley irrigation ponds provide a unique opportunity to investigate biotic interactions within a biological invasions context, as they contain both native and non-native fish species. This study focusses on two native species (Glossogobius callidus and Gilchristella aestuaria) and two non-native species (Oreochromis mossambicus and Gambusia affinis). The ecology of the ponds was driven by physico-chemical variables, mainly temperature, but the interactions between fishes were a complex interplay between temperature, pond community ecology and food web structure. Seasonal changes in temperature and subsequent fluctuations in water levels resulted in changes in zooplankton community. Chlorophyll-a, temperature, G. callidus and G. affinis were the drivers of the seasonal changes in macroinvertebrate composition. Stable isotope analysis identified substantial ontogenetic dietary shifts in all species, corresponding to changes in body size. Stable isotope analysis revealed that the niche space occupied by G. affinis was broad and overlapped with that of the other three focal species. Stable isotope metrics showed that G. affinis and O. mossambicus utilised a wide range of resources compared to G. callidus and G. aestuaria. Stomach content analysis showed that G. callidus, O. mossambicus and G. affinis fed predominantly on benthic resources, while G. aestuaria fed mainly plankton resources. Functional response experiments revealed that G. callidus and G. affinis both displayed Type II functional responses. In single fish trials, G. affinis had significantly higher functional responses than G. callidus. In heterospecific G. callidus-G. affinis combinations the functional response of G. callidus was reduced by the presence of G. affinis, whereas, this combination greatly enhanced G. affinis functional response magnitudes. The functional response of G. callidus, O. mossambicus and G. affinis under two temperature treatments along with fish abundance data was used to determine temporal differences in the ecological impacts of each fish species between seasons. The relative impact potential of O. mossambicus was consistently higher than that of G. callidus and G. affinis. This study demonstrates how seasonal temperature fluctuations affect the relative impact capacities of introduced species. Overall, this thesis showed that high temperature along with life-history traits contributes to the biotic interactions between native and non-native species in novel environments.
Full Text:
Date Issued: 2020

Reproductive behaviour of the skunk clownfish, Amphiprion akallopisos, under captive conditions

Authors: Haschick, Rory Dean
Date: 1998
Subjects: Anemonefishes -- Spawning , Amphiprion -- Reproduction , Fishes -- Reproduction , Hatchery fishes
Language: English
Type: Thesis , Masters , MSc
Identifier: vital:5316 , http://hdl.handle.net/10962/d1005161 , Anemonefishes -- Spawning , Amphiprion -- Reproduction , Fishes -- Reproduction , Hatchery fishes
Description: The objectives of the study were to determine whether or not behaviour could be used to predict spawning in Amphiprion akallopisos, and to document the behaviour of this species under various environmental conditions in captivity. The spawning behaviour of A. akallopisos was studied and quantified. Three behaviour patterns - belly touching, nest cleaning by the female and mutual nest cleaning (by the male and the female) were identified as predictors for spawning. The reproductive behaviour of A.akallopisos under three photoperiods was investigated. The photoperiods were: 14L:10D, 10hr15minL:13hr45minD and a natural photoperiod cycle condensed into three months. A. akallopisos maintained under 14 L:10D exhibited a significantly higher frequency and duration of chasing, nest cleaning and total interaction compared to fish kept under 10hr15minL:13hr45minD. A photoperiod of 14L:10D was selected for further studies. As manipulation of photoperiod did not induce spawning, GnRHa was administered to the fish in the diet at levels of 10, 20, 40 and 80 μg/kg BW. Control groups were fed untreated food. None of the dosages were successful in inducing spawning, or spawning behaviour in A. akallopisos. It is possible that the method of hormone application was not suitable for this species. It is also possible that behaviour may regulate blood hormone levels as opposed to endocrine status influencing behaviour. In the third trial, A. akallopisos was maintained with, and without sea anemones in order to determine whether or not anemone hosts are necessary for spawning. The presence of anemones did not induce spawning and A. akallopisos kept without anemones exhibited significantly more interactive behaviour than fish kept with hosts. Spawning of A. akallopisos at a later date without anemones suggests that anemones are not necessary for spawning in A. akallopisos. Light intensity was investigated as a cue for spawning. The reproductive behaviour of A. akallopisos was then studied under light intensities of 4.16 x 10¹⁵ quanta.sec⁻¹.cm⁻², 8.85 x 10¹⁵ quanta.sec⁻¹.cm⁻² and this intensity plus natural light. Spawning occurred mainly under 8.85 x 10¹⁵ quanta.sec⁻¹.cm⁻². Fish maintained under this light intensity exhibited significantly more of nest cleaning behaviour in terms of frequency and duration than fish maintained under low light intensity. A minimum light intensity of 8.85 x 10¹⁵ quanta. sec⁻¹.cm⁻² is recommended for conditioning of this species. This study can be of practical relevance to hatchery managers who can use the methods developed and record predictors for spawning in A. akallopisos and other Amphiprion species. In this way imminence of spawning may be estimated. Most importantly, the study also has academic merit as little work has been undertaken in this field. Although the observational method used in this study was adequate for the purposes of the investigation, future work of this nature should incorporate other methods of documenting gonadal development such as gonadal staging and GSI in order to obtain more conclusive results.
Full Text:
Date Issued: 1998

Apparent digestibility coefficients of feed ingredients and essential amino acid requirements of dusky kob (Argyrosomus japonicus)

Authors: Adesola, Abidemi Adejoke
Date: 2017
Subjects: Amino acids in animal nutrition , Fishes -- Feeding and feeds , Argyrosomus japonicus , Argyrosomus , Argyrosomus japonicus -- Nutrition , Argyrosomus -- Nutrition , Argyrosomus japonicus -- Feeding and feeds , Argyrosomus -- Feeding and feeds
Language: English
Type: Thesis , Doctoral , PhD
Identifier: http://hdl.handle.net/10962/32140 , vital:24014
Description: Important to the evaluation of potential feed ingredients for inclusion in fish diets should be their digestibility and amino acid requirement so that feeds can be formulated on a digestible basis rather than a gross nutrient basis. This thesis established techniques for faecal collection, the validity of digestibility markers, it determined apparent digestibility coefficients for various novel feed ingredients, and it established the optimal lysine requirement for Argyrosomus japonicus, which was used to estimate each of the essential amino acid requirements by using the ideal protein concept. There were no significant differences in dry matter apparent digestibility coefficients when faeces were collected by stripping (77.0 %), dissection (80.1 %) or settlement (83.5 %). Faecal collection by the settlement method produced the most reliable digestibility data. Apparent digestibility coefficients for dry matter, crude protein and energy calculated using acid-insoluble ash were higher (84.0 %, 93.2 % and 93.0 %, respectively) than those using chromic oxide (55.7 %, 79.1 % and 78.2 %) and titanium dioxide (58.6 %, 79.7 % and 80.5 %). The magnitude of variation in digestibility coefficients obtained using acid-insoluble ash was always lower than that obtained with the other markers. Therefore, acid-insoluble ash was preferred as a dietary marker. Using the above protocol, protein and amino acid digestibility of some animal and plant protein ingredients were evaluated in a series of experiments. The first trial compared the apparent digestibility coefficients of some animal products included as single protein source in the test diets. Apparent protein digestibility values were 84.5 %, 83.8 %, 85.8 % and 83.1 % for fishmeal-prime, fishmeal-standard, poultry meal and pork meal, respectively. Apparent digestibility coefficients for poultry meal were comparable to those of fishmeal, which indicate its potential as a substitute for fishmeal in the diets of A. japonicus. The second trial determined the apparent coefficients of plant and animal protein sources included at 30 % into a practical reference diet (70 %). Apparent protein digestibility ranged from 92.4 % in sunflower meal to 85.5 % in corn gluten meal. Soybean meal is a promising feed ingredient in A. japonicus due to the high apparent digestibility of its protein (92.0 %) and essential amino acid digestibility (mean average 91.4 %). A fundamental assumption in fish feed formulation is that the digestibility of nutrients is additive, i.e., digestibility of a nutrient in one ingredient does not interact with the digestibility of the same nutrient in another ingredient. In the third trial, additivity of feed ingredients was tested using pork meal and poultry meal. The results indicate that the apparent digestibility coefficient of animal protein ingredients could be calculated from compound diets to accurately determine protein and amino acid digestibility in A. japonicus, and possibly other carnivorous fish species. Dietary essential amino acid requirements were determined for juvenile A. japonicus in two trials. A dose-response study was conducted using crystalline lysine to determine the optimal requirement of dietary lysine for A. japonicus. Optimal dietary lysine was estimated at 31.7 g kg-¹ dry diet, corresponding to 73.5 g kg-¹ of dietary protein, based on specific growth rate and broken-line segmented regression analyses. Dietary requirements for other essential amino acids ranged from 22 g kg-¹ (histidine) to 71 g kg-¹ (leucine) crude protein. The results of the present study provided a research tool that could be used to assess and verify the conclusions of earlier dietary work on A. japonicus and in further studies to develop least cost diet formulations for this species. The study also adds to the knowledge of the nutritional requirements of A. japonicus by providing information on the digestibility of plants and animal protein ingredients. It also contributes to future dietary research for this species because this study determines, for the first time, the most suitable methods for investigating the digestibility of raw materials for A. japonicus.
Full Text:
Date Issued: 2017

The use of treated brewery effluent as a water and nutrient source in crop irrigation

Authors: Taylor, Richard Peter
Date: 2016
Language: English
Type: Thesis , Masters , MSc
Identifier: vital:5390 , http://hdl.handle.net/10962/d1021265
Description: Brewery effluent (BE) needs to be treated before it can be released into the environment, reused or used in down-stream activities. Current technologies used to address this concern at the experimental wastewater treatment plant at Ibahyi Brewery (SAB Ltd) include anaerobic digestion (AD), primary facultative ponds (PFP), high rate algal ponds (HRAP) and constructed wetlands (CW). The aim of this work was to determine if BE treated in these systems might be suitable for crop irrigation. A test crop, cabbage (Brassica oleracea cv. Star 3301), grew best on post-AD and post-PFP BE compared to those irrigated with post-HRAP or post-CW effluent. However, the yield was 13% lower than cabbage plants irrigated with a commercial nutrient solution and fresh water. The relatively high conductivity (3019.05 ± 48.72 μs/cm2) of BE may be the main factor reducing the cabbage yields. Post-HRAP and post-CW BE were the least suitable for irrigated crop production due to the higher conductivity and lower nutrient content of these treated effluents. After three months, soils irrigated with post-AD and post-PFP BE had a significantly higher sodium content and sodium adsorption ratio (3919 ± 94.77 mg/kg & 8.18 ± 0.17) than soil irrigated with a commercial nutrient solution (920.58 ± 27.46 mg/kg & 2.20 ± 0.05; p<0.05). However, this was not accompanied by a deterioration in the soil’s hydro-physical properties, nor a change in the metabolic community structure of the soil (p>0.05). After prolonged irrigation with treated BE, sodium is likely to build up in the soil and this can be expected to be accompanied by a deterioration in the soil physical structure. However, crops species such as millet (Echinochloa esculenta), lucerne (Medicago sativa) and saltbush (Atriplex nummularia) reduced the build-up of sodium in the soil. The results suggest that sodium was mainly removed from the soil through plant-assisted leaching. Of the crops grown, lucerne showed the most promise because it improved the soil physical properties, is able to grow well in alkaline environments, is a popular fodder crop and can be harvested multiple times from a single stand. Brewery effluent is more suitable for soil production systems than hydroponic production systems because the soil was able to act as a buffer against the high pH of post-AD BE, whereas in a hydroponics systems the high pH reduced the availability of key minerals to plants. In conclusion brewery effluent contains sufficient plants nutrients to support the growth of cabbages, saltbush, lucerne and millet. However the sodium content of BE is a concern as it accumulates in the soil, and in the long-term it may lead to soil degradation. It is suggested that the brewery change the pH neutralising treatment of BE from sodium hydroxide to potassium hydroxide, or dolomitic lime (calcium and magnesium carbonate) because this would reduce the introduction of sodium into the system, and would increase the suitability of BE for crop production, given potassium and calcium are plant nutrients. The benefits of developing this nutrient and water resource could contribute to cost-reductions at the brewery, more efficient water, nutrient and energy management, create job opportunities with the potential of improving food security in the local community.
Full Text:
Date Issued: 2016

Showing items 1 - 20 of 335

Effect of adding a probiotic to an aquaponic system on plant and fish growth, water quality, and microbial diversity

Movement patterns, stock delineation and conservation of an overexploited fishery species, Lithognathus Lithognathus (Pisces: Sparidae)

Early stage ichthyofauna from shallow water habitats of the Angola-Benguela frontal zone

The growth characteristics of sparid otoliths

An assessment of the monkfish resource of Namibia

Regional connectivity, differentiation and biogeography of three species of the genus Lutjanus in the western Indian Ocean

A study of the population dynamics, production and potential yield of the sardine Limnothrissa Miodon (Boulenger) in Lake Kariba

Bioaccumulation and histopathology of copper in Oreochromis mossambicus

An ecological study of territoriality in four Cichlid species resident on rocky shores near Monkey Bay, Lake Malawi

Mesopredator release and the effectiveness of camera traps for estimating mammal abundances in the Eastern Cape, South Africa

Distribution, habitat associations and conservation of the Eastern Cape rocky Sandelia bainsii (Perciform: Anabantidae) in the Great Fish River system

Towards understanding the effect of size variation on the aggressive and feeding behaviours of juvenile dusky kob Argyrosomus japonicus (Pisces: Sciaenidae)

The role of microhabitats within mangroves: an invertebrate and fish larval perspective

Biology, population dynamics and management of carpenter (Argyrozona argyrozona) an endemic South African reef fish

A nutritional evaluation of effluent grown algae and zooplakton as feed ingredients for Xiphohorous helleri, Poecilia reticulata and Poecilia velifera (Pisces : Poeciliidae)

Towards a new approach for coastal governance with an assessment of the Plettenberg Bay shore-based linefishery

Understanding biotic interactions in invaded pond communities in the Sundays River irrigation network, South Africa

Reproductive behaviour of the skunk clownfish, Amphiprion akallopisos, under captive conditions

Apparent digestibility coefficients of feed ingredients and essential amino acid requirements of dusky kob (Argyrosomus japonicus)

The use of treated brewery effluent as a water and nutrient source in crop irrigation