Gill Lice

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I fish the southwestern corner of Wisconsin. The counties I frequent are Vernon, Crawford, Richland and Grant counties. Eleven years ago I caught a beautiful brook trout and it had some things attached to the gills. I took a photo of the gill section and forwarded it to numerous WDNR staff. I received responses from three fisheries folks right away. Mike Staggs, Gene Van Dyck and Dave Vetrano all told me about Gill Lice.

Gill lice (a parasitic copepod called Salmincola edwarsii) can cause significant physical trauma to the gill filaments, causing deformities which affect respiration and the efficient uptake of oxygen and the release of carbon dioxide, ammonia and other metabolites. Fish that are heavily infected cannot obtain sufficient oxygen when they are exercised, such as when they are caught by angling. Gill lice only attack Brook Trout.

Matthew Mitro, a coldwater fisheries research scientist for the DNR, said the fall shocking crews are out and about and will report on any declines in populations -- and also the water levels -- they might find.

I also contacted Susan Marcquenski the WDNR's fish disease specialist. I was concerned and asked her if the streams with gill lice in them should be closed. She answered with an emphatic "NO." She said rather than not fish the streams where gill lice are present, she would encourage people to fish and take fish home (reduce the density of the fish) as long as the fishing regulations allow this. Gill Lice are not dangerous to humans. Anything that can be done to keep water moving (faster velocity) may also help reduce the probability of larvae to successfully attach to fish. Beaver dams are breeding grounds for the parasite and all beaver dams need to be reported to your local fish manager.

This winter Matt Mitro contacted me again. He and his shocking crew had been at Ash Creek in Richland County in Fall 2012. His finding were very bad. Ash Creek is where the state has its nursery for the feral brook trout program. The brook trout population in that stream had taken a significant hit in population due to the Gill Lice. Matt took the photo attached. Matt wants the word out on Gill Lice and says please look at the photo and report any Gill Lice you find.

Since our conversation Trout Unlimited has put this Gill Lice reporting area on its website:
http://wisconsintu.org/Survey/tabid/468/Default.aspx

The treatment for Gill Lice is to individually dunk trout in a solution. The only problem with that is they can go right back in population and be re-infested. Gill Lice can be transferred by anglers on their gear from one stream to the next. The WDNR recommends that angler clean their gear with a bleach solution. One tablespoon of bleach to every gallon of water. This is to be sprayed on your gear prior to going to another stream. The WDNR says felt wading bottom boots are terrible for wading and infecting other streams.

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email to Matt Mitro TODAY:

I am wondering about stocking brook trout in streams with know Gill Lice infections?

Would it not only make sense to NOT put healthy brook trout in infected streams?

Any stocking should be done in streams with NO reported infections?

Maybe brown trout should be stocked again?

Len Harris

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Matt's response

Len,

These are all important questions. I don't think we have the data yet, however, to adequately answer all of these questions right now.

Host density (brook trout in this case) is a significant factor in whether or not gill lice become epizootic (infection rates rising to epidemic proportions). But it is likely not the only factor. We are trying to figure out what those other factors are.

Brown trout co-occurring with brook trout may be an important factor. One hypothesis is that brown trout may be effecting locally-high densities in brook trout. That is, brown trout may be pushing brook trout into locally-higher densities than may have occurred otherwise had brown trout not been present. If that is the case, then that would be one more reason not to stock brown trout on top of brook trout if we desire to keep brook trout in the stream.

The questions you raise are another reason why we need to compile data on gill lice presence and absence. Until we have those data, we cannot adequately implement such a stocking strategy.

Matt

[bgreer]

Interesting.

I know that in one of Missouri's trout parks, they have put in brook trout to keep parasite levels down to protect their rainbow population.

I think it started a couple years back and they have had some pretty good success with it. They put the brook trout in a pool above the rainbows, to "filter" out the bugs.

We all thought it was big news when we heard it. We thought that Missouri was going to be getting some brookies to fish for!

Brian