published_or_final_version / Zoology / Master / Master of Philosophy

published_or_final_version / Zoology / Doctoral / Doctor of Philosophy

Thesis (Ph. D.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 98-114).

published_or_final_version / abstract / toc / Zoology / Master / Master of Philosophy

published_or_final_version / Zoology / Master / Master of Philosophy

published_or_final_version / Zoology / Master / Master of Philosophy

published_or_final_version / Zoology / Master / Master of Philosophy

Goldfish, an exotic originally from Asia, are frequently released into North American waters, causing unknown impacts on native fauna and flora. In the wild, diet overlap between feral goldfish (Carassius auratus) and native red-spotted newts (Notophthalmus v. viridescens) is high, leading to potential interspecific competition over food. In the laboratory, we manipulated densities of goldfish and red-spotted newts to test competition for benthic food organisms between these unrelated species. / No intraspecific interference was noted for either goldfish or newts at any density. However, as density increased food resources were more rapidly depleted by both species, suggesting scramble competition. Foraging strategies of the species differed. Goldfish shoaled more and abandoned food patches before they were depleted, whereas newts were solitary and exhausted a food patch before moving on to new sites. Both species found more food patches when with heterospecifics than with conspecifics, suggesting interspecific information transfer. In addition, goldfish found more food patches than newts in all trials, indicating scramble competition occurred.

Cell survival in conditions of severe oxygen deprivation depends on a wide variety of biochemical modifications, which result in a large-scale suppression of metabolism, preventing [ATP] from falling to fatally low levels. We investigated whether AMP-activated protein kinase (AMPK) has a role in the coordination of cellular modification during hypoxia, which leads to a regulated state of metabolic suppression in the goldfish (Carassius auratus). Energy charge, AMPK activity, protein and gene expression, as well as the translational capacity and phosphorylation state of a downstream target were measured in goldfish tissues during exposure to hypoxia (-0.3 mg 02/L) for up to 12 h. AMPK activity in the goldfish liver increased by 4-fold at 0.5 h hypoxia and was temporally associated with a —11-fold increase in calculated AMPfree/ATP. No change was observed in total AMPK protein or relative gene expression of identified AMPK isoforms. Changes in AMPK activity were also associated with a decreased rate of protein synthesis and an increase in the phosphorylated form of eukaryotic elongation factor-2 (eEF2; relative to total eEF2). Increases in AMPK activity were not seen in hypoxic goldfish muscle, brain, heart or gill, nor was a significant alteration in cellular energy charge seen in muscle. Still, the present study is the first to show that AMPK activity increases in liver in response to short-term severe hypoxia exposure in a hypoxia-tolerant fish. The decreased rates of protein synthesis, a well known component of metabolic suppression, combined with increased phosphorylation of eEF2, a downstream target of AMPK, potentially implicate the kinase in the cellular effort to suppress metabolism in hypoxia-tolerant species during oxygen deprivation.

This study aimed to better understand the clearance of myelin debris during Wallerian degeneration in the goldfish visual paths. Myelin debris was first examined immunohistochemically in the presence or absence of regenerating axons. From these preliminary experiments it was apparent that the clearance of myelin debris was not affected by regenerating axons and that the debris was removed in a differential pattern along the visual pathway. Specifically, in the distal stump of the nerve as well as in the optic tract, myelin debris had been effectively cleared by one-month postoperative, while in the cranial segment of the nerve debris persisted for at least 6 weeks after injury. The differential pattern of myelin debris in the optic nerve and tract was then analyzed qualitatively and quantitatively using thick and thin plastic sections at various time points during regeneration. The results suggested that highly activated peripheral macrophages were responsible for the effective clearance of myelin in the distal nerve stump. In the optic tract a number of cellular properties, including their unique population of astrocytes may have enhanced the rate of debris clearance. By contrast, in the cranial segment of the nerve persistent debris was found both intracellularly in phagosomes and extracellularly, suggesting that the resident phagocytes were deficient in effecting both phagocytosis and emigration. Deficient phagocytosis may be a result of the production of anti-inflammatory cytokines in this region, while the failure to emigrate is most likely due to the rigid network of astrocytes in the nerve.