Thesis (M.S.) - University of Tennessee, Knoxville, 2006. / Title from title page screen (viewed on Sept. 19, 2006). Thesis advisor: R. Bruce Robinson. Vita. Includes bibliographical references.

Thesis (M.S.)--Oregon State University, 2006. / Printout. Includes bibliographical references (leaves 33-38). Also available on the World Wide Web.

Thesis (M.S.)--Humboldt State University, 2007. / Includes bibliographical references (leaves 50-51). Also available via Humboldt Digital Scholar.

Thesis (M.S.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 57-68). Also available on the World Wide Web.

No description available.

Trout (Salmo trutta L.) were reared in a hatchery environment under a variety of temperature regimes, and patterns of early development and growth were studied. The period from fertilisation to 'first feeding' (i.e. when the yolk supply was almost exhausted) was described as a series of forty successive developmental 'steps'. A quantitative scoring system, whereby individual embryos were assigned points ranging from 1 to 1000 on the basis of assessment of numerous developmental features, was also developed. Trout reared at 10° achieved greater values of developmental score and standard length, but lower values of body mass, from a given quantity of yolk compared to trout reared at 2°. Yolk was used less efficiently for differentiation but more efficiently for growth in larger eggs. Although certain events, such as hatching, occurred relatively earlier at higher temperatures, the relative timings of most individual developmental changes, including myotube and muscle fibre formation and many aspects of neural development, did not vary with temperature. Muscle growth, particularly recruitment of new muscle fibres, was lower relative to developmental score and to length at 10° than at 2°. However, trout at first feeding of comparable total muscle area had significantly greater numbers of post-embryonic fibres when reared at the higher temperature, indicating the onset of a compensatory 'catch-up' in fibre recruitment. The effects of the migratory type of the female parent on development and growth of embryos and alevins were also investigated, but were found to be minimal. During a study examining the effects of forced exercise on growth, juvenile trout reared at 10° as embryos exhibited a greater potential for somatic growth and recruitment of new muscle fibres than those reared at 2°. It is postulated that this difference in growth potential is related to the higher numbers of myonuclei present in the 10°-reared fish.

1. Juvenile trout, Salmo trutta L., from three parental groups - sympatric Sea trout and freshwater-Resident trout, and isolated trout from above a waterfall impassable by upstream migrating anadromous trout - were reared under three ration regimes to manipulate growth rates. The development of seawater tolerance was studied by measuring drinking rates after periodic salinity challenges during the first two years of juvenile growth. No trout were observed to undergo the parr-smolt transformation in any of the parental form/ration combinations after two years in freshwater. However, a considerable proportion did mature during this time period. The proportion of maturing trout was directly related to ration level but was also influenced by parental form, with isolated trout demonstrating a greater tendency to mature early. Seawater tolerance increased with age in all groups. However, mean drinking rates upon salinity challenge were generally lower, from Experiment 2 onwards, in Resident trout than in either of the other two groups. 2. Eight immature sea trout (finnock) were radiotracked in the River Eden, Fife, during September, October and November 1994. The individual finnock displayed considerable variation in patterns of movement; two remained in freshwater for at least 27 days whereas others moved downstream out of the river within days or even hours of release. In general, this highlighted the transient nature of the freshwater migrations of some finnock, indicating that they move in and out of rivers over brief periods of time and apparently do not necessarily remain in freshwater continuously throughout the winter. 3. The hypo-osmoregulatory ability of finnock during the winter was assessed in two experiments. The number of finnock was limited in Experiment 1. Therefore, this was designed as a preliminary assessment of the physiological response of finnock to acute freshwater-seawater transfer. Osmoregulatory abilities were assessed by measurement of drinking rates, plasma ion and plasma cortisol concentrations after acute freshwater-seawater challenge and compared with freshwater-adapted and seawater-adapted control groups. Finnock displayed physiological responses typical of euryhaline teleosts upon seawater challenge; a rapid increase in drinking rate, an increase in plasma ion concentrations (but only to levels similar to, or slightly greater than, those of seawater-adapted fish), and increased plasma cortisol concentrations. The second experiment, in which numbers of finnock were greater, made use of the same techniques to assess the longer term acclimation of finnock to both freshwater-seawater and seawater- vi freshwater challenge, to establish whether finnock might suffer from a more subtle reduction in seawater-tolerance which would not have been necessarily apparent in the acute challenge of Experiment 1. Finnock did not appear to be physiologically compromised by seawater challenge during the winter months, and therefore, a breakdown in hypo-osmoregulatory abilities alone cannot be considered a reason for finnock returning to estuaries and rivers during the winter. 4. The physiological effects of low to medium levels of infestation of the ectoparasitic copepod Lepeophtheirus salmonis (Kroyer) on wild sea trout post-smolts were assessed at intervals during the development of the parasite. A mean infestation level of 18 parasites caused significant disruption to the osmoregulatory ability of hosts, as demonstrated by significantly higher plasma osmolality and chloride ion concentrations when compared with naive post-smolts. In addition, since no skin lesions were apparent on the hosts, these physiological effects were considered to be the consequence of larval attachment to the gill filaments, thereby possibly puncturing the epithelia and also damaging vital branchial ion excretory cells. 5. The modern molecular genetic RAPD-PCR technique was used to screen DNA of Lepeophtheirus salmonis collected from wild and fanned salmonid hosts from around the Scottish coasts. This technique indicated markedly different patterns of genetic variation amongst L. salmonis of farmed and wild origin, and between different farms. A number of genetic markers were found to be exclusive to, or at considerably higher frequency amongst, sea lice collected from farmed salmonid hosts. This technique established the possibility of assigning provenance to L. salmonis collected from wild hosts.

No description available.

Salmonid fishes have been reported to have a remarkable ontogeny of cone photoreceptors in their retina. The ultraviolet-sensitive (UVS) cones are of particular interest, as they disappear from, and reappear into, the retina. These events occur at times associated with migration to marine waters, and the return migration to freshwater spawning grounds, respectively. The primary goal of this thesis was to discover the mechanisms underlying this ontogeny of UVS cones by studying a salmonid, the rainbow trout (Oncorhynchus mykiss). Two hypotheses were considered: 1) UVS cones become dormant, similar to speculations regarding light damage of rod photoreceptors in albino trout; 2) UVS cones die and subsequently regenerate from stem cells known to robustly proliferate in trout retina. I cloned partial cDNAs of each opsin from trout and used them to develop in sjtu hybridization labelling of photoreceptors. I introduced the ability to assess UV sensitivity utilizing electroretinograms, and developed a polyclonal antibody against the UVS opsin, to label UVS cones in immunohistochemistry. I combined these tools to examine trout UVS cones during natural development, and found that it was similar to events during thyroid hormone (TH) treatment. I used labels and inhibitors of programmed cell death to determine that UVS cone death is a major mechanism of UVS cone disappearance. UVS cones reappeared into the retina following termination of TH treatment. Application of cell fate markers indicates that reappearing UVS cones can be generated from proliferating stem cells. Electroretinograms demonstrated that these regenerated UVS cones sufficiently integrate into the retina to pass signals onto second order neurons. This represents the only known example of cone photoreceptors regenerating from stem cells during natural development. I speculate on the adaptive value of the ontogeny of UVS cones. I also investigated mechanisms underlying the apparent survival of rod photoreceptors when albino trout retina receive light-induced damage. Previous conclusions in this area had been influential in forming the hypotheses of UVS cone ontogeny. Two hypotheses were envisioned: 1) rod photoreceptors were surviving light damage; 2) rods were being killed by light but quickly replaced by proliferating retinal cells. My results support the latter hypothesis.

An understanding of the level of both genetic and morphological diversity within a taxon and how that diversity is structured within and across habitats is important when determining the conservation value of that taxon and for successful habitat management programs to be developed. Atlin Lake is a large lake in northern British Columbia and is one of the largest lakes that contain relatively unperturbed populations of lake trout (Salvelinus namaycush). As the top aquatic predator, lake trout in Atlin Lake are a key component of the lake’s fish community and are important for local fisheries. I assayed lake trout from Atlin Lake and other western lake trout populations at eight microsatellite DNA loci and for body morphology to determine: (i) the level of genetic variation present, (ii) the level of substructure that occurs in Atlin Lake, and (iii) whether there was a relationship between the genetic and morphological variation present. STRUCTURE analysis identified five subpopulations within Atlin Lake. Morphological analysis was used to differentiate between the samples collected throughout Atlin Lake. Cluster analysis of size corrected data separated the fish into two groups making Atlin Lake the smallest lake identified to date to possess more than one morphotype. Genetic and morphological groupings were found not to be correlated with each other. Finally, I was interested in whether each of the genetic subpopulations contributed equally to the local fisheries catches. A mixed stock analysis of samples collected from the commercial fishery and recreational anglers indicated that all of the genetic subpopulations contribute to the fishery along with lake trout subpopulations in the interconnecting Tagish Lake; suggesting that no one subpopulation is being depleted by the fisheries. Continued genetic monitoring, however, is necessary to see if the trends in fishery contribution are temporally stable. Future studies should focus on understanding the source of the morphological variation and maintenance of genetic substructure. / Science, Faculty of / Zoology, Department of / Graduate