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.

Thesis (Ph. D. (Ichthyology))--Rhodes University, 2002.

The importance of fish culture has been increasing since 1990’s. The steady growth of fish culture helps to ensure a stable supply of fish for human consumption. However, when compared with capture fisheries, production from fish culture is greatly influenced by fish diseases. Outbreaks of fish diseases have caused great economic loss to fish culture. Research has been conducted to understand and reduce the occurrence of fish diseases in fish culture. In Hong Kong, bacterial infection is the most common cause of fish diseases. This project is therefore directed to isolate and identify the causative bacterial pathogen of some fish disease cases with the aim of setting up a local fish disease database for assisting the identification of diseases and improving the understanding of fish diseases in fish farms in Hong Kong. In this project, seven fish disease cases caused by bacteria were investigated with the AFCD officials in Hong Kong. Nine fish disease bacterial pathogens were isolated and identified using different methods (including commercial biochemical test kits, automated system and DNA sequencing). The bacteria identified included Aeromonas hydrophila, Lactococcus garvieae, Streptococcus agalactiae, Streptococcus dysgalactiae, Streptococcus iniae, Vibrio vulnificus and Aeromonas salmonicida. Sensitivity tests to 10 common antibiotics conducted for the identified bacteria showed that spectinomycin is the most broad spectrum antibiotics. In addition, a long-term physical storage of bacterial stock with glycerol and glass beads was established for further research of the identified bacteria. For efficient data analysis, an electronic database using Microsoft Access to hold the identification results and case history of each isolated bacteria was developed. Different data entry forms and reports were also constructed to facilitate easy data entry and data access for users. The three bacteria identification methods were compared for their efficiency and accuracy. Some limitations encountered in this project including time constraints and low accuracy of some biochemical identification tests were discussed and recommendations to overcome these limitations and improvements to the constructed database were made. / published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

The richness of nervous systems represented by extant fishes has not yet been determined; the brain morphology of many species, indeed, many groups, remain undescribed. For this reason we have examined esociform teleosts and focused on three goals: 1) to provide the first basic descriptions of the brains of two esociform teleosts, Esox masquinongy (muskellunge) and Esox lucius (northern pike); 2) to describe the development of E. masquinongy brains; and 3) to compare the neuronal features between E. masquinongy and E. lucius in light of the ontogenic pattern of E. masquinongy. We demonstrate that a suite of differences exists between the brains of these two congeners. Relative to the brains of E. lucius, the brains of E. masquinongy exhibit a number of paedomorphic features. This heterochronic shift parallels the differences in non-neuralmorphological features previously described between these two species. We identify three features that cannot be explained by this heterochronic shift: 1) the optic nerves of E. masquinongy and E. lucius cross oppositely, E. masquinongy have optic nerves that cross left nerve dorsal, E. lucius cross right nerve dorsal; 2) Esox lucius have a consistent cellular discontinuity in the telencephalon between Dm, and Dd that is not present in E. masquinongy; and 3) adult E. lucius retain a neural canal opening that closes in larval E. masquinongy, a peramorphic exception to the paedomorphic pattern. / Department of Physiology and Health Science

Typescript. / Bibliography: leaves 212-226. / Photocopy. / xv, 226 leaves, bound ill. 29 cm

Thesis--City University of New York. / Bibliography: p. 327-340.

Thesis (M.S.)--Texas A & M University, 2003. / "December 2003." Includes bibliographical references (p. 56-64).

Thesis (Ph. D.)--University of Chicago, Department of Organismal Biology and Anatomy, August 2000. / Includes bibliographical references. Also available on the Internet.

Thesis(PH.D.) - Carleton University, 1973. / Also available in electronic format on the Internet.

In Malawi, fish contribute about 60-80% to the country's animal protein supply. The greater proportion (> 50%) comes from Lake Malawi. Bathyclarias nyasensis and other clariid catfish contribute up to > 20% of the total catches. Catches of Bathyclarias nyasensis in the inshore area of the south-east arm of Lake Malawi are declining and a management plan for the fishery is essentially lacking. There is paucity of biological data that precludes the use of any option to manage the species. The principal aim of the thesis was to define the ecological role B. nyasensis, the most abundant and common of the Bathyclarias species. By examining life history characteristics within a food web context, it was hypothesized that the study would provide an insight into the interrelationships between species, and, hence form the basis for the development of a rational exploitation strategy for the species. The study was undertaken in the south-east arm of Lake Malawi (9° 30'S, 14° 30'S). The principal objectives of the study were to investigate the feeding ecology of B. nyasensis by examining morphological characters and structures associated with feeding, diet of B. nyasensis, food assimilated in the species using carbon (∂¹³C) isotope analysis, daily food consumption rate for B. nyasensis; and to relate the feeding ecology to life history traits such as age, growth, and some aspects of the reproductive biology of B. nyasensis. The suitability of sectioned pectoral spines and sagittal otoliths to age B. nyasensis was assessed. Due to reabsorption of growth zones with increasing spine lumen diameter with fish size, and the relatively low number of spines that could be aged reliably, only otoliths were used. The maximum age for B. nyasensis was estimated at 14 vears. Growth was best was described by the four parameter Schnute mc: lt ={42+(81¹·⁸ - 42¹·⁸)x1-e⁻°·°⁵⁽t⁻¹⁾}¹/¹·⁸ over 1-e⁻⁽⁻°·°⁵⁾⁽¹¹⁾ for female, lt={41+(98¹·² - 41¹·²)x 1-e⁻°·°²⁽t⁻¹⁾}¹/¹·² over 1-e⁻⁽⁻°·°²⁾⁽¹³⁾ and for male fish. Age-at-50% maturity for females and males were estimated at 7 years and 4 years, respectively. Typically, fish grew rapidly in the first year, but slower during subsequent years. Smaller fish were found inshore while larger fish were found in offshore regions. It was hypothesised that the rapid growth in the first year and slower growth later is a consequence of change in diet from high quality and abundant food source to a more dilute food and that this may be associated with a shift in habitat. Morphological characters associated with feeding were used to predict the food and feeding behaviour of B. nyasensis. The size of premaxillary, vomerine, pharyngeal dental and palatine teeth and premaxillary and vomerine tooth plates suggested the capability of B. nyasensis to handle both large and small prey, with a propensity towards smaller prey in composition to C. gariepinus. The molariform teeth on the vomerine tooth plate suggested that molluscs form part of the diet. The relative gut length (1.27±0.24) suggested omnivory, with an ability to switch between planktivory and piscivory. Buccal cavity volume and filtering area changed with fish size at 500-600 mm TL upon which it was hypothesised that the fish diet changed to planktivory at this size. Detailed diet analysis provided information upon which the above hypotheses could be accepted. Percent Index of Relative Importance (%IRI) and a multi-way contingency table analysis based on log-linear models were used to analyse diet data. Results showed that B. nyasensis is omnivorous, but with a distinct ontogenetic dietary shift from piscivory to zooplanktivory at 500 - 600 mm TL. The increased buccal cavity volume at the same fish size therefore, suggests that B. nyasensis is well adapted to filter the dilute zooplankton resource. Increased foraging costs of feeding on zooplankton explained the slower growth of larger fish. The dietary shift was finally corroborated by results of the ∂¹³C isotope analysis. A polynomial equation described the change in carbon ratios with fish size: ∂¹³C = - 33.188 + 0.4997L - 0.0045 (total length)² (r² = 0.598, n = 12, p=0.022). The ontogenetic shift in diet was synchronised with a habitat shift postulated in life history studies. In the inshore region, B. nyasensis were predominantly piscivorous (apex predators), and were zooplanktivorous in the offshore region, thereby forming part of the pelagic food web in the latter region. After examining "bottom-up" and trophic cascade theories, it was postulated that perturbations of the B. nyasensis stock would be discernible both at the top and lower trophic levels. As a piscivore and therefore apex predator, effects of overfishing B. nyasensis in the inshore region could cascade to unpredictable ecological changes in inshore areas and, due to the ontogenetic habitat shift, in the offshore regions. Examples of trophic cascade phenomena are provided. On the basis of the feeding study, it was possible to reconstruct the pelagic food web of Lake Malawi. Apart from the lakefly Chaoborus edulis, B. nyasensis is the other predator that preys heavily on zooplankton in the pelagic zone. Perturbations of the B. nyasensis stock could affect size composition of zooplankton which in tum, could affect production of C. edulis, a resource for the top predators in the food web. The findings of the present study contributed to the ongoing debate of introducing a zooplanktivore into the pelagic zone of Lake Malawi. Proponents for the introductions have argued that zooplankton predation by fish is inferior to that of C. edulis. Introduction of a clupeid zooplankton was proposed as a strategy to boost fish production in the lake. The zooplanktivore would either out-compete or prey on C. edulis to extinction. Opponents to this view argued that zooplankton biomass in the pelagic region was too low to support introductions and that the fish biomass in the pelagic region may have been underestimated. Results from the present study suggest that planktivorous fish (including B. nyasensis) might not be inferior to C. edulis in utilising the zooplankton resource; B. nyasensis is well adapted to utilise the dilute zooplankton resource, and by omitting B. nyasensis from previous studies, overall zooplankton predation by fish may have been underestimated by between 7 - 33%. On the basis of the theoretical migratory life history cycle of B. nyasensis, it is recommended that the current interest in increasing fishing effort in offshore areas should proceed with caution. Ecological changes that may have occurred in the inshore areas due to overfishing have probably not been noticed: as the offshore zone has never been fished. The latter zone may have acted as a stock refuge area. Higher fishing intensity in the offshore areas could lead to serious ecological imbalances and instability. The study has shown that life history characteristics studied in the context of the food web, and in the absence of other fisheries information and/or data, strongly advocates the precautionary principle to managing changes in exploitation patterns.