Does acidity impair the detection of damage-released chemical alarm cues in juvenile Atlantic salmon (Salmo salar).
Leduc, Antoine*,1, Roh, Ellie1, Harvey, Mark1, Brown, Grant1, 1 Department of Biology, Concordia University, Montréal, Québec, Canada
ABSTRACT- Damage-released chemical alarm cues play a critical role in the detection and subsequent avoidance of predators in aquatic environments. Responding to these cues translates into significant survival benefits for individuals. Several laboratory studies have shown that prey fishes fail to detect these critically important cues when the ambient pH reaches 6.0: threshold under which damage to the aquatic biota is argued to occur. However, only one field study has been conducted on this phenomenon, which examined only one fish population under acidic conditions against one fish population under neutral conditions. Since strain-dependant tolerance to acidity exists in different native fish populations, the ecological relevance of this phenomenon was difficult to assess. In our experiment, we conducted field observations in six nursery streams ranging in mean pH from 5.73 to 7.39 on two cohorts (0+ and 1+) of native juvenile Atlantic salmon (Salmo salar). We measured the intensity of an alarm response following the introduction of chemical alarm cues to assess if population differences in alarm response impairment are explained by the ambient pH. Our results demonstrated that salmon present in weakly acidified streams did not exhibit any overt response to alarm cues (i.e. not different from stream water controls), while those tested in streams of neutral pH exhibited a species-typical alarm response. While ontogeny did influence the response patterns in neutral conditions, no difference in response intensity was observable in weakly acidic conditions. These data suggest that damaged-released chemical alarm cues are generally ineffective in weakly acidified conditions (pHs that are physiologically suitable for Atlantic salmon, e.g. 6.0) demonstrating a potential sub-lethal effect of acidification on behaviour.
Key words: Atlantic salmon, Damage-released alarm cues, Stream acidification, Alarm response
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