The brook trout population in a 4.7 hectare subarctic lake was sampled in 1986 and intensively fished in 1987, 1988 and 1989 in order to study the effect of stock depletion on fish parasite transmission. Population density was originally high, with slow individual growth rates, and small maximum size. Brook trout bore infections of Eubothrium salvelini, Phyllodistomum umblae, Crepidostomum farionis and Diplostomum sp. as well as some rare parasites. After intensive fishing the growth rates and size of the remaining fish increased. In 1987 all parasites increased in abundance. E. salvelini decreased in 1988 whereas the abundance of the other parasites remained high. In 1989 two new parasites, Echinorhynchus lateralis and Philonema sp. appeared. Parasite community changes and improves fish growth were related to trout diets and the pattern of intermediate host consumption. In 1987 zooplankton feeding increased. It then declined in 1988 and 1989 as populations of large benthic invertebrate prey increased. Feeding shifts may also have been mediated in part by intraspecific competition and aggression.

Cadmium (Cd) is a nonessential metal present in sublethal concentrations within the aquatic environment. Cd is an endocrine disruptor and high concentrations of this metal suppress stressor-induced cortisol production in fish. However, few studies have examined the effect of Cd at concentrations that are environmentally relevant on the functioning of the hypothalamus-pituitary-interrenal (HPI) axis. The HPI axis activity is essential in the stressor-induced cortisol production, a highly conserved adaptive response to stress in vertebrates. Elevation of plasma glucose in response to a rise in plasma cortisol is mediated through steroid activation of glucocorticoid receptors (GRs), but the mechanism of action of Cd in disrupting target tissue cortisol action is not known in fish. The overall objective of this thesis was to examine the impact of sublethal and environmentally relevant levels of Cd on the stress response and target tissue metabolic capacities, and to investigate the mechanisms of action of this metal in disrupting cortisol production and target tissue cortisol action in rainbow trout (Oncorhynchus mykiss). The impact of subchronic exposure to environmentally relevant levels of Cd on metabolic capacity and stress performance was identified through a 28 day (d) in vivo exposure of juvenile rainbow trout to either of two Cd concentrations (0.75 µg/L or 2.0 µg/L). During the exposure period, juvenile rainbow trout accumulated Cd within the liver, kidney and gills, but were able to adapt to exposure concentrations as no changes were observed in plasma cortisol, glucose and lactate levels. However, changes in abundance of mRNAs encoding proteins involved in corticosteroidogenesis, including melanocortin 2 receptor (MC2R), steroidogenic acute regulatory protein (StAR) and P450 side chain cleavage enzyme (P450scc), and liver GR protein expression suggesting endocrine disruption over the 28 d period. Also, target tissue metabolic capacities, including lower liver glycogen content and changes in intermediary metabolic enzyme activities in the liver and gill, were compromised by the 28 d exposure to Cd. The response to a secondary handling stressor at either 7 or 28 d exposure was attenuated suggesting that subchronic exposure to low levels of Cd disrupts the highly conserved adaptive stress response in rainbow trout. Upon further investigation using in vitro head kidney slices exposed to 0, 10, 100 or 1000 nM of Cd and stimulated with adrenocorticotropic hormone (ACTH), a similar inhibition of cortisol production was observed, as demonstrated in vivo, suggesting that Cd disrupts interrenal corticosteroidogenesis in fish. The impact of Cd on ACTH-stimulated cortisol production involved the suppression in the abundances of MC2R, StAR and P450scc transcripts. This response was also mimicked when head kidney slices from 7 d Cd exposed fish were incubated ex vivo with ACTH confirming that interrenal tissue is a key target for endocrine disruption by Cd. In both the in vitro and ex vivo incubations of head kidney slices 8-Bromo-cAMP (a cAMP analog) completely abolished the Cd-mediated cortisol inhibition demonstrating for the first time that Cd disruption of corticosteroidogenesis is occurring upstream of cAMP production. Further investigation of Cd-mediated impact on MC2R showed alterations in MC2R mRNA transcripts during in vivo exposure after 7 days and an attenuation of MC2R mRNA levels after Cd-exposed fish were subjected to a handling stressor. Disruptions in the mRNA abundance of MC2R was associated with disruptions of melanocortin receptor accessory protein 1 (MRAP1), but not MRAP2; a phenomenon that was also observed in ex vivo head kidney slices. Cell transfection studies confirmed that rainbow trout MC2R/MRAP1 receptor complex displayed decreased activity in the presence of Cd. Taken together these results suggest that Cd directly targets the MC2R/MRAP1 complex to inhibit ACTH-stimulated cortisol production in juvenile rainbow trout. In addition to Cd inhibiting interrenal steroidogenesis, the results also suggest that Cd may impact the negative feedback regulation of cortisol through the suppression of brain mineralocorticoid receptor (MR), but this requires further investigation. At the target tissue level, Cd by itself did not significantly affect liver metabolism, but inhibited the cortisol-induced glucose production in liver slices. This involved suppression of GR protein expression along with the suppression of GR-responsive genes, including phosphoenolpyruvate carboxykinase (PEPCK) and suppressor of cytokines signaling 1 (SOCS1) and changes in enzyme activities, including hexokinase, glucokinase, pyruvate kinase and PEPCK, pointing to a disruption in liver GR signaling by Cd. Altogether, Cd exposure disrupts the organismal stress responses in juvenile rainbow trout. Furthermore, Cd impairs the ability of juvenile rainbow trout to respond to a secondary stressor, which is a vital adaptive process that is fundamental to successful stress performance. Most importantly, these studies highlight for the first time that disruption of the HPI axis to attenuate cortisol production occurs at the level of the MC2R/MRAP1 complex, suggesting that the mechanism of action for attenuation of cortisol occurs at the level of MC2R activation. Also, GR signaling is a key target for Cd and may be a mechanism leading to altered metabolic capacities in stressed fish from Cd-contaminated sites. Overall environmentally relevant levels of Cd disrupt cortisol production and target tissue action of this steroid in rainbow trout.

Cadmium (Cd) is a nonessential metal present in sublethal concentrations within the aquatic environment. Cd is an endocrine disruptor and high concentrations of this metal suppress stressor-induced cortisol production in fish. However, few studies have examined the effect of Cd at concentrations that are environmentally relevant on the functioning of the hypothalamus-pituitary-interrenal (HPI) axis. The HPI axis activity is essential in the stressor-induced cortisol production, a highly conserved adaptive response to stress in vertebrates. Elevation of plasma glucose in response to a rise in plasma cortisol is mediated through steroid activation of glucocorticoid receptors (GRs), but the mechanism of action of Cd in disrupting target tissue cortisol action is not known in fish. The overall objective of this thesis was to examine the impact of sublethal and environmentally relevant levels of Cd on the stress response and target tissue metabolic capacities, and to investigate the mechanisms of action of this metal in disrupting cortisol production and target tissue cortisol action in rainbow trout (Oncorhynchus mykiss). The impact of subchronic exposure to environmentally relevant levels of Cd on metabolic capacity and stress performance was identified through a 28 day (d) in vivo exposure of juvenile rainbow trout to either of two Cd concentrations (0.75 µg/L or 2.0 µg/L). During the exposure period, juvenile rainbow trout accumulated Cd within the liver, kidney and gills, but were able to adapt to exposure concentrations as no changes were observed in plasma cortisol, glucose and lactate levels. However, changes in abundance of mRNAs encoding proteins involved in corticosteroidogenesis, including melanocortin 2 receptor (MC2R), steroidogenic acute regulatory protein (StAR) and P450 side chain cleavage enzyme (P450scc), and liver GR protein expression suggesting endocrine disruption over the 28 d period. Also, target tissue metabolic capacities, including lower liver glycogen content and changes in intermediary metabolic enzyme activities in the liver and gill, were compromised by the 28 d exposure to Cd. The response to a secondary handling stressor at either 7 or 28 d exposure was attenuated suggesting that subchronic exposure to low levels of Cd disrupts the highly conserved adaptive stress response in rainbow trout. Upon further investigation using in vitro head kidney slices exposed to 0, 10, 100 or 1000 nM of Cd and stimulated with adrenocorticotropic hormone (ACTH), a similar inhibition of cortisol production was observed, as demonstrated in vivo, suggesting that Cd disrupts interrenal corticosteroidogenesis in fish. The impact of Cd on ACTH-stimulated cortisol production involved the suppression in the abundances of MC2R, StAR and P450scc transcripts. This response was also mimicked when head kidney slices from 7 d Cd exposed fish were incubated ex vivo with ACTH confirming that interrenal tissue is a key target for endocrine disruption by Cd. In both the in vitro and ex vivo incubations of head kidney slices 8-Bromo-cAMP (a cAMP analog) completely abolished the Cd-mediated cortisol inhibition demonstrating for the first time that Cd disruption of corticosteroidogenesis is occurring upstream of cAMP production. Further investigation of Cd-mediated impact on MC2R showed alterations in MC2R mRNA transcripts during in vivo exposure after 7 days and an attenuation of MC2R mRNA levels after Cd-exposed fish were subjected to a handling stressor. Disruptions in the mRNA abundance of MC2R was associated with disruptions of melanocortin receptor accessory protein 1 (MRAP1), but not MRAP2; a phenomenon that was also observed in ex vivo head kidney slices. Cell transfection studies confirmed that rainbow trout MC2R/MRAP1 receptor complex displayed decreased activity in the presence of Cd. Taken together these results suggest that Cd directly targets the MC2R/MRAP1 complex to inhibit ACTH-stimulated cortisol production in juvenile rainbow trout. In addition to Cd inhibiting interrenal steroidogenesis, the results also suggest that Cd may impact the negative feedback regulation of cortisol through the suppression of brain mineralocorticoid receptor (MR), but this requires further investigation. At the target tissue level, Cd by itself did not significantly affect liver metabolism, but inhibited the cortisol-induced glucose production in liver slices. This involved suppression of GR protein expression along with the suppression of GR-responsive genes, including phosphoenolpyruvate carboxykinase (PEPCK) and suppressor of cytokines signaling 1 (SOCS1) and changes in enzyme activities, including hexokinase, glucokinase, pyruvate kinase and PEPCK, pointing to a disruption in liver GR signaling by Cd. Altogether, Cd exposure disrupts the organismal stress responses in juvenile rainbow trout. Furthermore, Cd impairs the ability of juvenile rainbow trout to respond to a secondary stressor, which is a vital adaptive process that is fundamental to successful stress performance. Most importantly, these studies highlight for the first time that disruption of the HPI axis to attenuate cortisol production occurs at the level of the MC2R/MRAP1 complex, suggesting that the mechanism of action for attenuation of cortisol occurs at the level of MC2R activation. Also, GR signaling is a key target for Cd and may be a mechanism leading to altered metabolic capacities in stressed fish from Cd-contaminated sites. Overall environmentally relevant levels of Cd disrupt cortisol production and target tissue action of this steroid in rainbow trout.

Characterization of the 5' flanking region of rainbow trout ki-ras gene was begun with the cloning and sequencing of this region by the inverse PCR technique and dideoxynucleotide chain termination method. In total, a nucleotide sequence of 1080 bp upstream from the first coding ATG was sequenced. Although this region showed certain promoter elements, it does not share common features with other mammalian ras promoters, which lack the TATA and contain multiple GC boxes with Spl binding activities. In contrast, this region in trout ras contains typical TATA and CCAAT boxes. This structural difference of the trout ki-ras promoter from that of other mammalian ras genes may suggest that different transcriptional regulation mechanisms of the ras ger.e are used at various levels in evolution. The chromatin structure of the trout ki-ras gene was studied by probing invivo for DNase I hypersensitive sites. To overcome the difficulties of using the traditional indirect end labeling method for a single-copy gene, the technique of ligation-mediated PCR was applied. No hypersensitive sites were observed at or near the codon 12 region of the gene, either in normal (protooncogene) or tumor (oncogene) tissue from the liver. This result suggests that the local chromatin structure of trout ki-ras gene may not be an important factor for codon 12 mutations induced by genotoxins, and that changes of chromatin structure are unlikely to be promoted after tumor formation. Studies by micrococcal nuclease demonstrate that this ras gene, in the region around 12, lacks ordered nucleosome positioning or may be even free of nucleosomes. Such an irregular organization of ras oncogenic chromatin would resemble that of many other "normal", highly active eukaryotic genes. The intrinsic affinity of trout ki-ras gene for aflatoxin B₁ was determined by in vitro alkylation experiments. Exon 1 of the gene was synthesized and labeled at the 5'end of the coding strand by the PCR technique. Taking advantage of the selective cleavage of AFB1-DNA adducts by piperidine under alkali conditions, the frequency of AFB 1 attack to each guanyl site was determined by densitometric scans after the cleaved fragments were electrophoresed on sequencing gels. The results demonstrated that two guanyl sites of codon 12 had differential affinity to AFBl, the more 5' G was relatively inaccessible but the more 3' G was accessible, indicating that the sequence selectivity of AFB I may contribute to the preference of the initial adduction in vivo. / Graduation date: 1993

This research focused on features of a genetically isolated population of cutthroat trout (Oncorhynchus clarki) in the Triangle Lake basin of coastal Oregon. A falls at the outlet of Triangle Lake has blocked upstream migration of trout and anadromous salmonids into the basin. Cutthroat trout were found throughout the six study streams of the Triangle Lake basin in association with other native fishes and introduced warmwater fishes. Warmwater species (e.g. Centrarchidae) were restricted largely to the lakes of Triangle Lake basin, and did not comprise a significant part of the stream fish fauna. Salmonids and cottids dominated the upper forested reaches of the basin, whereas nonsalmonids dominated the lower reaches. The middle reaches contained a transitional fish community between the upper and lower reaches. Reach type was a major factor influencing cutthroat trout density and size distribution. Areal densities of cutthroat trout were highest in the upper reaches and lowest in the lower reaches with the exception of 0+ cutthroat trout, which occurred at similar densities in all reaches. The highest frequency of 1+ cutthroat trout occurred in the middle reaches, whereas the highest frequency of 0+ cutthroat occurred in the lower reaches. Within reaches, channel unit type influenced the density and age structure of cutthroat trout. Pools and rapids had the highest densities of cutthroat trout, whereas riffles, glides, and cascades had lower densities. Larger trout were found primarily in pools and rapids. Planted steelhead fry (Oncorhynchus mykiss) were found in two streams, Congdon Creek and Lake Creek. Although most steelhead fry leave the basin as smolts, some steelhead appear to become resident and may hybridize with native cutthroat trout. Cutthroat trout spawning was observed from late December 1987 through late May 1988. Differences in the time and place of spawning may serve to genetically isolate two populations of cutthroat trout in Triangle Lake basin. One population may be lake dwelling as adults and spawn lower in the basin in late spring. The other population may be stream dwelling and spawn in the winter during higher flows, which allows them to spawn in the upper reaches of the basin. / Graduation date: 1994

Thesis (M.S.)--Oregon State College, 1948. / Typescript. Map of Crater Lake National Park and vicinity, issued by the U.S. Geological Survey, edition of 1946. Includes bibliographical references (leaves 118-120).

Thesis (Ph.D.) -- McMaster University, 1998. / Includes bibliographical references. Also available via World Wide Web.

Diss. (sammanfattning) Uppsala : Uppsala universitet, 2005. / Härtill 4 uppsatser.

Thesis (M.S. in zoology)--Washington State University, August 2008. / Includes bibliographical references (p. 41-44).

Thesis (M.S.)--University of Nevada, Reno, 2008. / "December, 2008." Includes bibliographical references. Online version available on the World Wide Web.