ISU Headlines

ISU study confirms rainbow trout are stronger than cutthroat

Posted January 25, 2008

Idaho State University researchers have discovered what sport fishermen have long suspected when they have hooked and are reeling in a trout: native cutthroat trout, a declining species, just aren’t as strong competitors as nonnative rainbow trout.

Snake River cutthroatRecent ISU doctoral graduate Steven Seiler and biological sciences professor Ernest Keeley measured the difference in the swimming stamina of cutthroat trout versus rainbows and cutthroat-rainbow hybrids. The researchers raised Yellowstone cutthroat trout, rainbows and hybrids of the two species and tested their stamina by putting them in small tubes filled with water. They controlled the power of the water flowing through the tubes and measured the results.

“Our results suggest that introduced rainbow trout and cutthroat-rainbow trout hybrids can potentially out-compete native Yellowstone cutthroat trout through higher sustained swimming ability,” Keeley said.

Besides being stronger, the shape of the rainbow trout’s fins and body are more efficiently designed for swimming.

Keeley’s and Seiler’s study is a one of a broad range of studies (please see related story) by researchers at a variety of institutions to determine how to protect native cutthroat trout species. In waters where rainbow trout have been introduced, the rainbows and hybrids are thought to have eliminated, threatened or weakened native cutthroat populations by being dominant genetically when the fish interbreed. Rainbows are also proving to be hardier fish.

In another study, Keeley and Seiler found that rainbows and hybrids had the highest success over cutthroat of occupying and inhabiting the areas of streams that offer the best feeding opportunities. This study suggests, “juvenile Yellowstone cutthroat trout are less successful at maintaining profitable feeding territories and capturing food items when competing against rainbow trout and first generation hybrids.”

The studies mentioned are posted at The titles of studies appearing in this article are:

    • Seiler, S.M. and Keeley, E.R. 2007. A comparison of aggressive and foraging behavior between juvenile cutthroat trout, rainbow trout, and F1 hybrids. Animal Behaviour, 74: 1805-1812.

•  Seiler, S.M. and Keeley, E.R. 2007. Morphological and swimming stamina differences between Yellowstone cutthroat trout (Oncorhynchus clarkii bouvieri), rainbow trout (Oncorhynchus mykiss), and their hybrids. Canadian Journal of Fisheries and Aquatic Sciences 64:127-135.

Photo provided by Dr. Ernest Keeley