Understanding and Managing Gill Lice Infections in Reservoir Sport Fish

Led By

Lake and Reservoir Researchers

Study Area

Select reservoirs

Project Status

Ongoing

Research Objectives

• Monitor gill lice infection prevalence and intensity on kokanee salmon and rainbow trout populations in key reservoirs in relation to environmental conditions to identify factors contributing to high parasite burdens and potential mitigation strategies.

Project Description

Gill lice, parasitic copepods (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 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 very difficult to control. Further, very little research has been conducted on gill lice, making management challenging.​

Lake and Reservoir Researchers have been monitoring gill lice infestations within kokanee and rainbow trout populations in select reservoirs to better understand how different factors such as the density of vulnerable fish, environmental conditions, and water level fluctuations interact to influence parasite burdens.

With a greater understanding of gill lice dynamics, we may be able to identify management strategies that effectively limit infection prevalence and intensity.

Associated Publications

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

Lepak, J.M., A.G. Hansen, M.B. Hooten, D. Brauch, and E.M. Vigil. 2022. Rapid proliferation of the parasitic copepod Salmincola californiensis (Dana) on kokanee salmon, Oncorhynchus nerka (Walbaum), in a large Colorado reservoir. Journal of Fish Diseases 45:89-98 (Cover image and story for journal issue).

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.