You all know that it was a rough summer in Nebraska. There is no doubt the drought has had some negative impacts on our fish and wildlife. For example, we have all been concerned about the fires in northern and western parts of the state and how, even though fire is a natural part of those ecosystems, those habitats, fish and wildlife will be changed for the rest of our lives. As summer turns to fall and hunting seasons begin to open and come to the forefront of our thoughts, there has been widespread concern about the impacts of EHD, epizootic hemorrhagic disease, on our whitetail deer populations. EHD is a disease that occurs naturally and likely kills a few deer many years, but it is known to be much worse when we have drought conditions, and that has certainly been the case this year. One last example, those of us who like to trap or do some predator calling are also aware of how sarcoptic mange has impacted our state’s coyote population in recent years.
And now our fish have lice. . . .
Look close at this picture of the side of a flathead catfish from Branched Oak Reservoir.
I said you had to look close, and even then you might not notice anything. Try this. . . .
Here is an even closer look:
What you see there is commonly called a fish louse. Technically it is a small crustacean, a copepod , that is parasitic on fish. There are a variety of copepods that bob around in our waters and can serve as important prey for small fish, but this particular species, Argulus sp. turns the table and parasitizes fish. For perspective, that fish louse on the flathead catfish was about the diameter of a #2 pencil. Fish lice attach to the side of a fish and then pierce the skin to suck blood–exactly like an aquatic tick or louse. They can damage the skin and mucus coat of a fish exposing it to a greater risk of secondary infections. As I understand it, adult fish lice live on fish, and will mate while on the fish, but they drop off the fish to deposit their eggs. Where the eggs are deposited, I do not know, somewhere in the water or perhaps on some bottom substrate or cover. As is true with other copepods, juvenile fish lice progress through several larval stages. They are free-swimming during some of those stages, but eventually they must find a fish to parasitize and repeat the cycle.
If you do a Google search for Argulus or fish lice you can find a bunch of magnified images that will give you a better idea of what these weird little creatures look like. Here’s one, from the Aqua Doc Lake and Pond Management website, http://aquadocinc.blogspot.com/2011/11/argulus-fish-lice.html .
Now do not go all “chicken little” about fish lice. I have handled thousands of fish in my life and can only think of a handful of times I have seen even one fish louse on a fish. In the past few years I have handled dozens of flathead catfish at Branched Oak Reservoir and I have seen fish lice on only one of those fish. No, I have not examined every square inch of every fish for “lice”, but I also have not seen any fish infested with lots of fish lice. On the flathead catfish of which I took the picture, there were maybe 4 or 5 fish lice on that entire 25-pound+ fish. I doubt that flathead even knew those little crustaceans were hitching a ride on its side. If a person was not observant, or looking for the lice, it would have been real easy to not even see them on that flathead catfish.
In rare, extreme, stressful conditions, small fish in particular may be infested with enough fish lice that the parasites might cause slower growth, secondary infections and even death. Most of the time, as is true with most of our fish parasites, the parasites are out there, they always are out there, but you will rarely see them, and they will rarely have any impact on our fish populations. We are NOT on the verge of some catastrophic fish lice outbreak.
Let me finish with a funny fish lice story. Some of my fellow biologists noticed a few fish lice on another Branched Oak flathead this summer and one of them wanted to take a few back to be preserved for future display. They did not happen to have any sample jars on the boat that day, so they used the next best thing–a pop bottle. The only problem is at some time that afternoon someone (who shall remain nameless) forgot the pop bottle was full of lake water and a few fish lice, and took a big gulp to quench his thirst. Well, I guess fish lice water tasted nothing like Mountain Dew and he turned about ten shades of green and did a little bit of “chumming” over the side of the boat. The fish lice are no threat to humans, even if ingested, but come to think of it, that person recently shaved his head!!!!!?????
Not really, just kidding.