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Understanding and Decreasing Gill Lice Infections in Colorado Fish
Understanding and Decreasing Gill Lice Infections in Colorado Fish

​​​​​​​​​​​​​​​​Led By

Estevan Vigil and George Schisler

Study Area


Project Status


Research Objectives

  • To understand the potential and current consequences of gill lice on economically and ecologically important fish.

  • To determine gill lice distribution in Colorado.​

Project Description

In Colorado, gill lice, a parasitic copepod (group of small crustaceans), can infect cutthroat trout, kokanee salmon and rainbow trout, which are ecologically and economically important fish species in Colorado. Gill lice are very host-specific, and thus far, only one species of gill lice (Salmincola californiensis) has been identified in Colorado.​

Gill lice attach to and damage the gills of the host fish, interfering with oxygen exchange. As a result, infections can negatively affect fish behavior, immune system function, growth, warm water tolerance and survival.

Fisheries managers are concerned about gill lice in Colorado because the parasite is resistant to chemical treatments and thus very difficult to control. Further, very little research has been conducted on gill lice, making management challenging.​

CPW initiated research to learn more about gill lice, specifically gill lice distribution in the state and the impacts of gill lice on Colorado's fish. Currently, CPW is the only agency conducting research on gill lice in Colorado and one of only a few in all of western North America.

With a greater understanding of gill lice, managers will be able to make management decisions that help protect and preserve Colorado's fish populations.​

Associated Publications

Vigil, E. M., K. R. Christianson, J. M. Lepak, and P. J. Williams. 2016. Temperature effects on hatching and viability of juvenile gill lice, Salmincola californiensis. Journal of Fish Diseases 39:899–905.  

Hargis, L.N., Lepak, J.M., Vigil, E.M., and Gunn, C. 2014. Prevalence and intensity of the parasitic copepod (Salmincola californiensis) on kokanee salmon (Oncorhynchus nerka) in a Colorado reservoir. Southwestern Naturalist 59(1):126-129. 2014.