Acid rain: acid makes fish more trusting

Posted on September 22, 2010

Chemical messengers play an important role in helping aquatic organisms to detect and avoid predators, locate food or mates, recognize kin and mark territories.  Because such chemicals degrade under acidified conditions, there are concerns that acid rain, which is caused by emissions from industrial activities, may reduce the fitness of freshwater animals and plants.  Canadian researchers prepared chemical alarm solution from extracts of the skin of Atlantic salmon, and injected it into a stream while snorkeling.   At the same time they made observations of salmon behavior which showed that fish responded to the presence of the alarm solution by foraging less and spending more time motionless on the bottom.   However, when these tests were repeated after a rain event caused the stream pH to drop from c. 6.9 to 6.2, salmon showed no significant reaction to the presence of alarm solution.   In lab experiments in which young rainbow trout were confronted by predators (largemouth bass) in aquaria containing alarm solution, they avoided capture for longer periods of time when the pH was neutral (7.0) than when it was mildly acidic (6.0).  These results suggest that the survival of freshwater species can be compromised during periods when stream pH is reduced by acid rain.  Taken together with recent findings from other studies, it seems that acid conditions both degrade important chemical cues and reduce the ability of organisms to detect them.

Reference:  Leduc, A.O.H.C., Roh, E. & Brown, G.E.  2009.  Effects of acid rainfall on juvenile Atlantic salmon (Salmo salar) antipredator behaviour: loss of chemical alarm function and potential survival consequences during predation.  Marine and Freshwater Research 60, 1223–1230.

Posted in: behaviour, fish, pollution