The present study investigated the effects of stress and exercise on
seawater (SW) adaptation and cortisol dynamics in juvenile steelhead
(Oncorhynchus mykiss). To examine the effects of stress, fish acclimated to
freshwater (FW) were subjected for 3 hours to confinement stress in FW, and
subsequently SW (25 ppt) was introduced to all tanks. Fish were sampled
immediately after the stress treatment, and 1, 7, and 14 days after introduction of
SW. Electrolytes, cortisol, glucose and lactate followed the typical pattern that we
expected after stress treatment in FW. Fish regained osmotic balance within 24
hours. Glucose concentrations were increasing throughout the experiment and
lactate levels stayed elevated during the time spent in SW. IGF-1 did not show
an immediate response to stress but after transfer to SW we detected
significantly higher concentrations for control fish at days 1 and 14. The
differences in IGF-1 levels between stressed and control fish are not reflected in
SW adaptability but positive correlations between IGF-1 and electrolyte levels in
control fish may indicate its role for osmoregulation. Confinement stress did not
impair feed intake subsequently in SW, but our results suggest that feed intake
was suppressed by the change of the media from FW to SW.
The second study investigated the effects of exercise treatment in FW on
SW adaptation and cortisol dynamics in juvenile steelhead. Plasma cortisol and
in vitro cortisol secretion by interrenal cells after a 24 hr SW challenge test were
neither affected by moderate exercise nor by water temperature (13��C, 21��C),
however, plasma osmolality was lower in exercised fish compared to unexercised
fish. Half-life (T[subscript 1/2]) of ��H-cortisol was shorter in fish exposed to exercise whereas
metabolic clearance rate (MCR) did not respond to exercise treatment. Uptake
and retention of corticosteroids in liver and gall bladder were enhanced in
exercised fish, and retention of corticosteroids in muscle tissue was longer in
unexercised fish. Our findings suggest that exercise likely decreases stress
levels in fish and improves the adaptation to seawater (SW) in juvenile steelhead. / Graduation date: 2004
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/31053 |
| Date | 05 February 2004 |
| Creators | Liebert, Anja M. |
| Contributors | Schreck, Carl B. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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