UW Researchers Investigate Possible Rapid Evolution Of Stocked Fish

Jun 19, 2019

The lakes in the alpine areas of the Wind River Range have historically been fishless - that is, until humans started stocking them for recreational use. The introduction of these fish changed the ecosystems of the lakes, and specifically, the microscopic animals that float through the water, known as zooplankton. Now, University of Wyoming researchers want to know if the change in zooplankton has influenced a change in the fish.

Catherine Wagner, a professor in the department of botany at UW, is trekking to the backcountry to learn about the changes these trout may be experiencing. She will be collaborating on this project with two UW zoology professors, Annika Walters and Amy Krist, and a UW geology professor, Bryan Shuman.

Zooplankton in fishless lakes are large and easy to see.
Credit Catherine Wagner

Previous research by Wagner, Walters and Krist has shown that zooplankton in stocked lakes, which are eaten by the fish, are now smaller than they were before stocking. Now they want to know if the change in these plankton has influenced any change in the fish that eat them.

"They eat the large and easily visible plankton in the system, and that leaves them in lakes without large and easily visible plankton to eat," Wagner said.

Even though the zooplankton have decreased in size and become harder to see, the fish have persisted in the lakes. Wagner thinks that this may have something to do with a change in the fish's overall structure.

"Fish have gills that help them breathe. They also have rakers on the other side of the part of the gill that help them breathe which act like a sieve to keep the food that they're eating from just passing directly out the gills after they've taken a swallow of water," Wagner explained. "And so we think that we're going to see a response so that the rakers become more finely spaced so that they can eat smaller food items more effectively."

UW's research team will compare the structures of lake fish to those of hatchery fish to detect any differences. If these structural changes have taken place, there is strong evidence for rapid evolution in these fish. They will also be looking for possible hybridization between the two types of trout in the lakes. Sediment cores taken from the lake will provide additional evidence if there has been a change in the ecosystem.

The findings of this research could influence future management and stocking decisions. If there is evidence of self-sustaining populations in these remote lakes, there may be a decrease in future restocking of them, and the research may be repeated in other remote lakes for similar management decision.