Discussion in 'Saltwater' started by Salvelinus, Sep 13, 2005.
Is it just me, or are larger male fish more likly to be coated with these things than female fish?
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...
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.
In case anyone is interested, there is a good article about this in the latest issue of Flyfisherman Mag.
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.
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.
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.