Sea Run Parasites 9/13

I'm told that these critters fall off very quickly once the cutthroat moves into fresh water. Smalma may be able to help us out with this take on the critters.



Active Member
Bob -
I have seen them in the north Sound area as well however as Les points outs I have never seen one on a fish in freshwater, the estuary of the larger rivers or the nearby bays with low salinity.



Native Trout Hunter
I have been catching a lot of cutthroat with both the parasitic copepod sea lice, and what ever the parasite is that I pictured above. In low densities, sea lice really do not have any noticeable adverse affects on fish, but they can be big problems when the show up in high densities.

One problem with sea lice is that they can be vectors for diseases such as salmon anemia which has had some devastating implications for fish farms. Sub-lethal effects of sea lice can also be a big problem, because although the lice fall off in the fresh water, they take away from the finite amount of energy that fish such as salmon which do not feed in freshwater have when they travel to their spawning grounds. Studies have also show that when fish are infected with high densities of sea lice their swimming ability is reduced, and are subject to chronic stress.

These issues can be a big deal when it comes to safetly releasing cutthroat or salmon that have a lot of sea lice. Making it much more important that the fish are fought and released quickly.

I still have no clue what the other parasite that I showed above is, but they are quite common in the south sound.

Dale Dennis

Formally Double-D
In my own abservations I started seeing this type of copepod (sea lice) in South Hood Canal on Searuns about the mid 90's, at that time there were few cutts that had this parasite. It has dramaticly increased over the years to almost epidemic porprotions. In the North Sound this parasite didn't begin showing up until the last several years. Another thing I have noticed that a few searuns will not have this parasite. Is it because they have just returned from fresh water (river) or have they come from and area that is not affected by the parasite? We don't know enough and it is becoming increasingly worse every year.


Active Member
I first saw this critter in 1974 - it was in Hood Canal and was on the first cutthroat I had ever caught in the Salt. I suspect that it has been around for a long time.

As with all parasites it is pretty common to see abundances wax and wan due to varying envirnomental conditions. One needs to only look at the common parasitic copepod found on trout in lakes. Over the last 30 years there have been periods when they were quite abundant in the lowland lakes over a wide area and other times where they were much rarer.

Just based on my observations and reports I have had from various anglers it still my be a good hypothesis that salinity may be an important factor in the abundance of this sea-run parasites. During periods of relatively low freshwater discharge (such as recent years) we may be seeing more parasites closer to the river mouths. Just an idea but it could be tested.

Tight lines


Active Member

As has been brought up before...struggling winter steelhead runs...salmon farms. There is the proof that the lice do attack adult fish. It's pretty easy to guess that the remaining wild winter steelhead juvenilies of PS tend to migrate or spend more time in the areas infested with the lice. And hence why they did not make much of a comeback this decade. Of course all of this is speculation. But based on what has happened to the sea trout (and salmon) in Europe and Canada where the net pens are located...


Bob Triggs

Stop Killing Wild Steelhead!
I am wondering if these lice attatch with a scolex, as some other parasites do. And if so, does exposing the scolex mechanisim to freshwater simply release the grip of the barbs of the scolex? That would exp[lain the loss of the lice in freshwater. And perhaps it is a simple matter of salinity or osmolarity, and the lice just let go and drift back to saltwater or get eaten.
The large ones that Ive observed in the south sound area may use a variety of means for attaching, Bob, but one means is suction, they have twin 'cups' around the front of them. Had a couple fall off onto the kayak sidewall after molesting them a bit, where they attached and stayed on, even after they dehydrated into copepod crunchies.
inland said:
But based on what has happened to the sea trout (and salmon) in Europe and Canada where the net pens are located...
In case anyone is interested, there is a good article about this in the latest issue of Flyfisherman Mag.


Sculpin Enterprises
I expect that Bob's thought that osmotic stress on the parasites as salmon and trout move from saltwater to fresh hits the mark. While there are some freshwater species of the sea louse (Argulus spp.), it is very rare that a primarily freshwater species can survive exposure to salt water and vice versa. A friend of mine who ran a small marine aquarium used to put the new fish that he had collected from kelp beds into a freshwater tank for thirty minutes. This low-tech, chemical free treatment was sufficient to cause the parasites to drop off or die, but the fish were not seriously impacted from the relatively short exposure.

The ability of salmon, trout, shad, lampreys, and striped bass (called anadromous fish) to survive under the hugely different osmotic / salinity regimes in salt vs. freshwater is amazing. In freshwater, fish pee a lot to dump the excess freshwater that enters their systems and absorb ions from their food and via cells in their gills to replace the ones that diffuse out. In saltwater, fish produce a concentrated urine to save water and excrete ions that diffuse in via cells in their gills. There are very few organisms that can pull off this physiological switch so effortlessly.

Curt's (Smalma's) thought that the outbreaks may be seasonal, due to extended periods of low flow (and high salinity) in late summer, is pretty interesting. Do folks have the impression that the parasite load on searuns caught in the marine environment is highest in the late summer, before our fall rains? Have people caught searuns in October - December (before most head into freshwater to spawn / chow on salmon eggs) that had high levels? I wonder if searuns can rid themselves of their parasite load by a quick freshwater exposure in either low salinity surface water after a rain or near a creek that is finally running with some oomph. In late summer, these sources are tough to find without a special effort, but after a few weeks of our usual fall weather, they should be pretty common conditions. You would expect that most fish in the spring would have very few parasites because they have just returned from their extended winter freshwater baths.


Bob Triggs

Stop Killing Wild Steelhead!
I definately see more lice on more fish (cutts) later in the season, into autumn. But I just figured that was because of time spent in the salt and the chance for the lice to become established and grow multiply etc.

Dale Dennis

Formally Double-D
Seasonal outbreaks is an interesting point. I know I see these (parasites) as early as the first of July in the North Sound. While not having made the seasonal observation in the past it will be interesting to see this October if this is possible. I do know that cutts will wander into river systems and lower estuaries and back to salt over a period of time.

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