The purpose of this work was to determine if environmentally-relevant
concentrations of chlorpyrifos and copper, two commonly detected chemicals in
Western surface waters, can negatively impact the biological health of salmonids.
Both compounds are highly neurotoxic to fish, but each with distinct biological target
sites and mechanisms of action. We used common biochemical and physiological
indicators of toxicity, and correlated these effects with potentially significant
behavioral alterations. For chlorpyrifos, the mechanism of toxic action is the inhibition
of acetylcholinesterase (AChE) throughout the peripheral and central nervous system.
Here, we conducted biochemical assays of AChE activity in brain and muscle tissues
after exposing steelhead trout (Oncorhynchus mykiss) and coho salmon (0. kisutch) to
chlorpyrifos for 96 hours. We then correlated the AChE inhibition with behavioral
impairment in swimming and feeding activities. In juvenile steelhead and coho
exposed to 0.6-2.5 ��g/L chlorpyrifos, AChE activity was inhibited between ~10-65%.
This biochemical indicator was significantly correlated with changes in behavioral
patterns. Spontaneous swimming rates were reduced ~30-80% in the exposed fish,
and strikes at food items (brine shrimp) were reduced ~10-70%. For copper and some
other neurotoxicants, the olfactory nervous system is a sensitive target site in fish. The
highly-developed olfactory system in salmonids is particularly susceptible to toxic
insult by dissolved chemicals since receptor neurons are in direct contact with the
aquatic environment. Here, we used electrophysiological techniques to record odor-evoked responses from the sensory epithelium and the olfactory bulb as direct
measures of olfactory function in juvenile coho salmon. In fish exposed to copper,
chlorpyrifos, or esfenvalerate for 7 days, field potentials recorded from the sensory
epithelium and the olfactory bulb showed reduced or obscured olfactory responses to
two classes of odorants, which activate non-overlapping populations of receptor
neurons. To determine if this reduced sensory input can subsequently alter or diminish
olfactory-mediated predator avoidance behaviors, paired physiological and behavioral
tests were conducted on juvenile coho exposed to copper. In fish exposed to 2-20
��g/L copper for 3 hours, olfactory sensitivity was reduced by ~50-9O%. When these
fish were presented with a predatory alarm cue (conspecific skin extract), fish with
reduced olfactory function increasingly failed to exhibit antipredator behavior. In the
following experiments, we show that chlorpyrifos and copper can impair the
biochemical and physiological biology of salmonids at environmentally-relevant
concentrations, and that these sublethal effects can alter potentially important
behavioral patterns. / Graduation date: 2004
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/30732 |
| Date | 17 September 2003 |
| Creators | Sandahl, Jason |
| Contributors | Jenkins, Jeffrey J. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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