Carbaryl, Carbofuran, and Methomyl - National Marine Fisheries ...

activity, they were subjected to a second exposure to determine if prior exposure altered
susceptibility to malathion. Swimming performance and AChE activity did not differ from
values of the initial exposure i.e., a second exposure resulted in no evidence of increased
susceptibility. Brook trout were the most sensitive based on AChE inhibition followed by
rainbow trout and coho salmon, respectively. AChE inhibition of 25% relative to control fish
occurred at 40 μg/L (brook trout), 55 μg/L (rainbow trout), and 100 μg/L (coho). Swimming
performance was affected at the lowest concentrations tested in each salmonid species and
showed a dose-dependent decrease in swimming performance as malathion concentration
increased. The data indicated that AChE inhibition of approximately 20-30% resulted in a 5% or
less reduction in swimming performance and as inhibition increased, swimming performance
decreased. Note, however, that the swimming test conducted in the study is a coarse measure of
swimming capacity. Thus, other non-measured swimming activity endpoints would likely be
affected at lower concentrations (Little and Finger 1990; Little, Archeski et al. 1990).
In summary, the information presented on swimming behaviors from AChE-inhibiting
insecticides provide a weight of evidence that carbamates (and OPs) adversely affect swimming
behaviors which can reduce the fitness of affected salmonids.
Assessment endpoints: Olfaction and olfactory­mediated behaviors: Predator avoidance, prey
detection and subsequent growth, imprinting of juvenile fish to natal waters, homing of adults
returning from the ocean, and spawning/reproduction
Assessment measures: Olfactory recordings (electro­olfactogram), behavioral measurements
such as detection of predator cues and alarm response, adult homing success, AChE activity in
olfactory rosettes and bulbs, and avoidance/preference
The olfactory sensory system in salmonids is particularly sensitive to toxic effects of metals and
organic contaminants. This is likely a result of the direct contact of olfactory neurons and
dissolved contaminants in surface waters. Olfactory-mediated behaviors play an essential role in
the successful completion of anadromous salmonid life cycles, and include detecting and
avoiding predators, recognizing kin, imprinting and homing in natal waters, and reproducing. It
is well established that Pacific salmon lose navigation skills when olfactory function is lost and
consequently are unable to return to natal streams (Wisby and Hasler 1954).
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