Salmon is a species of high ecological and financial importance.
Migrating from its freshwater residence in a river out to Sea is a critical
step in every young Atlantic salmon's (Salmo salar) life,
and a necessity for the salmon to grow to large size. Researchers have long tried to understand what factors affect the young
salmon's decision to migrate out to Sea. Previous studies have indicated that
environmental factors such as temperature, light conditions and water flow may
play an important role. However, large parts of the within species variation in
fish migration remains unexplained. A study from Umeå University, published in the journal Nature
Communications, now
shows that the salmon's inclination to migrate is partly limited by its fear of
the unknown downstream. "By treating salmon with an anxiolytic drug, anxiety medication that
is, we artificially changed the migration intensity of the salmon where treated
salmon travelled further and faster than untreated salmon," says Gustav
Hellström, one of the researchers behind the study. The research team studied how salmon migration was affected both in a
lab, where salmon migrated in a large artificial stream, and in a natural stream
outside of Umeå in Northern Sweden. In both environments, researchers found that salmon treated with anxiety
medication migrated nearly twice as fast as salmon who had not been subjected
to treatment. Several billion animals migrate yearly and the results presented
here, i.e. that anxiety limits migration intensity, is not only important for
understanding salmon migration but also for understanding migration in general. The study also has an ecotoxicological dimension as the quantity of
medication that the salmon was exposed to was low - in fact so low that it
measured lower than that found in wastewater in certain areas. "Even though salmon in Northern Sweden live in river-systems low to
moderately affected by contaminated wastewater it is not very likely that
exposure to anxiety medication is an environmental issue for these populations
right now. However, given the low dose used in the study we cannot rule out
that, with increasing human population and medical use, this might become a
problem in the near future," says Gustav Hellström. 
Reproduced
with permission. Copyright The Fish Site | 
