Göttingen, Phil. Diss. v. 4. Juli 1934.

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.

M.Sc. (Zoology) / This study was undertaken to determine the osmotic regulation of Labeo capensis and to investigate the effectiveness of the addition of salt to water in which the fish are transported. The blood of L. capensis in tap water has a lower pH value than that of the same species acclimatized to salt water. It seems that the pH of fish transported in salt water is not altered immediately as in the case of fish transported in fresh water. In both groups the lowest pH values were reached two days after the fish had been transported ...

Thesis (M. Sc. (Zoology)) -- University of Limpopo, 2012 / The Olifants River System is one of the most polluted river systems in Southern Africa. The Olifants River catchment is characterized by large-scale mining, power generation, heavy industry and inadequate domestic sewage treatment. Fish and crocodile kills have become commonplace over the past decade, especially in the upper catchment and Kruger National Park. The present study was carried out at Loskop and Flag Boshielo dams, two major impoundments in the Olifants River. Water and sediment samples were collected at each dam during winter (July 2011) and summer (November 2011), frozen and sent to an accredited water lab for chemical analysis. Atleast fifteen fish specimens from each dam were collected during each survey using gill nets. To evaluate the health of red-nose labeo, (Labeo rosae) in the two dams, fish organs were assessed macroscopically using the fish Health Assessment Index (HAI) protocol and a section of liver tissue and gills were dissected out, frozen and sent to an accredited water lab for metal analysis. The remainder liver samples were fixed in 10% buffered formalin and sent to University of Pretoria Pathology Laboratory for histopathological analysis. The concentration of nutrients and ions were higher at Loskop Dam whereas most metal concentrations were found to be higher at Flag Boshielo Dam. The present study categorised Flag Boshielo Dam as oligotrophic with Loskop Dam being mesotrophic. The concentration of aluminium, copper, antimony, iron, lead, selenium and strontium was higher at Flag Boshielo Dam with manganese, silica and zinc being higher at Loskop Dam. Although the concentrations of these toxic constituents varied, there were no significant differences between localities (p>0.05). The constituents that showed high concentrations in sediment were iron and aluminium. The general trend of accumulation in sediment was as follows: Fe > Al > Si > Mn > Zn > Cu > Sb > Sr > Pb > Se at Loskop Dam whereas at Flag Boshielo Dam was as follows: Fe > Al > Mn > Si > Zn > Cu > Sr > Pb > Sb > Se. The liver generally accumulated higher concentrations of metals than the other tissue. General trend of liver > gills > muscle was reported for Al, Cu, Fe, Pb, Sb, Se, Si and Zn with gills > liver > muscle trend being reported for Mn and Sr at both localities. Macroscopic abnormalities were observed for some gills and liver at both localities. Parasite (Lernaea cyprinacea) induced lesions on the skin and mild erosion on the tail fin of some fish were recorded at Flag Boshielo Dam. Most of the histopathological alterations were common at both localities but hydropic glycogen and hyaline droplets were observed only at Loskop Dam, with haemosiderin being observed at Flag Boshielo Dam. Both quantitative HAI results and histopathology have shown that the fish population from Flag Boshielo Dam are in better condition/health than the population Abstract Abstract Page iv from Loskop Dam. There might be a correlation between the nutrient levels and fish health. The overall ecological state is better at Flag Boshielo Dam than Loskop Dam.

Thesis (Ph. D. (Ichthyology & Fisheries Science))--Rhodes University, 2004.

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

M.Sc. (Zoology) / Please refer to full text to view abstract

M.Sc. / Metal ions have become an increasing source of pollution in the natural waters of South Africa. This phenomenon is related to the rapid industrial, mining and agricultural activity growth along rivers, especially in the Upper catchment of the Olifants River, Mpumalanga. In general, metal ions have - negative effects on the physiology of fish and other aquatic biota in metal polluted waters. In this study. the sublethal effects of, manganese were determined by exposing the freshwater fish, Oreochromis mossambicus, to this metal in an experimental flow-through system. The exposure times were divided in acute (96 hours) and chronic (26 days) exposures, both at 23 ± 1°C. The results obtained showed changes in the general, haematological, metabolic, osmoregulatory variables, as well as the differential white blood cell counts. These changes indicated several effects in the physiology of a mossainblais after sublethal manganese exposure. Significant differences (P < 0.05) were found between the haematological variables of the control and exposed fish. During chronic exposure, an oxygen deficiency developed due to , the epithelial lifting of gill lamellae. As a result of hypoxia the red blood cell numbers, haemoglobin-, haematocrit and lactate concentrations increased to uplift the depleted oxygen situation. The significant differences (P < 0.05) found in the sodium, potassium,. calcium and chloride concentrations are mainly as a result of gill damage. Manganese showed a disruptive influence on the structural organization of the gill. The differential white blood cell counts performed , showed significant fluctuations. This leucocytosis and leucopenia are normal reactions of the fishes’ body against infections of foreign substances, such as metal ions. It was concluded that the general haematology, metabolism, osmoregulation and differential white blood cell counts can, be used as indicators in detecting the effects of sublethal manganese exposure on fish.

M.Sc. (Zoology) / Temperature plays a very important role in the metabolic environment of coldblooded animals such as fish. The primary objective of this study was to evaluate the quality of digestive processes and the importance of temperature in the digestive system of Labeo capensis. An important consideration in the choice of the experimental animal was the economic potential and widespread occurrence of Labeo capensis in the riversystems of the Transvaal. The experimental animals were kept at three different acclimation temperatures ( 14, 19 and 25 + 1°C) for a period of six weeks. An assessment of the influence of acclimation temperature on enzyme activity vas made using test kits supplied by BOERINGER-MANNHEIM. No information exists on the morphohistology of Labeo capensis and therefore investigation on the anatomy of the digestive system was carried out in this survey. The ventro-anterior mouth is ideally situated for bottom-feeding. Pharyngeal teeth and a pharyngeal pad (or palatal organ) is situated dorsally at the entrance to the oesophagus. A short oesophagus, which possesses both a supra- and infraoesophageal valve, exists. No stomach is present and the intestinal bulge affixes the intestine to the oesophagus. The exceptionally Iona intestinum proper lies coiled in the abdominal cavity. No rectum can be identified. The micro-anatomy of the intestinal proper and bulge differs minimally. The intestinal bulge possesses longer, slimmer villi in comparrison of the flat thickened villi of the intestine proper. The bulge lacks a longitudinal muscle layer. L. capensis cellulase and dicarrboxylase activty may be contributed to the intestinal microflora and/or foodstuffs present in the digestive system. Amylase possesses the highest and the proteases (trypsin and chymotrypsin) the lowest activity. The effect of acclimation temperature is most evident on amylase, and to a lesser extent on the phosphatases. Trypsin and chymotrypsin activity is less affected by acclimation temperature, although a distinctive loss of activity is recorded for both these enzymes. The loss of acid phosphatase activity is partially contributed to the rise in intestinal pH. The effect of reaction temperature was measured and recorded as AT-values.

M.Sc. (Zoology) / The Vaal River system is constantly subjected to pollution from various industrial, mining and agricultural activities. Consequently, pressure is continually exerted on the health of its fish communities and it was suspected that this may be a contributing factor to the repeated fish kills that have occurred in various sections of the river over the past few years. The aim of this study was to assess the health status of three fish species that were affected by the most recent mass fish mortality in the Vaal River. This was done using a combination of techniques including a histology-based health assessment (HHA) that involved a standard fish necropsy, the evaluation of blood parameters as well as a microscopic assessment of the liver, kidney, gills, and gonads. The histological results were semi-quantitatively assessed. Selected chemical substances were also tested for in water, sediment and the skeletal muscle tissue of the fish. Clarias gariepinus, Labeo capensis and Labeo umbratus specimens were collected from the Vaal River, approximately 2480m below the Vaal Dam (Latitude 26°51'17.47"S; Longitude 28° 7'16.58"E) following the latest occurrence of a fish kill in November 2011. Fish were collected using gill nets. Water was sampled in triplicate at three locations, and in situ measurements were done for selected physico-chemical parameters. Sediment samples were also collected and subjected to a sequential extraction technique and quantification of the heavy metals was done using Inductively Coupled Plasma-Mass Spectroscopy (ICP-MS). Metals in skeletal muscle tissue and water were quantified using the same technique. An analysis of variance (ANOVA), followed by the appropriate post-hoc test was performed to determine differences between means of variables i.e. morphometric, histological, substance concentration and blood parameters...