Born to Run?
Born to Run?

Author: Matthew R. Sloat

Publisher:

Published: 2013

Total Pages: 148

ISBN-13:

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Steelhead and rainbow trout are common names for marine-migratory (anadromous) and freshwater-resident forms of Oncorhynchus mykiss, a partially migratory salmonid fish. Anadromous and resident forms are sympatric and can produce offspring with a life history different from their own (i.e., steelhead parents can produce rainbow trout offspring and vice versa). The expression of these alternative life histories is a plastic response to individual patterns of energy acquisition, assimilation, and allocation during juvenile life stages. Individual performance during early stream life is of particular interest because of potential carry-over effects on subsequent growth and developmental trajectories. In a series of experiments in laboratory streams, I determined the influence of individual variation in energy metabolism on behavior, growth, and life-history expression in O. mykiss. Individual variation in energy metabolism was a strong predictor of feeding territory acquisition by juvenile fish during the transition from dependence on maternal provisioning of egg yolk reserves to independent feeding. Feeding territory acquisition was positively associated with standard metabolic rate (SMR) under conditions of an abundant and predictable food supply. When the density of intraspecific competitors was manipulated, the association between SMR and territory acquisition was strongest at intermediate stocking densities, moderate at the highest stocking densities, and weakest at the lowest stocking densities. However, reducing the spatial predictability of food resources within streams reversed the influence of SMR on competitive outcomes. These experiments determined that variation in ecological conditions during early life stages imposes different selection regimes on juvenile O. mykiss and results in physiological divergence among cohorts. Subsequent rearing experiments determined that behavioral dominance influences rates of anadromy and freshwater maturation, most likely through the association between SMR and territory acquisition. In addition to the effects of behavioral dominance, I observed a significant influence of sex, rearing temperature, and individual growth trajectories on the expression of anadromy and freshwater maturation. Partially migratory populations of O. mykiss maintain an exceptionally diverse portfolio of life-history strategies. Results from this work lend insight into a suite of behavioral and physiological processes influencing individual life histories.

Effects of Social Status and Food Availability on Predator Avoidance Behaviour in Young-of-the-year Rainbow Trout, Oncorhynchus Mykiss
Effects of Social Status and Food Availability on Predator Avoidance Behaviour in Young-of-the-year Rainbow Trout, Oncorhynchus Mykiss

Author: Mark C. Harvey

Publisher:

Published: 2005

Total Pages: 0

ISBN-13:

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Prey animals are often faced with a Hobson's choice: risk starvation or risk predation. Individuals capable of optimizing this trade-off through the use of context specific predator avoidance behaviour should be at a selective advantage. Food availability and social status have been shown to exert a strong influence on this trade-off, however, it remains unknown if these factors interact (i.e., do dominants and subordinates vary their behavioural decisions based on food availability). The purpose of this study was to examine the effects of food availability and social status, as well as their interaction, on the individual behaviour by young-of-the-year rainbow trout (Oncorhynchus mykiss) in response to perceived predation threats. Pairs of dominants and subordinates were assigned to either low, intermediate or high food availability treatments and exposed to either conspecific alarm cue (predation threat) or distilled water (no threat). The results suggest that an individual's response to a perceived predation threat is indeed dependent upon both social status and food availability.

Territorial Behavior in Juvenile Steelhead Trout (Oncorhynchus Mykiss)
Territorial Behavior in Juvenile Steelhead Trout (Oncorhynchus Mykiss)

Author: Craig A. Tinus

Publisher:

Published: 1999

Total Pages: 86

ISBN-13:

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Juvenile steelhead are known to associate with shiner groups, though they also compete for food. Steelhead form dominance hierarchies within cohorts and aggressively defend feeding territories against all other fish. This study focused on the differential effect of shiner competition on steelhead of different social standing. Survival of subordinate juvenile steelhead was significantly enhanced by the presence of redside shiner under laboratory conditions. A factorial experiment in 80 L tanks examined the relative effects of 0, 3, and 9 shiner at 15° and 20°C on the growth and survival of 3 juvenile steelhead per tank. No temperature effect was detected and there was no significant difference in steelhead growth though statistical power was low (n=5). The largest steelhead did not die in any treatment and no steelhead died in the presence of 9 shiner. In treatments where no shiner were present mortality in the smallest steelhead was 80% (p-value

Should I Stay Or Should I Go?
Should I Stay Or Should I Go?

Author: Geoff Koch

Publisher:

Published: 2015

Total Pages: 6

ISBN-13:

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Steelhead are the sea-going form of Oncorhynchus mykiss. Rainbow trout, also O. mykiss, remain in freshwater. Each form, or life-history, can produce offspring of the other, but the mechanism for this and potential effects that climate change may have on the species are poorly understood. Forest Service scientist Gordie Reeves, along with colleagues from other federal agencies and Oregon State University, conducted a series of studies to better document the biological processes that affect the life-history expression of O. mykiss. They found that standard metabolic rate and lipid levels play important roles: those fish with higher metabolisms and lower lipid levels tended to be steelhead, while those with lower metabolisms and higher lipid levels tended to be resident rainbows. Reeves' findings challenge the existing theory that faster growing individuals of the species tend to be seagoing steelhead. The research examined the effects of water temperature on life-history expression within the species. These findings offer clues about how climate change may affect the rainbow steelhead ratio in the years ahead. This research informs habitat improvement efforts and protection for steelhead populations, which are listed under the Endangered Species Act. It provides context, revealing how their life-history is interconnected with that of rainbow trout, which are not listed.