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Parr are brightly colored, with gold and silver
sides blotched with dark bars called parr marks. They also have red
spots on their back. These colors help hide the parr among the brightly
colored stones on the river bottom. They vary in colour to match their
surroundings. Parr hatched in tanks will grow to blend with the tank
colour. When they are released into a river it takes time for their
colour to adjust to the new surroundings. This makes them easily visible
to predators.
Smolts and adult salmon need a different color to
live at sea. They lose the red and gold, and parr marks of the parr.
Instead they develop a silver sheen on their sides, with a dark back
and a white belly. This way, predators have a hard time finding them,
because when a predator is above looking down on the salmon’s back,
the fish blends into the dark sea bottom. Similarly, a predator looking
up won’t see the salmon because its white belly blends in with
the water surface. And a predator looking sideways looks into the silver
mirror of the salmon’s side, and sees only the reflection of the
water. Salmon returning to a river from the sea change their silvery
colour to dark bronze until they go to sea again.
Salmon can see well and they use vision to locate
their prey. They can see colors, too. Salmon don’t hear. Instead
they use their lateral line receptors, which run down the center of
each side of their body to detect vibrations in the water. Some of these
vibrations can be caused by sound waves. So this is almost as good as
hearing. Salmon do not make noises like some other fish do, so maybe
they do not like sound waves in the water.
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