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How long does it take for salmon to change colour after reaching fresh water?

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Compare coho in the ocean with coho ready to spawn.

Image from U.S. Fish and Wildlife Service on cybersalmon.fws.gov

How long do salmon survive in a river once they have left saltwater, and how quickly do they change colour once there?  For example, if I catch and release a very bright coho in a coastal river, is his lifespan only one or two days till spawning, or is it weeks?  I’m curious because when we catch a bright coho, my son says that the next day the fish would be too dark, but I think it must be several weeks before they turn dark.  We fish twenty to thirty miles downstream from the salmons’ spawning grounds and catch the salmon at a time when their eggs aren’t yet loose.  Under these circumstances, could the fish turn from silver dollar bright to spawned out red in two or three days?

Thanks for your expertise, this is a very helpful website and I appreciate your time.

Mikey

Professor Salmon’s reply:

Hi Mikey,

Depending on their species, salmon may be in freshwater upon their return from their ocean phase for many months.  For example, summer run steelhead (yes, a salmon, not a trout) enter freshwater from April to October and do not spawn until late February.  They hide out in deep, cool water pools during the wait.  Coho and other salmon you may be more familiar with may enter the river up to a few weeks before spawning.  Some sockeye are in freshwater just over a month before spawning.

As for their changes in colouration during this period, each species, watershed and individual fish responds differently in fresh water.  The length of time it takes a salmon to change colour depends on factors such as distance to spawning grounds, holding time in near-shore habitat prior to river entry, presence of a mate or population density, water temperature, and predation stress.  If you are fishing very close to their spawning ground or in short river systems, the salmon you see might change colour very rapidly, even within three to four days.

Professor Salmon