Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (leaves 98-109).

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

No description available.

Atlantic salmon (Salmo salar) parr-smolts were exposed to sublethal concentrations of cypermethrin, chlorothalonil, quintozene or atrazine to determine if they affected osmoregulation. After 96 h of exposure to a pesticide, Na+K+-ATPase, hematocrit, liver somatic index (LSI), plasma sodium, chloride, and cortisol concentrations were determined. There were no mortalities observed following a 24-h seawater challenge. No effects were seen with cypermethrin exposure. Chlorothalonil exposure resulted in increases in plasma Na+ concentrations following the seawater challenge in the 0.18 and 3.6 μg/L groups. For quintozene, decreases in LSI was seen at each concentration, and decreases in Na+K+-ATPase activity was seen at 0.55 μg/L as well as a decrease in Na+ concentrations at the highest exposure concentration. Atrazine exposure increased Na+K+-ATPase activity in the 1 and 100 μg/L groups, and plasma cortisol concentrations at100 μg/L. Overall, the pesticides examined had minimal effects on fish osmoregulation and stress at the concentrations tested.

The buoyancy (or density = mass volume-1) of marine larval fish is influenced by their nutritional status, starved larvae being less dense than fed larvae of like age. Buoyancy has, therefore, been proposed as an indicator by which to assess the nutritional condition of marine fish larvae in experiments and in situ. It has also been hypothesized that larval fish experiencing advanced starvation will exhibit increased density due to water loss resulting from osmoregulatory breach and failure. The magnitude of osmoregulation-related changes in density has not been examined and its influence on interpretations of nutritional condition and vertical distributions are unknown. Through a series of controlled laboratory experiments performed on larvae of cod (Gadus morhua L.), I developed evidence that osmoregulatory breach and failure has a strong positive effect on the density of larval fish, and that this effect on density is not limited to larvae experiencing advanced stages of starvation. These effects of osmotic breach and failure are sufficient to obscure effects resulting exclusively from nutritionally caused changes in density. Hence, if not identified and controlled these osmotically driven density changes can bias parameterization of buoyancy-related condition indices. I developed methods for isolating nutritional and osmotic effects. This facilitated the calibration of a nutritionally based density index with which to evaluate the nutritional state of cod larvae. Comparison of the calibrated density assay with a suite of widely used indices of condition (morphometric, behavioural and biochemical) showed density to be superior in its capacity to correctly classify larvae with respect to their nutritional state. The density index was also less subject to bias resulting from uncontrolled changes in larval size. A linear regression model based on these findings was developed to assess the relationship between density as an index of condition and near-term larval

Zebrafish, Danio rerio, are able to survive exposure to extreme acidity (pH 4). Because previous studies demonstrated that disruption of ionic balance during exposure to acidic water is the major cause of mortality in acid-sensitive freshwater species, the focus of this thesis was to characterize the molecular mechanisms enabling zebrafish to maintain their Na+ homeostasis following exposure to acidic water. Initial findings (Chapter 2) demonstrated that branchial mRNA expression of selected isoforms of claudins, major components of tight junctions, are altered in an isoform-dependent manner, suggesting the potential regulation of epithelial permeability to minimize ion loss. Concurrently, a marked stimulation of Na+ uptake was observed in adults and larvae following acid-exposure. Because of the uniqueness of this response (increasing Na+ uptake in acidic water) among freshwater teleosts, the mechanisms related to Na+ uptake and its stimulation were investigated further (Chapters 3 - 7). Pharmacological treatments and gene knockdown approaches revealed that a functional metabolon consisting of an apically expressed Na+-H+-exchanger (NHE3b) in association with an apically expressed ammonia-conducting channel (Rhcg1), enables Na+ uptake in acidic water. During chronic (>1 day) exposure to acidic water, cortisol (via glucocorticoid receptors) and catecholamines (via β-adrenergic receptors) are involved in stimulating Na+ uptake. Although catecholamines may act on both NHE3b and Na+-Cl- co-transporter (NCC), the effects of cortisol on Na+ uptake are mediated primarily by activation of NHE3b. On the other hand, during acute (<3 h) exposure to acidic water, cortisol does not appear to affect Na+ uptake; rather, the stimulation of Na+ uptake appears to be mediated by angiotensin II and catecholamines. Cyclic AMP (cAMP), a signalling molecule synthesized following the activation of β-adrenergic receptors, is critically involved in stimulating Na+ uptake, likely via activation of NHE3b and NCC. In agreement with this idea, ionocytes that express NHE3b also express high levels of β-adrenergic receptor (propranolol binding sites) as well as trans-membrane adenylyl cyclase (forskolin binding sites). Taken together, the results of this thesis provide fresh insight into the mechanisms of osmoregulation in freshwater (FW) fish. In particular, the data reveal the presence of complex pathways regulating Na+ uptake in zebrafish exposed to acidic water. The relative importance of the various pathways depends in part on the duration of exposure; acute versus chronic.

Population fragmentation is a common symptom of the decline of species, including freshwater fishes. It occurs naturally, but has also proliferated in response to human interventions that increase the prevalence and intensity of isolating barriers and events. In regulated rivers, for example, fish are affected by the loss of connectivity between habitats that is associated with hydrological changes. The process has evolutionary consequences by limiting gene flow, reducing genetic diversity and rendering the isolates vulnerable to local environmental changes. Comparative studies of related species may help to elucidate the causes and consequences of fragmentation. For example, they may identify habitat features that influence the spatial separation of congeneric species. An opportunity for such a study arises with small fishes (Atherinidae) in the intensively-regulated River Murray, southeastern Australia. Whereas the unspecked hardyhead Craterocephalus stercusmuscarum fulvus is widespread and abundant, the Murray hardyhead C. fluviatilis has a patchy distribution and is listed as 'endangered‘ by the International Union for Conservation of Nature and 'vulnerable‘ under the Australian Environment Protection and Biodiversity Conservation Act 1999. These two species rarely cohabit, implying that they could be separated by particular habitat characteristics. In the past, several species of Craterocephalus, including C. fluviatilis and the Darling River hardyhead C. amniculus, have been regarded as C. eyresii sensu lato. The taxonomic separation of C. s. fulvus has been confirmed, but some doubt remains about the relationship of C. fluviatilis and C. amniculus. This issue needs resolution to ensure that appropriate targets are set for conservation. This study is a comparative investigation of the aforementioned species. It was designed (1) to identify the habitat characteristics that influence the distribution and abundance of C. fluviatilis and, given that salinity emerged as a key factor, (2) to explore the biological implications of salinity through a comparative study of osmoregulation in C. fluviatilis and C. s. fulvus, (3) to determine whether the osmoregulatory responses of population isolates of C. fluviatilis differ at varying salinities, and (4) to evaluate the genetic population structure of C. fluviatilis, confirm its taxonomic separation from C. amniculus and identify genetic 'management units‘ for conservation. Field sampling showed that C. fluviatilis is confined mainly to saline waters (0.4-20‰), whereas C. s. fulvus is absent from salinities >7‰. Comparisons were made of osmoregulation in these two taxa over a salinity range of 0.03-85‰, with additional reference to the small-mouth hardyhead Atherinosoma microstoma, a related estuarine species that tolerates salinities >94‰. The three species all are euryhaline, although the osmoregulatory ability of C. s. fulvus falters above about 35‰ salinity. C. fluviatilis is a better osmoregulator than A. microstoma at salinities <1‰, but both species tolerate hypersaline conditions (85‰). Osmoregulation was compared in C. fluviatilis from two isolated populations in different salinity regimes (Wyngate: 0.4-1.5‰, Disher Creek: c. 1.0-45‰) to determine whether they show related phenotypic differences. Fish from both populations remained healthy at salinities from 5-65‰. The Disher Creek population maintained a significantly lower blood osmotic concentration than the Wyngate population at salinities ≤1‰, suggesting that there is a physiological difference between them. The genetic population structure of C. fluviatilis and its taxonomic distinction from C. amniculus were investigated using complementary allozyme and mtDNA markers. This confirmed that C. fluviatilis is genetically distinct from its sister taxon, C. amniculus. It also identified several genetically-defined 'management units‘ as a framework for future conservation. Further, it revealed that C. fluviatilis in habitats downstream of Lock 1 on the Murray (274 km from the river mouth) displays a genetic signature indicating introgression with C. amniculus. Clearly, these findings have implications for the conservation of C. fluviatilis. For example, isolates can be prioritised for protection, and re-introduction programs can be modified accordingly. The findings may be applied to other freshwater fish, especially populations of closely-related species subject to salinisation or other stressors, and they may also contribute toward understanding of the factors and processes underlying rarity and fragmentation. It is clear that salinity can be a significant factor in population fragmentation, and that closelyrelated species with similar ranges may be segregated by differences in osmoregulatory ability. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1363300 / Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2009

Thesis (M.S.)--Brock University, 2006. / Includes bibliographical references (leaves 105-118).

Zugl.: Leipzig, Univ., Diss., 2009

Thesis (Ph.D.) - University of St Andrews, May 2008.