Sexual maturation and sex differentiation comprise facets of a common theme: reproduction. The endocrine system regulates many of the critical physiological processes necessary for reproduction and offers a framework within which technologies can be developed for controlling sexual maturation and sex differentiation. The studies described in this thesis were undertaken to improve the understanding of the endocrine control of these critical stages of development in salmonids. Final ovarian maturation in salmon is accompanied by dynamic changes in plasma hormone levels. Ovulation can be accelerated through the use of hormones such as gonadotropin releasing hormone or its analogs (GnRHa). The effectiveness of GnRHa often depends on the timing of treatment. To determine if plasma concentrations of steroids can be used to predict the sensitivity of adult female coho salmon (Oncorhynchus kisutch) to GnRHa, circulating levels of testosterone, 17α,20β-dihydroxyprogesterone (DHP), and estradiol were measured before and after injection with GnRHa to accelerate ovulation. We found that high levels of testosterone were predictive of early response of coho salmon to GnRHa treatment. The correlation between testosterone and ovulatory response to GnRHa suggested a possible functional relation. However. implantation or injection of testosterone. 17α-methyltestosterone (MT), or the antiandrogen, cyproterone acetate (CA), before or with GnRHa treatment did not affect the ovulatory response of coho or chinook salmon ( 0. tshawytscha) to GnRHa. Chinook salmon treated with MT alone had accelerated ovulation in comparison to controls. If steroids are involved in sex differentiation. steroids must be produced early in development. In vitro production of steroids in both coho salmon and rainbow trout (0. mykiss) was assessed from hatch through sex differentiation. Cortisol, androstenedione, testosterone, and estradiol were produced just after hatching by tissue explants that contained anterior kidneys and gonads of coho salmon. To circumvent the problem of not knowing the sex of individuals until after sex differentiation, single-sex populations of rainbow trout were produced by gynogenesis or androgenesis. Tissue explants produced more androstenedione than testosterone or estradiol. More androgens were produced by testes and more estradiol was produced by ovaries within 6 to 10 weeks of hatching. Dietary treatment with estradiol or MT inhibited gonadal steroid secretion. Electrophoresis of gonadal homogenates from salmonids revealed several sex-specific bands. In particular, a prominent band of about 50,000 daltons was apparent in ovaries but not testes. Production of sex-specific proteins may be affected by dietary steroid treatment. / Graduation date: 1991

Erythrocytic inclusion body syndrome (EIBS) was artificially established in selected stocks of juvenile fall and spring chinook salmon (Oncorhynchus tshawytscha), chum salmon (0. keta), coho salmon (0. kisutch), Atlantic salmon (Salmo salar), and rainbow trout (0. mykiss). Adult spring chinook salmon were also artificially infected with the EIBS virus. Adult male chinook had higher prevalences of EIBS inclusion bodies than females. Cytoplasmic inclusion bodies that are associated with EIBS were not observed in steelhead (0. mykiss), brown (Salmo trutta) nor brook (Salvelinus fontinalis) trout suggesting that these stocks are less susceptible to the EIBS virus. Coho salmon with EIBS were more susceptible to Flexibacter psychrophilus, the causative agent of cold water disease (CWD) than fish without EIBS. The fish with EIBS were most susceptible to F. psychrophilus during the first 20 days after virus exposure, when inclusion bodies were most prevalent. Coho salmon infected with both the EIBS virus and F. psychrophilus required a longer recovery period than fish exposed to either pathogen alone. Most investigations of EIBS require in vivo experimentation and artificial infections using diseased fish tissues. Heterologous tissue used to establish EIBS did not contribute to anemia nor mortality. Death was not attributed to the EIBS virus alone but to the combined effects of the virus and a secondary pathogen. The severity of EIBS may be reduced with dietary Vitamin C prophylaxis. Fish fed 1,000 mg ascorbic acid/ Kg of diet had the fewest signs of EIBS; they had the highest hematocrit values and the lowest incidence of cytoplasmic inclusion bodies. However, vitamin C therapy alone was not sufficient to prevent the disease. / Graduation date: 1992

Lake trout (Salvelinus namaycush), chinook salmon (Oncorhynchus tschawytscha), coho salmon (Oncorhynchus kisutch), steelhead trout (Salmo gairdneri), and brown trout (Salmo trutta were collected from April 30 to November 18, 1970 with gill nets at selected sites in Lake Michigan near Gary, Burns Ditch, and Michigan City, Indiana. Catch-per-uniteffort was law and most catches occurred when nets were set in water temperatures in the 50 F (10.0 C) range or lower. Sea lamprey (Petrcnyzon marinas) scars and wounds were found on 25.4% of 71 lake trout captured and fresh wounds occurred on 6.0% of the fish. Scars and wounds were restricted to lake trout 20.0 in. (50.6 cm) or greater in total length and 32.7% of the 55 fish in this size group carried scars or wounds.Food items in stomachs of 39 lake trout, 34 coho salmon, and 29 chinook salmon were expressed as percent frequency of occurrence, numerical percent, and volumetric percent. The alewife (Alosa pseudoharenp_us) was the predominate food consumed by all three species. The crustaceans, Mysis sp. and Pontoporeia affinis, were consumed only by lake trout less than 19.0 in. (48.1 cm) total length.The age and growth of 69 known age fin clipped lake trout were examined. The body-scale relationship was TL = 6.2001 + 0.1238 Sc. The mean calculated total lengths for the first 5 years of growth were 5.3, 10.7, 16.3, 21.0, and 24.0 in. (13.5, 27.2, 41.4, 53.2, and 60.8 cm). Annual growth is considerably greater than recorded for Lake Michigan lake trout prior to alewife introduction and dominance. The length-weight relationship was log W = -2.5087 + 3.2338 log L which agrees closely with previous length-weight analyses of Lake Michigan lake trout.Ball State UniversityMuncie, IN 47306

Numerous techniques have been used to characterize ultraviolet polarization sensitivity (PS) in teleost fishes. To date PS in the rainbow trout (Oncorhynchus mykiss) has been characterized using compound action potential (CAP) recordings from the optic nerve. CAP recordings have also been used in conjunction with chromatic adaptation to isolate the individual cone photoreceptor mechanisms responsible for PS detection. The primary goal of this thesis was to discover the ancestry of PS within the Salmoninae clade containing Salmo, Salvelinus and Oncorhynchus, by characterizing and mapping the cone photoreceptor mechanisms mediating PS onto the phylogeny. I developed a research paradigm that used electroretinogram (ERG) recordings to characterize PS in rainbow trout. Substantial differences were found between CAP and ERG recordings. When identical stimuli were used, ERG recordings produced two additional peaks of maximal sensitivity at 45° and 135°. Chromatic adaptation was used to explore differences in bipolar cell and optic nerve generated PS curves. Under chromatic adaptation, with the use of ERG recordings, the additional peaks shifted consistently with the adaptation of either the horizontal or vertical polarization detector mechanism. These findings have contributed to the understanding of how ultraviolet polarized light is processed within the visual system I then used CAP and ERG recordings to characterize PS in Atlantic salmon (Salmo salar), because of its basal relationship within the Salmo, Salvelinus and Oncorhynchus clade. PS results obtained from CAP and ERG recordings were similar for Atlantic salmon and rainbow trout. CAP recordings generated a `W'-shaped PS curve maximally sensitive at 0°, 90°, and 180°, while ERG recordings generated a tuning curve with the additional peaks of maximal sensitivity at 0°, 45°, 90°, 135° and 180°. Therefore, it was concluded that both PS and the mechanisms of retinal processing underlying it are ancestral within the clade making up Salmo, Salvelinus and Oncorhychus. This has implications for the sensory abilities available when diadromous life histories evolved in Salmonidae.

The reproductive cycle of Coregonus lavaretus (L. ) in Loch Lomond was investigated by monthly sampling. The stages of the cycle occurred at the same time each year and were precisely timed. The environment followed a regular pattern which varied seasonally and was repeated annually. Spawning synchrony within the population during the short breeding period may be in response to lunar phases. A qualitative echosounding survey was made. The spatial distribution of the fish is probably related to their feeding behaviour and was mainly pelagic in summer and benthic in winter. Diel vertical migrations were recorded at dawn and dusk and appeared to be related to negative solar altitudes. The fish occurred at the surface during the night and persisted with their diel vertical migrations when feeding behaviour was benthic. The regulation of the reproductive cycle in the common sole Solea solea was investigated. The timing of spawning is ultimately determined by sea temperature, and spawning synchrony within the population is probably achieved in the initiation of exogenous vitellogenesis by a unified response within the breeding population to a stimulatory photoperiod. In both Solea solea and Coregonus lavaretus, initiation of exogenous vitellogenesis occurred during a rapid rise in the condition of the fish. The photosensitivity of the reproductive system may possibly be linked to a threshold condition. The pineal organ of Coregonus lavaretus is typically salmonid and the convoluted epithelium contained photoreceptors, interstitial cells, and neurones. The interstitial cells gave rise to processes which extended into the perivascular space. Photoreceptor cells synapsed with neurones, photoreceptor cells (lateral processes) and possibly other cell types. The results suggest that the pineal organ functions as a photoreceptor.

There have been numerous studies in which the reproductive cycles of teleosts have been correlated with either environmental cycles or associated physiological cycles, or both. Such correlation is seldom accurately achieved; usually because the reproductive cycle of the species concerned is lax, sometimes because only one or two factors of an integrated whole were examined. The powan of Loch Lomond, Coregonus lavaretus (L. ) (Teleostei, Salmoniformes) is the subject of a long-term study investigating its growth, in particular reproduction. This race is a freshwater glacial relict form of a boreal group, and thus has an exceptionally strictly times reproductive cycle. It thus represents an ideal subject for cyclical studies. This thesis investigates the relationship between lipid storage and the reproductive cycle and the role of thyroid gland.

No description available.

Thesis (M.S.)--Oregon State University, 1992. / Typescript (photocopy). Includes bibliographical references (leaves 64-70). Also available via the World Wide Web.

Thesis (M.S.)--Oregon State University, 1993. / Typescript (photocopy). Includes bibliographical references (leaves 120-125). Also available on the World Wide Web.

Thesis (M.S.)--Humboldt State University, 2009. / Includes bibliographical references (leaves 43-47). Also available via Humboldt Digital Scholar.