Imprinting to Chemical Cues: The Basis for Home Stream Selection in Salmon

Hatchery salmon were exposed to a synthetic chemical — morpholine — during the smolt stage, released, and eighteen months later streams were scented with the same chemical during the spawning run while recaptures were counted at scented and unscented sites.

Studied in

Oncorhynchus kisutch

Sample size

hatchery coho salmon exposed to a synthetic odorant as smolts

Salmon exposed as smolts returned overwhelmingly to the stream scented with that chemical, while unexposed controls did not.

• A single synthetic compound stands in for natural stream odour, which is a mixture nobody has fully characterised.
• Hatchery fish, released as a group; wild imprinting may differ in timing and in what is learned.
• Explains the final stream choice, not how a salmon crosses an ocean to reach the right coast.

• Teaching salmon a smell that exists in no river

  Do salmon return to a place, or to a smell they learned there? The two are impossible to separate — unless you supply a smell no place has.

• Salmon

  Salmon exposed to a synthetic chemical as juveniles returned years later to whichever stream had been scented with it. They were homing to a smell they had learned, not to a place.

• Salmon

  A river’s smell does not reach the open Pacific. Something else brings a salmon back to the right coast, and the best current candidate is the magnetic signature of the place it left.