D.Sc. / Please refer to full text to view abstract

The biology of three large cyprinid fishes, Barbus holubi, B. kimberleyensis and Labeo capensis, was studied in a large turbid man-made lake on the Orange River, South Africa. The influence of environmental fluctuations on population dynamics was examined in relation to biological adaptations. On this basis inferences were made about the effect exploitation would have on the populations, and management alternatives were considered. Lake Ie Roux is situated in a semi- arid area, downstream from another large reservoir, Lake Verwoerd. In the pristine river, flooding is seasonal, and floodwaters carry a heavy silt load. Lake Verwoerd acts as a silt-trap and changes in turbidity in Lake Ie Roux (Secchi disc readings range from 15 to 160 cm) are influenced by hydrological management and are not necessarily seasonal. Water temperatures in the regulated river connecting the two lakes depend on the pattern of water release, and fluctuations in Iake levels depend on management practices. Reproduction was studied by examination of gonads and from the distribution of newly hatched juveniles. Age and growth was interpreted from the reading of scales and otoliths. Relative year class strength, dispersal and mortality were monitored using catch data from a regular, standardized gillnetting survey. The Barbus species spawn in the regulated river in spring or summer. Spawning is coordinated for a large part of the population and B. holubi spawn four to six weeks earlier than B. kimberleyensis. The juveniles are 'initially found along the shoreline, but later move into the pelagic zone and disperse throughout the lake. Year class strength is dependent on time of spawning and a late spawning results in a poor year class. For this reason, year class strength of B. kimberleyensis is generally poor, but there is a greater variation in year class strength of B. holubi, which is the dominant large Barbus. The two Barbus species exploit the pelagic zone, visually predating on zooplankton. When turbidity increases large scale mortalities occur, especially in B. holubi. Mortalities more than compensate for the reduction in carrying capacity, and the size of the reduced population may be inversely related to initial abundance. Growth rate is similarly affected by turbidity and density, and size at sexual maturity in B. holubi is reduced when growing conditions deteriorate. Labeo capensis do not form a homogenous population in Lake le Roux. Spawning occurs throughout the lake, but is erratic, probably depending on local rainfall. At each locality, more than one spawning may occur during spring and summer because of temporal variation in gonadal development. Juvenile survival appears to be mainly dependent on water level fluctuations, and strong year classes were formed when the lake was filling during the first two years. Subsequent year classes were weak. Subadult and adult B. capensis are herbivorous and depend on autochthonous production for food. They are relatively sedentary, but when turbidity increases fish smaller than 200 mm disperse, probably in response to food shortages. Mortality rates may be accelerated but mortalities are not as high as in B. holubi. The growth rate of B. capensis is variable and depends on turbidity and population density. Size at sexual maturity remained relatively constant during the study period. B. holubi has a relatively fixed reproduction cycle in Lake le Roux and exploitation is likely to dampen fluctuations in population density. Population growth and stability could be further promoted through hydrological management. B. kimberleyensis does not represent an exploitable population in Lake le Roux, although the large size obtained by this species (>3 kg) may be an attraction to anglers. B. capensis does not appear to have the potential to withstand sustained exploitation because of its erratic and generally poor reproductive success. However, the species is long-lived and can sustain relatively high densities under harsh conditions because of its relatively low mortality rates. It was concluded that harvesting of B. holubi must be flexible to promote maximum benefits to commercial and recreational fisheries, but B. capensis which is not an angling species, should chiefly be exploited when catches of B. holubi are poor, but left to recover in between. An alternative management strategy would be to commercially exploit the fish populations of several reservoirs. A monitoring programme could be established to decide when each reservoir is to be exploited to see to the interests of commercial and recreational fishing alike.

No description available.

Ph.D. / Except for agriculture, the mining industry is considered as not only the oldest but also the most important industry. Mining involves the removal of minerals from the earth's crust for usage by mankind. The disturbance during mining activities such as mining effluent has an effect on the natural aquatic environment. In any freshwater environment, the macroinvertebrates form a vital link between the abiotic envinronment and the organisms in higher trophic levels. It is thus true that specific environmental contaminants, such as mining effluent, may directly affect the survival of macorinvertebrates. The density and diversity of macroinvertebrates is in a direct relation with the water quality. For the purpose of this study, attention was given to the effects of gold and coal mine effluent on the macroinvertebrate fauna, as well as to the determination of metal accumulation from the water through the macroinvertabrates to fish. At Case Study Mine One, with an open water system, acidic conditions of the water caused a reduction in the number and diversity of macroinvertebrates. A closed water system, characteristic of Case Study Mine Two, presented a slightly more abudandant macroinvertebrate population than with the previous mine. The results lead one to conclude that the surface water in this study area is of a better quality. Case Study Mine Three had a complex water circuit and presented a greater number and diversity of macroinvertebrates, with the best water quality of the three mines investigated.

M.Sc. (Zoology) / A literature survey revealed gaps in the knowledge on Ergasilus in Africa. This studied aimed to elucidate on some of these matters. Ergasilus sarsi was collected from Lamprichthys tanganicanus during an expedition to Lake Tanganyika in March 2010. The gills of the fish were removed and preserved for further studies. Preserved specimens were studied with dissection- and light microscopy. Some specimens were also studied with a scanning electron microscope (SEM). For light microscopy the specimens were sectioned and then stained with AZAN and H&E. A total of 32 Lamprichthys tanganicanus were collected and studied for ergasilids. The prevalence was 86.40%, the mean intensity 7.56 and the mean abundance 6.38. A total of 204 parasites were collected and only 27 hosts were infected. The highest intensity was 29 parasites. Pearson’s Chi-squared test was used to compare attachment preferences of Ergasilus sarsi. The parasite exhibited site selection but not host specificity. It was noticed that E. sarsi mostly attach to the tip of the gill filament of the second gill arch. The second gill arch receives the largest portion of water flow supporting distribution of newly hatch ergasilid nauplius. There was no significant preference for the dorsal, medial and ventral attachment sites (p-value = 0.000542). However, significant preference between distal, central and proximal regions (p-value = 1.19) was observed. Fryer (1965) observed that the pathology caused by ergasilids is related to their attachment position on the host. Ergasilids display variation regarding morphology of their second antennae. Some have spines and others elongated antennae that wraps around the entire gill filament. This study shows that Ergasilus sarsi (with no spines on the second antennae) wraps around the gill filament and cause considerable damage to the host. The entire gill filament structure changed due to lamellar fusion and proliferation of mucous – and epithelial cells. Comparison of an infected gill to a healthy gill revealed differences. The compression caused by the second antennae caused some blood vessels to rupture resulting in haemorrhage. The swimming legs of the parasite also cause considerable damage by scraping gill tissue off the host and pushing it towards the mouth parts of the parasite. Mucous cells, gill epithelium and blood cells were observed in the vicinity of the mouth and in the intestine of the parasite. An increase in the number of Rodlet cells and mast cells were also observed on the gills in close proximity to the parasite. Increase in the number of these cells clearly indicate an inflammatory response. This is the first record of Ergasilus sarsi on Lamprichthys tanganicanus. This study also provides the first detailed description of the pathology caused by Ergasilus sarsi as well as the attachment distribution of this parasite.

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (leaves 118-131).

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 2001. / Title from PDF title page (viewed Apr. 2, 2005). Vita. Includes bibliographical references (p. 127-141).

Thesis (M. Phil.)--University of Hong Kong, 1974. / Offset from typescript.

published_or_final_version / Botany / Master / Master of Philosophy

Data on the occurrence of freshwater fishes in Ontario lakes were used to evaluate the scale of the processes that are primarily responsible for shaping their distributions and patterns of diversity. In Chapter 2 it is shown that, regardless of the scale of analysis, the most important factors structuring their distributions are climatic measures of energy, suggesting that species tend to be able to survive heterogeneous conditions falling within large areas encompassing their climatic affinities. In Chapter 3 it is shown that the relationship between species richness and energy (annual potential evapotranspiration) changes according to the scale on which it is measured. The species-energy relationship is weak at the local scale and stronger and steeper at increasing regional scales. This scale dependence is due to the ability of high energy regions to accommodate relatively large numbers of rare or infrequent species, and reflects the regional scale at which species respond to environmental gradients, particularly those related to energy. In Chapter 4 the relationship between local and regional species richness is examined. It is found that mean richness of lakes is linearly related to the species richness of the watersheds in which they reside. Together, the results point to the importance of processes that are regional in scale for shaping species' distributions and patterns of diversity.