From 1998-2000, laboratory studies were conducted to examine factors
that impact saltwater-entry behavior and saltwater preference (SWP) of juvenile
chinook salmon, Oncorhynchus tshawytscha. These factors included bacterial
kidney disease, stress and the presence of trout, O. mykiss. An additional study
investigated the orientation of the startle response of chinook salmon within a
salinity gradient. All experiments were conducted in 757-1 tanks in which a
stable, vertical salinity gradient was established. SWP was decreased in fish
suffering from bacterial kidney disease (31 �� 20.0%), compared with control fish
(85 �� 17.6%). A mild chasing stressor resulted in a 26% decrease in SWP relative
to unstressed fish. After a severe handling stressor, only 20% of fish preferred
salt water, compared with 100% of unstressed controls. After exposure to an
overhead predator model, severely stressed fish descended into the saltwater layer, but this response was transient. The presence of non-aggressive steelhead trout did not affect SWP of chinook salmon. Chinook salmon stocked with rainbow trout displayed decreased SWP. Aggression levels in tanks with
rainbow trout were higher than in tanks with only chinook salmon. The
orientation of the startle response was affected by the presence of salt water.
Fish that preferred salt water within a gradient responded by moving
horizontally within the saltwater layer. In contrast, control fish (held only in
freshwater) moved vertically within the water colunm when startled. Prior
preference for salt water superseded the inclination to move upward in the water
column when startled.
Smoltification involves physiological, behavioral and morphological
changes that prepare healthy chinook salmon for seawater residence. However,
disease, stress and aggressive interactions can decrease the SWP of fish at this life
history stage. Avoidance of salt water during estuarine outmigration is likely
maladaptive, and may have ecological ramifications including increased risk of
avian predation during outmigration and decreased fitness in the marine
environment. / Graduation date: 2002
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/32410 |
| Date | 09 April 2002 |
| Creators | Price, Carol Seals |
| Contributors | Schreck, Carl B. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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