Jay Nicholas’ Salmon Fisher’s Journal: Field Observations on Sea Lice

Sea Lice are a parasitic copepod, and when we see these on our salmon, steelhead or cutthroat we consider these an indication that they have not been in the river (out of the ocean) very long.

Funny thing, though, I really didn’t know much about how long these critters could hang onto a fish, so I decided to report my field observations and do a little research to see what I could learn.

First – my field observations. This calls for four photographs to accompany descriptions.

I usually see these critters at the base of the anal fin. I have seen them almost everywhere on salmon fresh from the ocean, on the top of the head, on the back aft of the dorsal fin, and behind the adipose fin.

It is common (but not universal) to see dark patches at the base of the anal fin: these result from erosion of the scales and skin where the copepods have been clinging to the salmon. Sea lice associated with salmon farms (net pens) are thought capable of inflicting disastrous impacts on wild salmon in BC and Norway.

Photo 1 shows dark patches associated with the rasping of sea lice on an Elk River Chinook.

Jay Nicholas Sea Lice 1

The truest sign of fresh-from-saltwater sea lice is the presence of very long tails. These long tails drop-off pretty soon after the fish hits freshwater, maybe only a day or a few days at best. I don’t really know. I do know that this copepod makes a transition from being very translucent with very long tails, first looses its long filament tails, gradually becomes an opaque grey and eventually becomes dark brown.

Photo 2 shows the longest freshest tails I have ever seen on sea lice, these on a chum salmon fresh in on the morning’s tide.

Jay Nicholas Sea Lice 2

Photo 3 shows a still-translucent copepod on a chrome Elk River Chinook – note that the long tails have dropped off already. This fish was about 8 miles from the ocean and had been in freshwater at least a week. Note also that this fish did not have the dark erosion scars sometimes associated with sea lice.

Jay Nicholas Sea Lice 3

Photo 4 shows a rapidly graying, tails-long-gone copepod on a winter steelhead caught near Siletz.

Jay Nicholas Sea Lice 4

I found an interesting Internet site with sea lice factoids, although much of the information presented here is focused on treatment of net-penned (farmed) salmon.

This site states that sea lice can survive on salmon for up to 21 days in freshwater and that sea lice-bearing salmon have been observed about 30 miles from the ocean.

So here’s a question for all you blog-readers: how far upstream from salt water have you caught fish with sea lice in varying conditions – here in Oregon or elsewhere? I’d appreciate your stories and observations.


Jay Nicholas

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10 Responses to Jay Nicholas’ Salmon Fisher’s Journal: Field Observations on Sea Lice

  1. Jason says:

    I’ve found “lice” that look like those on multiple steelhead I caught this summer in Mecca Flats on the Deschutes.

  2. matt r says:

    I have landed a couple of chrome hens on the upper Nestucca over the years still bearing lice (although in each case, they appeared black). These fish were caught just above Blaine and also at the bridge below Outpost. No pictures available. . . this was back in the days of analog photography!

  3. Andy says:

    We’ve seen sealice on springers in the Willamette and Clackamas. I think they were all dark lice. Nice pictures. I never have looked for the tail on the lice but will do so from now on. Thanks. I like your blog by the way.

  4. kent says:

    I’ve caught bright steelhead with sea lice, in the Clemens Park area of the North Fork Alsea. The sea lice were dark, although the fish were very bright.

  5. Rob R says:

    I’ve seen sea lice on especially fresh fish in the Clack and Sandy rivers, but if you figure tidewater goes all the way to Bonneville and Willamette Falls, I guess it’s no major feat.

    I would have to see/hear some compelling evidence to buy sea lice on fish at Mecca Flats. Our rivers have loads of small dark leeches which are commonly mis-identified as sea lice.

  6. Cameron D. says:

    I’ve found sea lice in pretty good condition on silvers released around river mile 40 on the Umpqua.

  7. Jon Hazlett says:

    Jay, you never cease to amaze us with your creative and informative blogs.
    I have an old photo of a Rogue hatchery steelhead caught 10 years ago at Foster Bar, which is river mile 35, that has what looks like remnents of sea-lice.
    It was April 29. Not sure if it was an early summer or really late winter fish.

  8. Jay Nicholas says:

    God I love these fish. Thanks so much for the cool information and kind words. let’s keep the comments and observations coming. – and encourage everyone to take a close look at these fish. Seal marks. hook scars, areas of regenerated scales, sea lice, and the little leeches Rob mentioned. I once had a fellow tell me about catching a chrome steelhead “covered with sea lice” that was really slim, had pale flesh and tasted terrible. My guess is that the sea lice were really the little leeches, because sea lice rarely (really rarely) are found “all over” steelhead here in oregon. And it is not uncommon for folks to mistake a “slim re-silvered” kelt (spawned out) female steelhead for a fresh run fish. Anyway, keep the observations coming, keep fishin’, and loving these fish, and protecting their homes. JN

  9. tim says:

    heres a curve ball for ya. i live in sw wasington and do alot of my steelhead fishing on the east fork of the lewis. odd thing is i caught some old summers recently/12/6/ and they had very fresh sea lice, off white with long tails still intact.3 of 4 fish had them and they were inside the mouth and on gills with a few near the tail. any idea how this could be. these lice looked like they were in better shape than chromers ive pulled from the ocean

  10. Tim Kling says:

    Fishing yesterday on Skilak Lake for Silver Salmon, noticed sea lice on some of the fish caught. These fish have traveled approximately 50 miles up the Kenai River. We have had nearly flood stage river heights in the past 5 days. I have heard that sea lice live about 24 to 48 hours in fresh water, but I am not sure of this time frame. Any one with scientific back ground information could tell me would be appreciated. August 15, 2013

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