Rearing environment affects spatial learning in juvenile Chinook salmon Oncorhynchus tshawytscha.

We tested the prediction that a complex physical rearing environment would enhance short-term spatial memory as assessed by learning ability in a spatial navigation task in juvenile Chinook salmon Oncorhynchus tshawytscha. We reared fish in two low-density treatments, where fish were either in bare fiberglass tanks (bare) or in tanks with physical structure (complex). We also tested conventionally reared high-density hatchery fish to compare with these other experimental treatments.

Egg size and growth in steelhead Oncorhynchus mykiss.

The effects of egg size on early development and growth of steelhead Oncorhynchus mykiss were recorded for more than 200 days following hatching. Fish from smaller eggs hatched sooner and at a smaller size than fish from larger eggs, but fish from smaller eggs showed consistently higher growth rates than fish from larger eggs. Since many life-history attributes appear to be determined by size or growth rate at age during the first year, egg size could be a significant predictor of important changes in the life history of individuals.

Stress up-regulates oxidative burst in juvenile Chinook salmon leukocytes.

When fish perceive stressful scenarios, their hypothalamus-pituitary-interrenal axis is activated resulting in the release of corticotropin releasing hormone, adrenocorticotropic hormone (ACTH), and finally cortisol. The physiologic stress response of fish has most often been linked to the reduced performance of the immune system, with a few exceptions where the immune system is activated. In this report, we tested the hypothesis that oxidative burst activity levels in juvenile Chinook salmon (Oncorhynchus tshawytscha) are altered when the fish is presented with a stressor.

The effect of rearing structures on behaviour and movement of juvenile steelhead Oncorhynchus mykiss.

The relative movement of juvenile steelhead Oncorhynchus mykiss reared on two treatments was investigated to provide insight on the effect of structure in the rearing environment on the behaviour of the fish before potential release into a natural river system. The progeny of wild broodstock were reared either in the presence or absence of structure in the tank environment for 7 months at the Oregon Hatchery Research Center located in Oregon, U.S.

Egg size and emergence timing affect morphology and behavior in juvenile Chinook Salmon, .

Variation in early life history traits often leads to differentially expressed morphological and behavioral phenotypes. We investigated whether variation in egg size and emergence timing influence subsequent morphology associated with migration timing in juvenile spring Chinook Salmon, . Based on evidence for a positive relationship between growth rate and migration timing, we predicted that fish from small eggs and fish that emerged earlier would have similar morphology to fall migrants, while fish from large eggs and individuals that emerged later would be more similar to older spring yearling migrants.

Salinity effects on plasma ion levels, cortisol, and osmolality in Chinook salmon following lethal sampling.

Studies on hydromineral balance in fishes frequently employ measurements of electrolytes following euthanasia. We tested the effects of fresh- or salt-water euthanasia baths of tricaine mesylate (MS-222) on plasma magnesium (Mg(2+)) and sodium (Na(+)) ions, cortisol and osmolality in fish exposed to saltwater challenges, and the ion and steroid hormone fluctuations over time following euthanasia in juvenile spring Chinook salmon (Oncorhynchus tshawytscha). Salinity of the euthanasia bath affected plasma Mg(2+) and Na(+) concentrations as well as osmolality, with higher concentrations in fish euthanized in saltwater.

Diet and cannibalism in plainfin midshipman Porichthys notatus.

The macroscopic and microscopic diversity of potential food items available in the nests of plainfin midshipman Porichthys notatus were quantified and compared with items that were found in the stomach and intestine (digestive tract) of the guarding males. In this species, males occur as one of two possible reproductive morphs: guarder males that care for young and sneaker males that parasitize the courtship and care of guarder males. Although it was predicted that guarder males would have fewer feeding opportunities due to their confinement to the nest, they in fact had more food items in their digestive tracts than did sneaker males and females.