Does anyone know how long sea lice stays on fish after they hit freshwater?
Sea lice thrive only in saltwater. They die when their adult salmon hosts enter fresh water. How long sea lice can survive in fresh water is not yet known.
One study found that most lice fell off and died within two days of being in fresh water, but other studies have shown that over 60% of the lice were still alive after one week and that some survived up to three weeks in fresh water.
My own experience is that the egg strings are much more susceptible to the effects of freshwater. They seem to fall off within hours of the fish committing to freshwater. Perhaps this is a defense mechanism on the part of pregnant females to shed their eggs while they still have a chance to flush back out to the salt so they hatch in more hospitable conditions. The actual lice themselves seem to persist for days later.
If a fish flushes in and out of tidewater, the lice and their egg strings seem to survive for a prolonged period of time, presumably due to the continued availability of saltwater. I think this is why you will sometimes catch dark mature Kenai kings in tidewater that are quite red, their scales already starting to absorb into the skin, and yet still have spaghetti sea lice clinging to their flanks.
For an interesting and educational thread on sea lice, check out this link:
"Let every angler who loves to fish think what it would mean to him to find the fish were gone."
The KeenEye MD