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Carl B. Schreck

Publications and source records attributed to Carl B. Schreck.

47 records · Page 3Linked to original sources
USGS2011

Impacts of multispecies parasitism on juvenile coho salmon (Oncorhynchus kisutch) in Oregon

We are studying the impacts of parasites on threatened stocks of Oregon coastal coho salmon (Oncorhynchus kisutch). In our previous studies, we have found high infections of digeneans and myxozoans in coho salmon parr from the lower main stem of West Fork Smith River (WFSR), Oregon. In contrast parr from tributaries of this river, and outmigrating smolts, harbor considerably less parasites. Thus, we have hypothesized that heavy parasite burdens in parr from this river are associated with poor overwintering survival. The objective of the current study was to ascertain the possible effects these parasites have on smolt fitness. We captured parr from the lower main stem and tributaries of WFSR and held them in the laboratory to evaluate performance endpoints of smolts with varying degrees of infection by three digeneans (Nanophyetus salmincola, Apophallus sp., and neascus) and one myxozoan (Myxobolus insidiosus). The parameters we assessed were weight, fork length, growth, swimming stamina, and gill Na + ,K + -ATPase activity. We repeated our study on the subsequent year class and with hatchery reared coho salmon experimentally infected with N. salmincola. The most significant associations between parasites and these performance or fitness endpoints were observed in the heavily infected groups from both years. We found that all parasite species, except neascus, were negatively associated with fish fitness. This was corroborated for N. salmincola causing reduced growth with our experimental infection study. Parasites were most negatively associated with growth and size, and these parameters likely influenced the secondary findings with swimming stamina and ATPase activity levels.

Oregon↗
USGS2006

Quantitative evaluation of macrophage aggregates in brook trout Salvelinus fontinalis and rainbow trout Oncorhynchus mykiss

Macrophage aggregates (MAs) occur in various organs of fishes, especially the kidney, liver and spleen, and contain melanin, ceroid/lipofuscin and hemosiderin pigments. They have been used as indicators of a number of natural and anthropogenic stressors. Macrophage aggregates occur in salmonids but are poorly organized, irregularly shaped, and are generally smaller than those in derived teleosts. These features complicate quantification, and thus these fishes have seldom been used in studies correlating MAs with environmental stressors. To alleviate these complications, we developed color filtering algorithms for use with the software package ImagePro Plus ® (Media Cybernetics) that select and quantify pigmented area (i.e. colors ranging from gold to brown to black) in tissue sections. Image analysis results compared well with subjective scoring when tested on brook trout Salvelinus fontinalis and rainbow trout Oncorhynchus mykiss captured from high-elevation lakes or hatcheries. Macrophage aggregate pigments correlated positively with age and negatively with condition factor. Within individual fish, pigmentation correlated positively among organs, suggesting that the kidney, liver or spleen are suitable indicator organs. In age-matched fishes, MA pigments were not different between hatcheries and lakes in the organs examined. Between lakes, differences in pigments were observed in the kidney and spleen, but were not explained by age, condition factor, sex or maturation state. Our results indicate that quantification of the area occupied by MA pigments is an efficient and accurate means of evaluating MAs in salmonid organs and that organ pigmentation correlates with age and condition factor, as seen in studies with more derived fishes.

Diseases of Aquatic Organisms↗
USGS2005

p,p'-DDE depresses the immune competence of chinook salmon (Oncorhynchus tshawytscha) leukocytes

p , p ′-DDE, the main metabolite of DDT, is still detected in aquatic environments throughout the world. Here, the effects and mechanisms by which p , p ′-DDE exposure might affect the immune system of chinook salmon ( Oncorhynchus tshawytscha ) was studied. Isolated salmon splenic and pronephric leukocytes were incubated with different concentrations of p , p ′-DDE, and cell viability, induction of apoptosis, and mitogenic responses were measured by flow cytometry and Alamar Blue assay. p , p ′-DDE significantly reduced cell viability and proliferation and increased apoptosis. The effect of p , p ′-DDE on pronephric leukocytes was more severe than on splenic leukocytes, likely because pronephric leukocytes had a higher proportion of granulocytes, cells that appear more sensitive to p , p ′-DDE. The effect of p , p ′-DDE on leukocytes appeared to vary between developmental stages or seasonal differences. The mitogenic response of leukocytes of chinook salmon exposed to p , p ′-DDE in vivo exhibited a biphasic dose–response relationship. Only leukocytes isolated from salmon treated with 59 ppm p , p ′-DDE had a significantly lower percentage of Ig+ blasting cells than controls, although the response was biphasic. These results support the theory that exposure to chemical contaminants could lead to an increase in disease susceptibility and mortality of fish due to immune suppression.

Fish and Shellfish Immunology↗
USGS2001

Antibody-producting cells correlated with body weight in juvenile Chinook salmon Oncorhynchus tshawytscha acclimated to optimal and elevated temperatures

The immune response of juvenile chinook salmon ( Oncorhynchus tshawytscha ) ranging in weight from approximately 10 to 55 g was compared when the fish were acclimated to either 13 or 21° C. A haemolytic plaque assay was conducted to determine differences in the number of antibody-producing cells (APC) among fish of a similar age but different body weights. Regression analyses revealed significant increases in the number of APC with increasing body weight when fish were acclimated to either water temperature. These results emphasise the importance of standardising fish weight in immunological studies of salmonids before exploring the possible effects of acclimation temperatures.

Fish & Shellfish Immunology↗
USGS2000

Physiological status of naturally reared juvenile spring chinook salmon in the Yakima River: Seasonal dynamics and changes associated with smolting

Two year-classes of juvenile spring chinook salmon Oncorhynchus tshawytscha from the Yakima River, Washington, were sampled from July (3-4 months postemergence) through May (yearling smolt out-migration). Physiological characters measured included liver glycogen, body lipid, gill Na+-K+ ATPase, plasma thyroxine (T4), and plasma insulin-like growth factor-I (IGF-I). Distinct physiological changes were found that corresponded to season. Summer and fall were characterized by relatively high body lipid and condition factor. Winter was characterized by decreases in body lipid, condition factor, and plasma hormones. An increase in condition factor and body lipid was found in February and March. Finally, April and May were characterized by dramatic changes characteristic of smolting, including increased gill Na+-K+ ATPase activity, plasma T4, and IGF-I and decreased condition factor, body lipid, and liver glycogen. These results create a physiological template for juvenile spring chinook salmon in the drainage that provides a baseline for comparison with other years, populations, and life history types. In addition, this baseline provides a standard for controlled laboratory experiments and a target for fish culturists who rear juvenile spring chinook salmon for release from conservation hatcheries. The implications of these results for juvenile chinook salmon ecology and life history are discussed.

Washington↗
USGS1994

Variation in mitochondrial DNA and allozymes discriminates early and late forms of Chinook salmon Oncorhynchus tshawytscha in the Kenai and Kasilof Rivers, AK

Genetic differences between early and late forms of Alaskan chinook salmon ( Oncorhynchus tshawytscha ) were identified using two genetic approaches: mitochondrial DNA (mtDNA) analysis, and protein electrophoresis. Study populations consisted of early and late runs in each of the Kenai and Kasilof rivers in Alaska, and a population from the Minam River, Oregon. Two segments of mtDNA were amplified using the polymerase chain reaction (PCR) and digested with 14–16 restriction enzymes. Results showed that early runs were genetically similar to each other but different from the late runs. The late runs were different from each other based on the frequency of the common haplotypes. Frequency differences in shared haplotypes together with the presence of a unique haplotype separated the Minam River stock from those in Alaska. In the protein analysis, each population was examined at 30 allozyme loci. Based on 14 polymorphic loci, Minam River salmon were genetically distinct from the Alaskan populations. Within the Alaskan populations, early runs were most similar to each other but different from the late runs; the late runs were also genetically most similar to each other. Both mtDNA and allozyme analysis suggest that chinook salmon may segregate into genetically different early and late forms within a drainage.

Alaska↗
USGS1993

Seasonal changes in cortisol sensitivity and glucocorticoid receptor affinity and number in leukocytes of coho salmon

To determine if there were organ-specific changes in immune responses or immune-endocrine interaction, we monitored in vitro immune response, cortisol sensitivity and number and affinity of glucocorticoid receptors (GR) in leukocytes from freshwater-adapted juvenile coho salmon ( Oncorhynchus kisutch ) during the physiological changes that prepare them to enter the marine environment. During this period, absolute immune response declined, but splenic leukocytes generated more antibody-producing cells than did cells from anterior kidney. Splenic leukocytes were initially more sensitive to the suppressive effects of cortisol and had fewer GR than leukocytes from the anterior kidney. Leukocytes from the anterior kidney were initially insensitive to cortisol but developed sensitivity at about the same time as the dissociation constant and number of GR increased. In vitro incubation of anterior kidney leukocytes in cortisol altered GR variables when experiments were conducted during March through September but not during November through February. In some years, changes in GR or immune responses were correlated with plasma cortisol titers, but in other years there was no correlation. Thus, the exact relation between cortisol, GR and immune response in anadromous salmonids is unclear and other factors are involved.

Fish Physiology and Biochemistry↗
USGS1990

Changes in numbers of leukocytes in immune organs of juvenile coho salmon after acute stress or cortisol treatment

We examined the effects of acute stress and cortisol treatment on the number of leukocytes (normalized for fish body weight) in the blood, thymus, spleen, and anterior kidney of juvenile coho salmon Oncorhynchus kisutch . In acutely stressed or cortisol-fed fish, the numbers of leukocytes increased significantly in the thymus and anterior kidney, and decreased significantly in blood and spleen within 1 d after treatment. Numbers of cells in the anterior kidney, blood, and spleen returned to control levels by 3 d after treatment, but cell numbers in the thymus remained significantly greater than control values until 3–7 d after acute stress. Although dietary cortisol resulted in increased plasma cortisol titers and caused the same changes in leukocyte distribution as those caused by acute stress, the magnitude or duration of elevated cortisol levels and leukocyte numbers were not correlated. These results suggest that, although increased plasma cortisol titers induced by stress may be involved in the change in number of cells in various immune organs, factors other than cortisol are involved as well.

Journal of Aquatic Animal Health↗
USGS1983

Habitat Suitability Index Models: Longnose dace

A review and synthesis of existing information were used to develop riverine and lacustrine habitat models for longnose dace (Rhinichthys cataractae), a freshwater fish. The models are scaled to produce an index of habitat suitability between 0 (unsuitable habitat) to 1 (optimally suitable habitat) for freshwater, marine and estuarine areas of the continental United States. Habitat suitability indexes (HSI's) are designed for use with the habitat evaluation procedures developed by the U.S. Fish and Wildlife Service.

FWS/OBS↗
USGS1979

Resistance of different stocks and transferrin genotypes of coho salmon, Oncorhynchus kisutch, and steelhead trout, Salmo gairdneri, to bacterial kidney disease and vibriosis

Juvenile coho salmon and steelhead trout ofdifferentstocks and three transferrin genotypes(AA, AC, and CCl, all reared in identical or similar environments, were experimentally infected with Corynebacterium sp., the causative agent ofbacterial kidney disease, or with Vibrio anguillarum, the causative agent of vibriosis. Mortality due to the pathogens was compared among stocks within a species and among transferrin genotypes within a stock to determine whetherthere was a geneticbasis for resistance to disease. Differences in resistance to bacterial kidney disease among coho salmon stocks had a genetic basis. Stock susceptibility to vibriosis was strongly influenced by environmental factors. Coho salmon orsteelhead trout of one stock may be resistant to one disease but susceptible to another. The importance of transferrin genotype of coho salmon in resistance to bacterial kidney disease was stock specific; in stocks that showed differential resistance of genotypes, the AA was the most susceptible. No differencesin resistance to vibriosis were observed among transferrin genotypes.

Fishery Bulletin↗