| Summary: | Stress in fish is ubiquitous in natural and anthropogenic environments, and has the
potential to cause major environmental and economic losses. Due to this, there is a need
to develop a broad range of tools in risk assessment that facilitate the objective detection
and assessment of stressed states in fish. It is well known that the exposure of fish to
stressful stimuli activates a highly integrated stress response system that encompasses
multiple levels of biological organization. At the organismal level, stress hormones (e.g.
Cortisol) are released into the circulatory system to mobilize energy stores, and at the
cellular level, heat shock proteins (e.g. hsp70) have functions related to preserving the
integrity of proteins. Given the similarities between these two levels of stress response
(i.e. maintenance of homeostasis), the purpose of my thesis was to determine if the
organismal (Cortisol) and cellular (hsp70) stress responses were functionally related. In
order to characterize this relationship, I: (1) studied a temperate salmonid (rainbow trout,
Oncorhynchus mykiss) and a tropical finfish (mossambique tilapia, Oreochromis
mossambicus); (2) measured the stress responses in hepatic and gill tissues; (3)
exogenously introduced Cortisol into fish via intra-peritoneal injections or dietary routes;
(4) artificially raised levels of Cortisol for acute (24 h) and sub-chronic (28 d) periods; (5)
applied different stressors, including heat stress (2 h, +12°C or 2 h, +14°C immediate
change), stress hormones (Cortisol), and toxicants (β-napthoflavone; bnf) to fish; (6)
characterized the stress responses at the organismal (i.e. Cortisol, glucose, and lactate) and
cellular (i.e. hsp70 and glucocorticoid receptor) levels; and (7) applied novel laboratory
techniques to describe the association between hsp70 and the glucocorticoid receptor. By
studying the stress responses under a variety of experimental conditions, I gained a
comprehensive understanding regarding the relationship between the organismal and
cellular stress responses in fish. The major findings included: (1) high levels of Cortisol
suppressed, or prevented, the heat stress-related increases of hsp70 in hepatic and gill
tissues of rainbow trout and gill tissues of mossambique tilapia; (2) sub-chronically
stressed fish (exposed to Cortisol or β-napthofiavone) could not mount an organismal or
cellular stress response when challenged with a heat stress; and (3) heat stress and
Cortisol exposure can promote the binding of hsp70 to the glucocorticoid receptor in fish.
Collectively, these findings demonstrate that a functional relationship exists between the
organismal and cellular stress responses in fish, and raises questions regarding the
existence of a highly interrelated and complex stress response system that spans all levels
of biological organization within the whole animal.
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