Past Research

Salmonid Physiology, Morphology, and Behavior

As a faculty research assistant at Oregon State University, I worked on a suite of studies under the Wild Chinook Surrogate Project. The aim of the project was to produce Chinook salmon Oncorhynchus tshawytscha that closely emulate wild fish (surrogates) for researchers who are studying dam passage, survival of naturally-produced fish, and fish navigation within reservoirs. Due to the ESA-listing of these fish, researchers are required to use hatchery origin surrogates. To produce these fish, we altered various factors such as density, substrate/habitat, diet, temperature, and flow and subsequently evaluated differences in physiology, behavior, and morphology throughout development.

I worked with many hatcheries across Oregon with the Fish Performance and Genetics Lab (FPGL) in Corvallis, OR and the Oregon Hatchery Research Center (OHRC) in Alsea, OR being the main two facilities. At the OHRC we were able to monitor in-stream movement of our surrogate fish in replicated artificial streams with video coverage and PIT tag array. The fish ladder at OHRC controls passage of migrating fishes to the upper basin of Fall Creek and permits collection of metric and genetic data on the fishes before assisting them upstream to spawn.

In addition to Chinook salmon, I also worked with Steelhead trout Oncorhynchus mykiss doing many similar studies and bull trout Salvelinus confluentus.

Check out our most recent publication Salinity effects on plasma ion levels, cortisol, and osmolality in Chinook salmon following lethal sampling. In this study we examined the hydromineral balance in fishes following euthanasia and found that plasma magnesium is more sensitive to physiological changes and responds more rapidly than sodium.

Fish Physiology — Climate Change and Thermal Stress

Critical thermal maxima of two geographic strains of Channel and Hybrid catfish

In this study critical thermal maxima is used as a physiological and ecological reference point to identify early signs of thermal stress. Since catfish production ponds in the Southeastern United States can have daily temperature maxima up to 36°C and daily fluctuations of as much as 6°C, it is valuable to assess whether regional genetic differences or hybridization influence survival or growth. We quantified differences of acute thermal tolerance in two geographically distinct strains of Channel catfish Ictalurus punctatus and their hybrid crosses with an industry standard strain of Blue catfish I. furcatus. The catfish were subjected to water temperature increases of 2.0±0.1°C per hour until they lost equilibrium. The southern strain of Channel catfish tolerated higher temperatures than the northern strain, and both strains of Channel catfish tolerated higher temperatures than their hybrid catfish strain.

My system                  IMG_8036

Effects of chronic thermal regimes on growth of two geographic strains of Channel and Hybrid catfish

To gain a more complete perspective of temperature effects on catfish physiological performance and growth it is important to examine long term effects as well as acute. To do this, we conducted a 6 week growth experiment where catfish were subjected to daily cycling temperatures of either 27-31°C or 32-36°C. These ranges were chosen to mimic daily pond fluctuations. Two geographically distinct strains of Channel catfish and a corresponding hybrid catfish were used. Hybrid catfish had the highest survival at both temperatures, and both strains of Channel catfish had greater growth at 27-31°C than at 32-36°C.

IMG_7691     Heather in the ponds

Seasonal blood chemistry response of sub-tropical nearshore fishes to climate change

To predict how future climate scenarios may impact sub-tropical nearshore fishes we examined blood-based physiological responses of three fish species to a suite of seawater conditions associated with future climate change. We chose Bonefish Albula vulpes, Yellowfin mojarra Gerres cinereus, and Checkered puffer Sphoeroides testudineus because they are common in sub-tropical and tropical mangrove ecosystems throughout the Western Atlantic and important to the local fisheries. Fish were exposed to an acute (30 minute) increase in salinity (50 ppt), acidity (decrease in pH by 0.5 units), or temperature (7-10°C), or temperature and acidity combined, and held in these conditions for 6 hours. Their physiological responses were compared across seasons. Bonefish exposed to challenges in the summer experienced greater blood-based osmotic and ionic disturbances compared to fish held in ambient conditions, with thermal challenges (particularly in the summer) being the most challenging. No significant treatment effects were observed for Yellowfin mojarra or Checkered puffer in either season. Together, results from this study demonstrate that acute climate-induced changes to thermal habitat will be the most challenging for sub-tropical fishes (particularly in the summer) relative to salinity and pH
stressors, but significant variation across species exists.

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Effects of acute thermal stress on ion and acid-base regulation in Channel catfish

To assess the physiological response of fish to daily temperature variations, hematological, metabolic, ionic and acid-base regulation were investigated in Channel catfish subjected to acute temperature increases from 28ºC to either 32ºC or 36ºC. Several biological parameters were analyzed from blood sampled from fish in each treatment. Arterial blood pH, bicarbonate (HCO3), partial pressure of carbon dioxide (PCO2), partial pressure of oxygen (PO2 ), hematocrit, hemoglobin, mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), glucose, lactate, total proteins, chloride (Cl), and osmolality all increased when Channel catfish were subjected to acute temperature change from 28ºC to 36ºC. With the exception of PCO2 and HCO3 there was no significant change between fish at 28o C and 32o C. The changes observed are very typical of acute stress in fish and suggests that acute temperature increase to 36ºC may by very stressful to Channel catfish and potentially the underlying physiological factor influencing critical thermal maxima (38.6-40.3ºC).

fingerlings 5       blood draw

Fish Physiology — Transcriptomics

Comparative transcriptomics of geographic strains of catfishes exposed to chronic high temperature

Following acute and chronic thermal studies on physiologic differences between two separate geographic strains of Channel catfish and their hybrid crosses with Blue catfish, we took it a level deeper and examined the differential expression of gene transcripts and regulated pathways of these fish. Eighteen cDNA libraries from liver samples were sequenced to obtain 61 million reads per library. This paper is in press so results cannot be released yet.

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Fish Physiology — Osmoregulation

Salinity effects on Atlantic sturgeon Acipenser oxyrinchus oxyrinchus growth and osmoregulation

To obtain a greater understanding of the osmoregulatory ability and habitat use of Atlantic sturgeon at early life stages, we examined whether salinity is a limiting factor for juveniles (2 months old). Juvenile Atlantic sturgeon were acclimated to one of three salinity treatments (0, 10, 33 ppt) representing the range of salinity they would be expected to encounter. Growth was measured over the proceeding 6 months and osmoregulatory ability, quantified by blood plasma osmolality and ionic concentrations, was measured after 4 months. All fish grew but fish in the 0 and 10 ppt treatments grew more than fish in 33 ppt. Blood plasma osmolality was regulated at similar levels regardless of salinity. Therefore, juvenile Atlantic sturgeon have the physiological capability to move between salinity habitats, but grow
faster in low salinities.

 DSC_2611        DSC_2639

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Fisheries Management

Laboratory investigation on the use of strobe lights and bubble curtains to deter dam escapes of age-0 Muskellunge

After observing countless stocked Muskellunge Esox masquinongy escape reservoirs over dams, we were curious to see whether a relatively low cost barrier or guidance system could be implemented to reduce this loss. Since success of such barriers has been mixed depending on species and nothing had been tried on Muskellunge, we examined the effectiveness of a simple bubble curtain, strobe light, and bubble curtain with strobe light barriers to deter Muskellunge from escaping over spillways. We found that age-0 Muskellunge are more likely to escape during the day than over the night and that none of the barrier types reduced rate of escape.

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