Thesis (Ph. D.)--Carleton University, 1992. / Also available in electronic format on the Internet.

Thesis (Ph.D. in zoology)--Washington State University, May 2006. / Includes bibliographical references (p. 93-96).

Thesis (Ph. D.)--University of Idaho, 2006. / Abstract. "May 2006." Includes bibliographical references. Also available online in PDF format.

Thesis (Ph. D.)--West Virginia University, 2006. / Title from document title page. Document formatted into pages; contains vi, 153 p. : ill. Includes abstract. Includes bibliographical references (p. 53-100).

No description available.

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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.

The effect of age and some environmental factors, especially light, on the vertical migration and distribution of Chaoborus flavicans larvae were studied both in the field and in the laboratory at Corbett Lake, British Columbia during the summer of 1963. Distribution and migration of Chaoborus larvae were studied largely by frequent horizontal Clarke-Bumpus plankton tows made at 1 metre intervals from the surface almost to the maximum depth of the lake. Marked differences were noted in daytime vertical distribution and diel migration of 5 size (or age) classes of larvae. These size classes probably corresponded approximately to larval instars. Class 0 and 1 larvae inhabited the epilimnion in the daytime throughout the summer, while class 4 larvae were largely confined to the hypolimnion during the day. Class 2 and 3 larvae occupied the epi-, meta-, and hypolimnion in the daytime during June and July, but were found chiefly in the hypolimnion during August and September. Only the older larvae (class 2, 3 and 4) underwent marked diel vertical migration which consisted of 4 phases: 1) daydepth, 2) ascent from day-depth to the surface, 3) gradual descent from surface, 4) rapid descent during dawn. The ascent occurred when subsurface light was rapidly diminishing at dusk, while the descent took place during darkness and was most marked when light started to penetrate the subsurface layers during dawn. Seasonal changes in timing of ascent and descent appeared to be correlated to seasonal changes in time of disappearance of subsurface light intensity during dusk. The rates of ascent and descent calculated from the analysis of echo traces were 13.6 and 1.1 m/hr respectively. Further analysis of the echo traces revealed that the Chaoborus scattering layer was in contact with the lake basin during daytime and descent, but not during ascent. Results from observations of larval migration in experimental tubes housed in a dark room corroborated those of the field. Class 2 larvae having similar daytime vertical distribution (surface and 5 m) as class 0 and 1 larvae underwent virtually no diel vertical migration in the tubes, while class 2 and 3 larvae taken from the deeper layers (10-14 m) of the lake did. The diel migration consisted of the same 4 phases observed in the field, as well as a "dawn rise" phase which was particularly evident for class 3 larvae. Complete migration cycles were induced by artificially changing the natural light intensity over an experimental tube during the period of relatively constant light (0900-1900 hours); the larvae responded most markedly to changes in light intensity at the 0-1000 lux range. Experiments indicated that the diel vertical migration of Chaoborus larvae is an exogenous rhythm controlled by light. / Science, Faculty of / Zoology, Department of / Graduate

Urine was collected from the trout (Salmfi gairdneri) using a cannulation technique. Total urine and electrolyte outputs decreased in smolts as compared with fresh water parr. The filtration rates, as measured using the inulin method, were concomitantly decreased in the smolts. No significant change of urine concentration, percent reabsorption or percent secretion of filtrate was recorded. There was a linear relationship between cumulative output and time indicating a steady flow rate. An increase in sodium and chloride content in the muscle was recorded during smolt transformation. Potassium and water content remained the same as in non-smolts. In the above group, the plasma sodium concentration increased. The decrease in renal output without dilution of body fluids is discussed with respect to a possible change in the extrarenal ion exchange mechanism. / Science, Faculty of / Zoology, Department of / Graduate

This study compares life-history characteristics of steelhead populations within a restricted area of the southwest coast of British Columbia, and within streams of the Pacific coast from central California to British Columbia. Variations observed within features of the life-histories of steelhead trout are related to physical features of stream environments and to the geographical location of study streams. Within British Columbia data relating to time of stream entry, sex ratios, repeat spawning, mean lengths and duration of fresh and salt-water residence of winter and summer steelhead have been obtained from samples voluntarily submitted by anglers. Data relating to study streams have been obtained from map study, personal observation and through the courtesy of various governmental and municipal agencies. Several published studies from the coastal United States have permitted comparison of steelhead populations over a wide geographic range. Within a limited area steelhead enter and ascend spawning streams throughout all months. Fish which enter streams between October 1 and April 30 are termed "winter steelhead*', while "summer steelhead" enter streams between May 1 and September 30. Cheakamus River is exceptional in that initial stream entry of winter steelhead is delayed until April 1, with most fish entering during April and May. Late entry is related to delayed freshet conditions within the stream. Almost twice as many female as male steelhead were angled. Comparison with trapping results suggests that sport fisheries select for females of anadramous rainbow trout populations. Repeat spawning of winter steelhead was found to range from 5.0 percent for fish from the Seymour River to 31.3 percent for Cheakamus River. Repeat spawning among summer steelhead ranged from 4.4 percent (Seymour River) to 6.3 percent (Coquihalla River). Mean fork lengths of steelhead populations of winter and summer steelhead showed little variation (range 26.3 to 31.0 inches). Winter steelhead from the Cheakamus River were larger than fish from all other populations, and summer steelhead from the Coquihalla River had the least mean length. Mean fork lengths of winter and summer steelhead were not significantly different, despite the five to eight month shorter term of salt-water residence of the latter. Variations of mean lengths of steelhead among different river systems is a result of differences in mean time of salt-water residence. Mean lengths increase with increased salt-water residence. Steelhead spent from one to four years in fresh water and from one to four years in salt water. Along the Pacific coast from Central California to southern British Columbia, timing of initial stream entry showed little variation and the sex ratio was near one male to one female. Repeat spawning decreases from south to north. Mean fork lengths of steelhead populations are greater and fish spend more years in fresh and more years in salt water in northern areas. Possible factors causing variations in life history characteristics of steelhead along the Pacific coast are discussed. / Science, Faculty of / Zoology, Department of / Graduate