The secret lives of triploid trout

A new study seeks to understand how trout live — and die — in dozens of Western Washington lakes, and the angling public can help.

An acoustically tagged rainbow trout post-surgery.

Just in time for the statewide lowland lakes opener and the beginning of trout season, the Washington Department of Fish and Wildlife (WDFW) is conducting a first-of-its-kind study to evaluate the movement and behavior of triploid and diploid rainbow trout in 29 Western Washington lakes — and we’re asking for help from the angling public.

Triploid trout — so called because they have three sets of chromosomes instead of the normal two (diploid) — are sterile fish that WDFW stocks in some lakes to help reduce interaction with native species living in the same waters. (You can learn more about how WDFW grows triploid trout at our previous blog post).

Many anglers think triploid trout grow to be larger than other trout, because they are less focused on the need to reproduce. But while some stocked triploids are larger than the average hatchery-grown rainbow when they’re planted into Washington lakes, the differences in growth, catch rates and behavior as their diploid counterparts is not well understood, said James Losee, Fish Program manager for WDFW’s Coastal region.

If you catch a trout with stitches in its stomach, it likely contains an acoustic telemetry tag. You can call 360–280–1762 for information on how to return the tag.

Losee is helping lead a research project to evaluate catch rates, movement patterns, and mortality rates of triploid trout in lakes throughout the region, and if you fish one of the lakes included in the study (see the full list at the bottom of this article), you may be able to help.

“Opening day is April 24, which is when fishing effort peaks in many lakes across the state” Losee said. “It also presents a great opportunity for the angling public to contribute to an important science effort that helps us better understand the benefits of triploid trout in these areas, and improve future fishing opportunities.”

Catch a fish? Report it!

The main way anglers can help is by catching trout, looking for adipose fins on their rainbow trout and reporting their results.

Anyone fishing in one of the study lakes can go online to report their catch using this online tool. If you catch one or more trout, let us know if each one has a clipped or unclipped adipose fin. If the fish has no adipose fin (clipped) it is a triploid. If the fish has an adipose fin (unclipped) it is a diploid.

The study will examine about 70,000 diploid trout and 65,000 triploid trout stocked in lakes across five Washington counties.

Report your catch here.

Find a tag? Return it!

An acoustic tag. Other tags may be even smaller than these, and we’re asking anglers to return any they find.

In addition, a select number of trout will be equipped with acoustic tags, which will allow researchers to monitor the trout’s movement within lakes, right down to when it’s caught and taken out via the boat ramp, or if it dies of natural causes or by predation, Losee said. The tags also track temperature of the surrounding waters, which researchers will use to monitor how the lake environment affects movement and natural mortality.

“If you catch a trout and it has stitches in its belly, or you cut into it and find a small black tag, we want to know about it,” Losee said. “We’re also asking anglers to return the uniquely numbered tags so we can identify exactly which fish was caught.”

Anglers who find a tag can call 360–280–1762 for information on how to return the tag.

Lakes included in the study:

Pierce County

  • Jackson Lake
  • Crescent Lake
  • Rapjohn Lake
  • Harts Lake
  • Clear Lake
  • Ohop Lake

Thurston County

  • Deep Lake
  • Ward Lake
  • McIntosh Lake
  • Clear Lake
  • Hicks Lake
  • Pattison Lake

Jefferson County

  • Silent Lake
  • Tarboo Lake

Kitsap County

  • Buck Lake
  • Haven
  • Horseshoe Lake
  • Mission Lake
  • Panther Lake
  • Wildcat Lake

Mason County

  • Aldrich Lake
  • Benson Lake
  • Don Lake (Clara Lake)
  • Devereaux Lake
  • Lake Limerick
  • Magee Lake
  • Robbins Lake
  • Tiger Lake
  • Wooten Lake



The Washington Department of Fish and Wildlife

The Washington Department of Fish and Wildlife is dedicated to preserving, protecting and perpetuating the state’s fish and wildlife resources.