The migrations upstream of pre-spawned adult steelhead (Oncorhynchus mykiss) and
downstream of post-spawned steelhead (referred to as "kelts") can geographically and
temporally overlap in the Snake River, leading to management challenges for populations
listed under the Endangered Species Act (ESA). This thesis describes the development and
application of a method...
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...
Environmental factors such as chemical contamination can have immunomodulatory effects on the immune response of fish and may be contributing to the decline in salmonid populations by augmenting disease susceptibility. Xenobiotics can interfere with the immune system at several levels of complexity, and different immune cells and processes have variable...
The environment under which fish are maintained as broodstock before
reproduction is often stressful; however, the impact of stress on broodstock and gamete
quality is not well known. We investigated the effects of stress over the final stages (i.e.
the 3 months preceding ovulation) of sexual maturation of female rainbow...
Pacific lampreys (Lampetra tridentata) have declined in abundance in the Columbia River Basin. Although, the reasons for the decline are unclear, we suggest that development of hydroelectric dams and habitat alterations in tributaries as the main causes. The available knowledge of life history of Pacific lampreys and status from dam...
Sex differentiation in fish is a labile process that allows sex inversion in several species. The inherent capacity of fish germ cells to differentiate into oocytes or spermatocytes constitutes a key factor allowing for functional sex inversion. This thesis set out to determine the mechanism involved in steroid-induced sex differentiation...
Freshwater cyanobacterial blooms are a nuisance and health threat in the Pacific Northwest. The accepted methods of characterizing these blooms by microscopic cell counts cannot differentiate between toxic and non-toxic strains of the cyanobacterium Microcystis. Also, there is limited understanding of freshwater cyanophage that may control bloom dynamics. In order...
Alternative male phenotypes in salmonine fishes arise from individuals that mature as either larger and older anadromous marine-migrants or as smaller and younger freshwater residents. Variability in age and size of males at maturity is hypothesized to be preceded by early differences in growth in size and lipid storage. Water...
Early embryo development is dependent on maternally derived RNA and protein synthesized during oogenesis. In the bovine embryo this dependence lasts until the 8-16 cell stage, at which time embryonic transcripts become essential for continued development. One proposed mechanism for this transition from maternal to zygotic control of development (maternal...
While there are many more species of reptiles in the tropics than in temperate
latitudes, relatively little is known about the natural history of tropical species of
snakes. Even basic information, such as reproductive ecology and behavior, is lacking. Patterns of reproduction in tropical species differ from patterns in temperate...
The purpose of this work was to determine if environmentally-relevant concentrations of chlorpyrifos and copper, two commonly detected chemicals in Western surface waters, can negatively impact the biological health of salmonids. Both compounds are highly neurotoxic to fish, but each with distinct biological target sites and mechanisms of action. We...
Chinook salmon are the largest of any of the salmon in Oregon. Mature fish range from less than 2 pounds to more than 70 pounds. In the late 1800s, chinook salmon were almost the only species taken for canning in the Columbia River, with production peaking at 43 million pounds...
Coastal cutthroat trout is one of three cutthroat subspecies found in Oregon. The coastal subspecies, which is closely related to steelhead/rainbow trout and Pacific salmon, displays the most diverse and flexible life history of any of the Oregon salmonids. Coastal cutthroat can be found in streams and rivers from the...
The cultural and ecological values of Pacific lamprey (Lampetra tridentata) have not been understood by Euro-Americans and thus their great decline has almost gone unnoticed except by Native Americans, who elevated the issue and initiated research to restore its populations, at least in the Columbia Basin. They regard Pacific lamprey...
Anglers and naturelovers prize steelhead trout for their mystique and power. Oregon has two subspecies of steelhead (so-called because of the metallic appearance of maturing adults) or rainbow trout: a coastal form and an inland form.
I conducted field studies to determine the effect of insect herbivory and
intraspecific plant competition on ragwort Senecio jacobaea. The objectives were to
determine the patterns and causes in the distribution of the ragwort flea beetle
Longitarsus jacobaeae foraging among varying densities of ragwort, to measure the
behavioral and numerical...