Colorado Parks and Wildlife

Led By

Dr. Eric R. Fetherman

Study Area

Colorado River, Poudre River, and South Platte River Drainages

Project Status

Ongoing

Research Objectives

To evaluate the stocking success of whirling disease resistant rainbow trout in the Colorado River.

Project Description

Whirling disease caused severe declines in rainbow trout populations across Colorado following its introduction in the 1980s. One promising approach for the recovery of Colorado’s rainbow trout populations has been the production of rainbow trout strains that are genetically resistant to the parasite that causes whirling disease, Myxobolus cerebralis.

Many of the state’s rivers have already been stocked with these strains. However, much of the research on the success of these stockings has been focused on the Colorado River below Windy Gap Reservoir in Grand County.

Here, stocking shows promising results. Through yearly spring electrofishing efforts, researchers can estimate the population size, growth, and survival of adult resistant rainbow trout stocked in the upper Colorado River in 2006, 2009 and 2010, and rainbow trout fry stocked in 2013 through 2016. Results suggest that the stocked rainbow trout have survived and reproduced in the river. As the presence of resistant rainbow trout has increased, researchers have observed decreases in infection severity in young rainbow trout. This could ultimately lead to a reduction in overall infection levels in the upper Colorado River over time. Stocking rainbow trout as fry has also shown promise, with stocked rainbow trout recruiting to the adult population. This has resulted in an increase in the number of adult rainbow trout present in this section of the Colorado River in recent years. Fry stocking and monitoring the success of these stockings will continue in the Colorado River in the years to come.

In 2014, two different strains of whirling disease resistant rainbow trout were stocked as fry in nine streams, three in each of the Colorado River, Poudre River, and South Platte River drainages as part of a Colorado State University master’s project. The objective was to determine if one of the strains would be better used for fry stocking than the other based on survival and growth in these different locations. Overall, research suggested that both strains exhibited similar survival rates in these streams. As such, depending on the severity of infection and management goals for a specific water, both strains could be used for stocking purposes when stocked as fry.

This is a collaborative project between Colorado Parks and Wildlife and Colorado State University.