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Anchor Worms at Dowdy and other Fisheries

Blog by: David Coulson 11/7/2013

Recently I got an email asking what the sores were on trout being caught at Dowdy and other Red Feather Lakes. This topic has come up in pervious forum posts.  Ive seen them myself over the years, and honestly Ive not paid them much mind as the fish appeared otherwise fairly healthy, the fish with sores were only occasionally caught, and I was releasing everything.

I did a quick internet search and failed to get satisfactory results, and suggested he contact CPW for an answer, to which he did and he was good enough to share the response with me, and consequently Im passing it along with minor editing.

The original email to CPW:

What are the pink, round, bulging and sometimes open and bleeding sores on the trout in Dowdy Lake at Red Feather Lakes, CO in Larimer County?  Every fish we saw had some from several to many sores.  Each lesion was about the size of a pencil eraser or a little larger.

CPWs response:

Good Morning --

According to our Sr. Aquatic Biologist, Ken Kehmeier, Dowdy lake has a parasite called Lernia or Anchor worm that impacts the fish.  During the summer the fish would appear to have small hair like organisms that protrude from the area of the back around the dorsal fin.  As the water cools those adult female parasite releases from the fish and will leave the sore referenced in the email.  Those sore will heal up over the winter and fish will look normal, only  to see the the problem arise again next summer. The fish are OK to eat and the angler can either cut the sore out of the meat or at least make sure the fish is cooked adequately.

Lernia has a life cycle that uses the fish for the adult form and the alternate host is the snail found in the lake.  There is no way to rid the lake of this parasite, and ultimately it does not have a huge impact on the fish other than unsightly fish. 

I hope this answers your question.  If I can be of any further assistance, please feel free to contact me at any time.  You can also contact Ken in our Fort Collins office at or at 970-472-4350.

Carol Bowser
Colorado Parks &Wildlife
6060 Broadway
Denver, CO  80216


First off, I'd like to thank everyone for sharing this, especially CPW who Ive always found to be responsive to reasonable information requests.

Second, as with many fish biology questions, this one peaked my interest and I did a quick internet search on anchor worms for a little more information.  The following three I found to useful, as most were aquarium oriented, Wikipedia, NAS - Nonindigenous Aquatic Species, and Animal Diversity Web.

Blog content © David Coulson
Blog Comments
Coyute, CO   11/7/2013 9:11:15 AM
Thanks for the info.
team FMFO , CO   11/7/2013 9:50:10 AM
Good info as I like to Ice Dowdy in the winter.
opencage, CO   11/8/2013 10:20:39 AM
Thanks for sharing the info Dave. Good to know it isn't hurting the fish or fishery. And another thanks to CPW and its workers for their info and efforts.