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Monday, September 1, 2014
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What Are Gill Lice?

Under Microscope

Gill lice Salmincola spp. are a parasitic copepod that only infect Salvelinus species such as brook trout Salvelinus fontinalis, which is the only salmonid native to Wisconsin streams. The gill lice life cycle begins when egg sacs release nauplii, which immediately molt into the larval first copepodid stage during which they have about 24 hours to find a host. The larval copepods anchor onto the gills of their host and continue development. After several molts, the copepods attain maturity and remain permanently attached to a gill arch.

For more information, download the Fact Sheet

How Do Gill Lice Impact Brook Trout?

Gill lice can cause significant physical trauma to the gill filaments, causing deformities that may affect respiration and efficient uptake of oxygen and release of carbon dioxide, ammonia, and other metabolites. Heavily infected brook trout cannot obtain sufficient oxygen when they are exercised, such as when caught by angling. Respiration may be particularly difficult for infected fish during times of high water temperatures and low dissolved oxygen levels. High rates of infection may slow the physiological processes of growth and sexual maturation, which in turn may negatively affect brook trout population growth rates. Gill lice are a parasite specific to brook trout and are not known to infect brown trout.

How Do You Observe Gill Lice?

Gill lice are readily observed on the gill arches of infected brook trout. To observe, hold the trout upside down in one hand and use your other hand to grab the upper jaw and gently flare open the gills. Gill lice, if present, will appear like white blobs hanging on the red gill filaments.

Brook Trout Without Gill Lice
Healthy brook trout without gill lice


Brook Trout With Gill Lice
Brook trout infected with gill lice

Agler-Based Monitoring of Gill Lice in Brook Trout Populations

Anecdotal observations of gill lice by anglers and Wisconsin DNR fisheries biologists suggest gill lice may be infecting more brook trout and spreading to more streams. However, we have little information on current and past distributions of gill lice in Wisconsin. We have implemented this web-based reporting system for anglers to use to document their observations of gill lice presence or absence on brook trout that they catch in streams, ponds, and lakes across Wisconsin.

How Can You Get Involved?

Participate in our angler-based monitoring program - Simply record your gill lice observations using our Online Survey. Alternatively, you can download a copy of our Offline Data Collection Form

Help Stop the Spread

It is becoming increasingly important in the battle against invasive species (not just gill lice) for anglers to become familiar with and follow proper disinfection practices - You can find more information in our Angler Disinfection Brochure

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Get Involved!

Participate in our angler-based monitoring program and record your gill lice observations using our Online Survey

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