Two possible ways in which fish may acclimate to prolonged exposure· to sublethal levels of endosulfan were investigated: induction of the hepatic monooxygenase system and changes in haematology. These studies also involved an examination of the ultrastructure of liver and gill tissue. Endosulfan caused none of the characteristic phenobarbital-type inductive effects on the liver of Oreochromis mossambicus. There was no increase in cytochrome P-450 levels, microsomal protein or hepatosomatic index. The reasons for the lack of induction are discussed. The effect of endosulfan on the following haematological parameters was determined: haemoglobin, erythrocyte count, microhaematocrit, mean erythrocyte volume and mean erythrocyte haemoglobin concentration. The only effect was an increase in erythrocyte count. The value of changes in haematological parameters as indicators of pollutioninduced anemia in the field is discussed. No changes in gill ultrastructure were noted although electron micrographs of liver tissue showed lesions in hepatocytes. The diagnostic value of pollution-induced pathological changes on cell ultrastructure are discussed. Recommendations are made with regard to future large scale application of pesticides on or near large water bodies

More than twenty years ago, over twenty species of the rock-dwelling cichlid species (Mbuna) were translocated from the northern Lake Malawi, where they are endemic, to Thumbi West Island, Lake Malawi National Park, in the southern part of Lake Malawi. Among these species, Cynotilapia afra, Pseudotropheus callainos and Pseudotropheus tropheops 'red cheek' are strongly territorial, and have increased substantially in number and are widely distributed, particularly in the three to seven metre depth band of the rocky habitats at the Island of Thumbi West. It is feared that the increase in population density of translocated species (hereafter referred to as introduced species) may be at the expense of ecologically equivalent native species which could be eliminated. In this thesis the following key hypotheses have been tested: (i) that the introduced species having originated from a region of Lake Malawi which is generally poor in nutrients and introduced in an area which is richer in nutrients, would cope better than the native species during periods of nutrient scarcity which occur frequently, often seasonally in oligotrophic lakes, such as Lake Malawi; (ii) that the introduced species are fitter than their ecologically equivalent native species in the acquisition of territorial space in which they breed, feed and seek shelter, and (iii) that introduced and native species coexist by utilizing different microhabitats. Results show that: 1. the introduced species, P. callainos and P. tropheops 'red cheek' may have responded positively to enhanced nutrient availability, as they were found to have better condition factors and fecundity indices at Thumbi West Island than at sites of their origin, in the northern lake Malawi. Cynotilapia afra, P. callainos and P. tropheops 'red cheek' also maximise their life-span fecundity by starting to reproduce at relatively smaller size than the native species with which they overlap in microhabitat requirements. Similarly, their breeding peaks precede the breeding peaks of the native species with which they overlap in microhabitat requirements. Consequently, due to priority residence effects, the offspring of introduced species may have a competitive edge in the use of essential resources, e.g., refuge over the offspring of the native species whose peak-recruitment occurs later in the year. 2. There is an overlap between the introduced and native species in their microhabitat requirements. Consequently, interference competition between them for territorial sites occurs. The choice of optimal territory sites is constrained by the fact that females preferentially mate with males that defend significantly smaller holes, or crevices among the rocks, probably as a means of minimizing egg predation during spawning. 3. The population of territorial males of introduced species seems to grow exponentially, depending on the availability of suitable microhabitats, and an equilibrium between them and males of the native species may be reached. Competition for optimal territory sites seems to intensify, once the carrying capacity in a particular area has been reached, and it is at this stage that some territorial males of the introduced and native species with similar microhabitat requirements, e.g., C. afra and P. zebra, or P. tropheops 'red cheek' and its sibling native species, P. tropheops 'orange chest' displace each other. However, it seems unlikely that any of the native species which were compared with the introduced species would be driven to extinction because: (a) there is a considerable interspecific territory turn-over between the introduced and native species that overlap in microhabitat requirements. (b) Even in situations where some of the native species occur in microhabitats that are not of their preference, they occupy patches of suitable sites and are capable of breeding. (c) It has been suggested that since introduced and native species breed throughout the year and are polygamous and have intraspecifically shared paternity, they are capable of fertilizing many gravid females of their own species. Therefore, the population of native species may not be detrimentally limited by the presence of introduced species. (d) The introduced and native Mbuna species that prefer small rocks coexist in the same microhabitats, partly by feeding at different sites with different intensity and they also feed at different heights in the water column. 4. The following studies have been recommended before any management intervention, such as culling is adopted: (i). interaction between the introduced and native species in the shallow and deep rocky habitats; (ii) space utilization and survivorship of juveniles of the introduced and native species; (iii) laboratory studies to confirm the role of different nutrient regimes on the fecundity of Mbuna; (iv) the possibility of hybridization between the introduced and native species; (v) monitoring of population growth and distribution of the introduced species around Thumbi West Island should continue in order to detect their long-term effects on the native species.

The effect of impoundment size on fish has been investigated. Investigators have reported that greatest growth has taken place in large in some instances and in small impoundments in others. The effect of varying space on the cichlid Aequidens pulcher Gill, was examined in four tanks of equal volume. Each tank was divided into two replicates in the compartment ratios 9:3:1 and each contained 90:30:10 fish respectively. A higher density tank had twice the fish number in all compartments and had lowest growth due to either reduced oxygen availability, increased biomass, increase in activity or stress due to small nearest neighbour distances. Fish in a tank with mirrors on all compartment walls had a reduced growth possibly due to visual stress compared to a control lacking mirrors. A further tank had twice the surface area of the control, a greater distance between nearest neighbours and greatest fish growth. Growth was significantly greater, at the 95 percent confidence limit, in all small compartments of tanks and activity was significantly greater in large compartments. In an identical treatment design to that of the control fish were shown to lose weight while being starved. The fish in the larger compartments were more active and lost most weight. A strong suggestion that the lower growth rate in large compartments was due to greater activity, possibly this was related to the total available swimming space per fish. Fish aggression was greatest in small compartments and decreased over time, possibly as a result of conditioning. / Science, Faculty of / Zoology, Department of / Graduate

No description available.

Observations of habitats are reported. A series of underwater experiments were conducted in natural habitats to answer questions concerning a) why Lamprologus ocellatus and Lamprologus ornatipinnis bury gastropod shells refuges into the substrate, and b) to examine interspecies differences in shell-using behaviours. Some behaviour patterns were analysed using phylogenetic methods. Lamprologus ocellatus and L. ornatipinnis responded to new shells in a variety of ways, shells were moved, buried (and used) or hidden (buried and not used). How shells are utilised seems to be dependant on a complex of factors such as the size and quality of new the shell and the number already in the territory. Shell use may also be affected by neighbour species, sex, size and predation levels. There are interspecific differences in the size of shells used and the methods of shell use. The latter results in species-characteristic shell orientations, vertical burial in L. ocellatus and horizontal burial in L. ornatipinnis. Shell orientation does affect other species/use of shells. Shell movement and vertical orientation appear to be apomorphic while shell hiding and burial are pleisiomorphic within the genus Lamprologus. Numerous cues are involved in stimulating shell burial. Most of these cues are actively sought by the fish by external and internal inspections. Shell burial therefore appears to be a method of reducing the information gathering ability of potential shell-dwelling competitors. Shell burial can therefore be regarded as an investment process which enhances the residents ability to defend its territory. Males can also control the distribution of open shells within teritories and thus control mate access to shells. This behaviour could be a significant factor in the evolution of marked sexual dichromatism exhibited within the genus.

The cichlid fish Pseudocrenilabrus philander is widely distributed in southern Africa. Many of the populations occur in small, insular, geographically isolated water bodies, some of which are in arid areas. These small allopatric populations have been isolated for thousands of years and gene flow between them is non-existent or severely restricted. Populations were found to be different in terms of coloration, size of individuals, sexual dimorphism and behaviour. This thesis involved the determination of the taxonomic status of these isolated populations, from a morphological point of view. This has been part of a larger project, involving genetic and behavioural studies, to determine whether the different populations are geographic races of a single species, or whether they are species. Heritability of the observed differences was tested by breeding through three generations under uniform laboratory conditions. The populations from which wild-caught individuals were drawn could be identified on the basis of colour. There were some differences in anatomy between populations, but none of these were entirely distinctive for a particular population. When bred under laboratory conditions, populations did not show a tendency towards uniformity, as would be expected if morphological differences were environmentally induced. However, there were slight changes in the oral and pharyngeal bone form which may be diet related. Although there are morphological differences between populations and between wild-caught and laboratory-bred populations, it is suggested that the populations of P. philander are not fully differentiated and thus in the stages of incipient speciation. other studies on P. philander have introduced an element of uncertainty in that they show different results. Behavioural work suggests that different populations would behave as different species if they were to become sympatric. Karyological and mitochondrial studies showed that there were no differences between populations. Protein electrophoresis showed that populations were genetically unique. Since the various species and subspecies of Pseudocrenilabrus have been based on morphological criteria, the approach and conclusions in this study are based entirely on morphological criteria. These studies have practical implications for conservation, as some of the small populations are threatened with extinction. If the differences between the populations were ecophenotypic (i.e. related to their environment), then threats to some populations would not affect the conservation status of the species as a whole. If, however, such differences were genetic (i.e. the populations have evolved separately), then the extinction of small, isolated populations could mean the loss of actual species. This study strongly suggests that populations are incipient species and thus should be conserved.

Thesis (Ph. D.)--Illinois State University, 1968. / Title from title page screen, viewed Aug. 18, 2004. Dissertation Committee: Jack A. Ward (chair), John Frehn, Howard R. Hetzel, Robert Weigel, Edwin Willis. Includes bibliographical references (leaves 126-129). Also available in print.

Parasites are an important component of every ecosystem, and their interactions with hosts can directly impact the fitness of the host organisms. Despite their significance, it is still largely unknown which host traits predispose a species to increased risk of parasite attack. In the present study, I investigated host and ecological correlates of parasite load in Lake Tanganyikan cichlids using phylogenetic comparative analyses. Specifically, I tested the effect of body size, brain mass, gut length, depth, trophic level, habitat complexity and mating system on parasite prevalence and diversity.  I found that the variation in both average infracommunity richness and parasite prevalence were partly explained by host body mass and habitat complexity. Total parasite diversity, on the other hand, was significantly related to mating behaviour as well as habitat complexity. The comparative analysis presented here is, to the best of my knowledge, the first to investigate determinants of parasite load in Lake Tanganyikan cichlids. As such, my results support several major hypotheses concerning the factors that underlie parasite prevalence and diversity and have broad implications for our understanding of parasite-host interactions.

Thesis (Ph. D.)--Illinois State University, 1973. / Title from title page screen, viewed Oct. 14, 2004. Dissertation Committee: J.A. Ward (chair), Lauren Brown, D. Birkenholz, B. Richards, J. Tone. Includes bibliographical references (leaves 277-284) and abstract. Also available in print.

The phenotypic plasticity of the cichlid Oreochromis mossambicus was examined in fresh and brackish water populations living in the eastern Cape near the southern extremity of the natural range. The primary goal of the study was to examine the wide variety of life-history styles which were expressed in relation to the varying environmental conditions. Four natural populations were studied during 1986 and 1987, and some experimental work under artificial conditions was carried out at the Rhodes University fishfarm during 1988. This comparative approach gave insights into the complex interactions between biotic and abiotic factors which are exploited by this hardy species. O. mossambicus displayed a wide variety of life-history tactics under harsh environmental conditions. The growth of juvenile fish was rapid and mortality of the young-of-the-year was high. Age at first onset of sexual maturity ranged from one to three years. Under harsh conditions growth rate was markedly reduced after maturity, which occurred during the second or third summer and growth disparity between the sexes was more pronounced. Longevity was found to vary from five to ten years for different populations. Under more favourable conditions (resembling the typical "floodplain" habitats of this species at lower latitudes) very rapid juvenile growth, and a high maximum mass of over 2300 g for both sexes was iii achieved. Sexual maturity under these conditions could be delayed until the third or fourth summer of life. O. mossambicus demonstrated an ability to withstand and even benefit from fluctuating water levels, and adjusted its life style according to the prevailing conditions: at times of high water level recruitment was low and sexual maturity delayed. During low water periods reproductive rates increased. Q. mossambicus showed a distinct preference for gentle gradients and well-vegetated habitats for feeding, nesting and refuge. During the study winter temperatures were near and at some times below the generally accepted lower limits for this species. This implies that these indigenous populations have a degree of cold tolerance. A further implication is that Q. mossambicus has the ability to thrive under adverse conditions which may partially explain its wide and successful colonisation of water bodies far from its natural range, and its obvious fisheries potential.