<p>Teleosts take up metals by two major pathways: gills and/or gut. Past research is heavily focused on branchial uptake despite evidence that the gastro-intestinal tract (GIT) is the dominant route in some natural environments. To address this information gap, my thesis characterizes uptake mechanisms of Cd and Ca along the GIT of <em>Oncorhynchus mykiss</em>. Toxic effects of Cd, protective effects of Ca against Cd uptake, and Cd distribution within fish after ingestion are also explored.</p> <p>Four-week dietary Cd exposure affected growth and Ca regulation, while causing toxicity at the subcellular level. Elevated Ca in diets protected against accumulation and altered subcellular handling of Cd. Pre-exposure to different diets changed unidirectional uptake and binding rates of Cd and Ca, although they remained highly correlated. Binding rates of Cd to mucus can predict absorption rates of Cd<strong>.</strong></p> <p>A variety of <em>in vitro </em>and <em>in vivo </em>experiments on four distinct GIT segments (stomach, anterior-, mid-, and posterior- intestine) were undertaken to determine specific mechanisms of Cd and Ca uptake in freshwater trout. Cd transport was unaffected by solvent drag, but was stretch- and temperature- sensitive. Strong evidence for a common pathway for Ca and Cd transport was obtained. Cd also appeared to be taken up in part by zinc (ZIP-like) transporters and the divalent metal transporter DMT1. Ca uptake along the GIT appeared to be carrier-mediated, time- and concentration- dependent, but was not affected by solvent drag, or by Na concentration. Mucosal Cd did not inhibit Ca uptake. Ca, but not Cd, uptake rates were much lower in sea water-acclimated trout. Seawater and freshwater fish accumulated similar whole body Cd concentrations when fed contaminated diets for three weeks, but the majority of Cd in seawater trout remained in the posterior intestine tissue, while freshwater trout had higher internal burdens.</p> <p>This thesis advances the knowledge of metal uptake along the GIT of trout.</p> / Doctor of Science (PhD)

The Pacific Northwest is known for its once-abundant wild salmonid populations that have been in decline for more than 50 years due to habitat destruction and commercial overexploitation. To compensate, federal and state agencies annually release hundreds of thousands of hatchery-reared fish into the wild. However, accumulating data indicate that hatchery fish have lower fitness in natural environments, and that hatchery rearing negatively influences return rates of anadromous salmonids. Recently, mounting evidence revealed that the richness and diversity of intestinal microbial species influence host health. We examined the gut microbiota of pre-migratory hatchery-reared steelhead (Oncorhynchus mykiss) to assess microbial community diversity. The Cascade Mountains serve as an allopatric border between two distinct clades of steelhead that show significant differences in genomic and mitochondrial diversity. We identified differences in core microbiota of hatchery-reared fish that correlate with this divergent phylogeographic distribution. Steelhead sampled from hatcheries east of the Cascades had overall greater core gut microbiota diversity. These differences were found despite similarities in diet and rearing conditions. In addition to taxonomic variation across the geographic divide, we identified significant differences in metabolic pathways using PICRUSt gene prediction software. Our analysis revealed significant enrichment of genes associated with lipid metabolism in the gut microbiome of western fish. 8 of 19 individual lipid metabolism pathways were more prominent in western populations. Lipids are a vital nutritional component for teleost species involved in migration and subsequent return for spawning in natal environments. We hypothesize that the observed differences in lipid metabolism across this phylogenetic divide results from an increased ability of eastern Cascade (O. m. gairdneri) fish to utilize lipids taken in via the diet. This increased absorption and utilization would make lipids less available for the intestinal microbiota of the eastern fish, as evidenced by the lower abundance of lipid metabolism genes in the east. Our research utilizes information from the microbiome to understand the phenotypic implications occurring in segregated populations of hatchery-reared steelhead, further confirming elements of coevolution between an organism and its internal environment.

Responses of juvenile steelhead trout to changes in stream habitat resulting from an instream habitat rehabilitation project in Meadow Creek, Oregon were measured from 1991 through 1992 and compared to pre-treatment data from 1987 through 1990. Sixty nine pool-forming, and 59 channel-stabilizing log structures were constructed by the U.S. Forest Service in a 3.7 km reach in 1990. A 20-year flood caused extensive modifications to the instream structures in May 1991. Pool habitat and large wood volume increased in the treatment and the two reference reaches but pool development was greater in the treatment reach compared to the two reference reaches. Summer rearing densities of juvenile steelhead were similar for the treatment and the two reference reaches at the reach scale. Summer rearing densities were lower in the post-treatment period compared to the pre-treatment period for the treatment and two reference reaches. Mean density of juvenile steelhead was higher in complex pools compared to non-complex pools throughout the study area. Mean density of juvenile steelhead was higher in pools associated with large wood from washed-out structures compared to pools associated with intact structures in the treatment reach. Changes in smolt production from the treatment reach following the rehabilitation project could not be determined due to trapping difficulties. Only three percent of the smolts emigrating from the basin overwintered in the treatment reach in 1992. Four life history patterns of juvenile steelhead were identified. Only one of the four life history patterns rears in the Meadow Creek basin until smolting. From these findings I conclude that the instream habitat rehabilitation project did not increase the abundance of juvenile steelhead or smolt production during the first two years after treatment. An extended drought and a 20-year flood may have been the dominant factors controlling abundance of juvenile steelhead over the study period. The Meadow Creek rehabilitation project may have limited success at increasing smolt production because it influences only one of four life history patterns of juvenile steelhead during the entire freshwater rearing phase. / Graduation date: 1997

The evolution and maintenance of multiple phenotypes within populations is an interesting evolutionary and ecological question, and is becoming increasingly important for the restoration and conservation of partially migratory species. In particular, why individuals adopt a particular phenotype has been the focus of numerous research efforts. In the partially migratory species Oncorhynchys mykiss (commonly known as steelhead and rainbow trout), I found that sex plays a strong role in whether an individual adopts an anadromous or resident life history. I observed a higher frequency of females adopting the anadromous tactic throughout the species range, and I attributed this to the relationship between body size and reproductive success in females that is not present in males. I did not observe differences in female bias along gradients of latitude or migration distance, and I hypothesize that while the frequency of tactics among populations may change along these gradients, either the change is equal between males and females, or an interaction of latitude and migration distance may control changes. I did not observe a corresponding male bias in the one resident population I sampled, and suggest that this is the result of a high frequency of residents in that population. I propose that sex ratios could be a valuable metric for measuring frequency of life-history tactics in populations and could facilitate the investigation into the controls of life-history tactics across broad scales. / Graduation date: 2013

Visual estimation techniques were used to quantify habitat characteristics, habitat type (pool, riffle) use and longitudinal distribution of steelhead (Oncorhynchus mykiss), cutthroat trout (0. clarki), and coho salmon (0. kisutch) in spring, summer and fall in 8.8 km of Cummins Creek, a basin in the central coast of Oregon. Fish were distributed significantly different than habitat type availability in most samples. Pool habitats contained a disproportionate percent of the salmonid assemblage and 1+ fish in each sample, and the percentage of fish in pools increased as flow decreased. In spring, coho salmon fry were concentrated in side channels and valley floor tributary habitats. Large woody debris formed 57- 68% of pool habitats and was significantly correlated with pool volume, maximum pool depth, slow surface velocity in pools, and pieces of small woody debris. Longitudinal distribution of the salmonid assemblage did not differ from habitat distribution seasonally or between years, even though certain species differed Coho salmon and cutthroat trout were distributed in proportion to longitudinal habitat availability only when fish abundance was relatively high and streamflow was low. In most samples, both 0+ and 1+ steelhead were distributed in proportion to longitudinal habitat availability. Differences in coho salmon abundance between years appeared to influence longitudinal distribution of each species and age class. Certain reaches had consistent numbers of fish between years while the number of fish in other reaches varied widely. In most samples, reaches with highest abundance for steelhead were in the lower basin, cutthroat trout in the upper basin and coho salmon between the two other species. Timing of reduction in number of fish varied among species. Fifty-five percent of 0+ steelhead and 73% of 1+ steelhead lost between August 1988 and April 1989 were lost between August and October during low flow conditions. However, only 18% of the losses, for 0+ coho salmon, occurred between August and October with the remaining losses occurring after October. This study illustrates that habitat availability is not a good index of fish distribution when fish abundance is low, and it highlights the importance of habitat in the lower portions of basins when fish abundance is high. It also demonstrates that the basin wide distribution of salmonids varies among species, age classes, seasons, and years and suggests that our understanding of salmonid distribution and abundance could be greatly enhanced by adopting a basin-wide, community, and seasonal perspective. In addition, the methods used in this study offer one way to assess the seasonal distribution and abundance of salmonids in a relatively quick, inexpensive, and non-destructive manner. / Graduation date: 1994

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