Thesis (M.S.)--Oregon State University, 1977. / Typescript (photocopy). Includes bibliographical references. Also available via the World Wide Web.

Thesis (M.S.)--Utah State University. Dept. of Wildlife Science, 1973. / Includes vita. Includes bibliographical references (leaves 58-59).

Thesis (M.S.)--University of Wisconsin--Madison, 1961. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 31-34).

Thesis (M.S.)--Utah State University, 1973. / Title from title screen (viewed Aug. 13, 2009). Department: Wildlife Resources. Includes vita. Includes bibliographical references. Archival copy available in print.

Investigation of factors controlling seasonal changes in thyroid activity of juvenile steelhead trout (Salmo gairdneri Richardson) in fresh water revealed positive correlations between temperature and radioiodine assessments of thyroid activity. Temperature and thyroid epithelial height, however, showed negative correlations. These correlations were verified experimentally. In yearlings the thyroid was refractory to increasing photoperiod (January to July) but two-year-old potential migrants showed a positive response at the same season. Thus, the high smolt thyroid activity is induced by the combined influence of rising temperature and increasing spring photon period. Body mass (logarithm) was inversely related to various I¹³¹parameters (logarithm), so that small fish had higher thyroid activities than large fish. Precocious sexual maturation of two-year-old male parr, increased swimming exercise and increased salinity were associated with higher thyroid activity Increase in ambient I¹²⁷ depressed thyroid activity and indicated that the activity of the gland (assessed by current methods) is partly a compensation for low l¹²⁷ availability. The high thyroid activity of the smolt may be due partly to endemic goitre. Since low temperature and 8-hour daylength inhibited the thyroid activity of potential migrants but did not prevent silvering, the role of thyroxin in guanine deposition under natural conditions is doubted. Possible radiohormone catabolic sites were located in metabolically active tissues including gut, kidney, liver and brain. These findings suggest a general rather than a tissue-specific role of thyroxin in metabolism. It is concluded that thyroxin may have no stimulatory role in smoltification but reflects instead the total metabolic demands on the tissues. / Science, Faculty of / Zoology, Department of / Graduate

Variations in concentration, if any, of pharmacologically active principles of the hypothalamico-neurohypophysial system of the rainbow trout Salmo gairdneri during early periods of transfer to sea water were investigated. The concentrations of oxytocic and antidiuretic principles in the brains and pituitaries of handled fish, fish transferred to sea water, and fish transferred to fresh water, were measured employing the isolated virgin guinea pig uterus for assaying oxytocic activity, and the ethanol anaesthetized water loaded rat for assaying antidiuretic activity. Handling the fish resulted in an increase of oxytocic and antidiuretic activity of pituitary extracts. Transfer of experimental fish to a sea water environment resulted in a transitory increase of oxytocic activity of extracts of the pituitary and hypothalamus for the first and second hours with a subsequent return to control levels. After transfer of the fish to a sea water environment the antidiuretic activity of pituitary extracts was observed to decrease during the first and third hour, with a return to control levels at the sixth hour. This evidence suggests that active principles which are known to play active roles in water balance in animals higher, phylogenetically, than fish, are liberated from the hypothalamico-neurohypophysial system of Salmo gairdneri in response to a hypertonic environment. / Science, Faculty of / Zoology, Department of / Graduate

The role of such factors as distribution and movements of predator (Salmo gairdneri) and prey (Richardsonius balteatus), the activity involved in predation and the contribution of prey to the diet of the predator were studied in order to answer where, when, how and to what extent trout preyed on shiners. Data for 1955 and 1956 are compared with data for years when trout alone inhabited the lake. Predation became significant in 1950, approximately five years after the introduction of the prey species and has increased steadily, especially in trout over 10 inches in length, since that time. Movements of shiners in Paul Lake are complex and tend to bring this species into contact with trout during July, August and September. At this time shiners constitute over 90 percent of the diet of trout over 14 inches in length and lesser volumes in smaller trout. Trout under six inches in length prey on shiners to an insignificant degree. In winter shiners form a negligible part of the diet of trout of all sizes. Movement patterns seem to indicate that these two species might be separated in winter, and as a result predation is almost nil. It is inferred from the study that predation by trout is not a control of the number of shiners in the lake. The growth rate of trout under eight inches in length is still depressed as a result of competition with shiners for food. The contribution of shiners through predation, to the diet of larger trout, appears to have elevated the growth rate of trout eight to twelve inches in length, somewhat above that for years when trout alone inhabited the lake. The casual rather than causative nature of this predator-prey interaction is compared with the more stylized, obligate relationships of predator and prey in models of predation in the published literature. This relationship between rainbow trout and redside shiners is also discussed as it applies to management of lakes in which "sport fish" and "coarse fish" exist together. / Science, Faculty of / Zoology, Department of / Graduate

Reciprocal hybrid crosses were made of cutthroat and rainbow trout: and the eggs were reared under similar conditions with pure cutthroat and pure rainbow eggs. Viability of hybrid crosses was compared with viability of pure strains, and sex ratios in (offspring) were studied. Relative growth of several head and body parts was studied in the four lots of fish. Meristic comparisons, counts of teeth and pyloric caeca were made. Coloration was studied in all experimental lots of fish. Hybrid crosses were as viable as intraspecific crosses and sex ratios did not differ significantly from expected. Relative growth studies showed cutthroat had larger heads, larger head parts and deeper peduncles than rainbows. Hybrids were usually intermediate. Rainbow trout had higher scale, ray and vertibral counts than cutthroats. Contrary to most authorities, scale counts were higher on rainbows than on cutthroat. Dorsal ray counts for both hybrid lots resembled rainbow parents. Vertebral counts among hybrids tended to resemble female parents. No marked differences were found in teeth except on the hyoid bone. Pyloric caeca counts were similar in both parental lots. Coloration on rainbows was different than on cutthroats. Hybrids were intermediate in some aspects of color and in others they tended to resemble one parent. Eight samples of wild fish were examined. Several features which were distinctive in the hatchery fish were different for the two species in the wild. / Science, Faculty of / Zoology, Department of / Graduate

An investigation of the limnology and the Kamloops trout population of Raul Lake, British Columbia, from the summer of 1947 to the end of the summer of 1949, is presented. Comparisons of the conditions found by the writer are made with those conditions reported by Drs. C.McC. Mottley, D.S. Rawson and D.C.G. MacKay.in previous investigations of Paul Lake. Analysis of the environmental conditions indicated extreme annual variations in the summer heat income, an abundance of oxygen at all depths, minor annual fluctuations in the quantity of plantkon, a significant decrease in the quantity of bottom fauna which was believed due to the depletion of the Gammarus population, and a fairly large supply of available food. Another species of fish, the redside shiner, has made its entry into Paul Lake. The statistics of the trout population has shown a decrease in the average size of the age classes of trout since 1931, a large proportion of the younger age classes of trout in the anglers' catch and in the spawning run and a decrease in the size of eggs and number of eggs per female. A large year class resulting from 1945 has been followed through the fishery. The main effects of this year class appear to have been a greater survival of trout and a restoration of older age classes in the anglers' catch and in the spawning run. A comparison of the 1949 creel census data with that for 1936 has indicated a two-fold increase in fishing intensity, a slight decrease in the total catch and a decrease of two-thirds in the catch per unit effort. A revised stocking policy, patterned after the 1945 year class, is outlined. / Science, Faculty of / Zoology, Department of / Graduate

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 86-90). Also available via the Internet.