The Science of Spawning Triploid Trout

Manual spawning of rainbow trout takes place every fall at the Spokane Hatchery, to ensure future generations of the fish are available to stock area lakes the following spring. It’s a wet job, with volunteers from across the agency getting together several times throughout November and December to spawn thousands of trout. And while it’s a lot of work, it results in some great fisheries throughout eastern Washington.

This video shows the steps involved in manually spawning trout.

Also, on spawning days each fall, WDFW staff use some of the eggs and milt (sperm from the male fish) gathered to create triploid trout to also be planted in Washington lakes and rivers.

Triploid trout have three complete sets of chromosomes instead of two, which causes them to be infertile. The DNA in triploid trout is not modified or edited. What else is triploid? Bananas and seedless watermelon!

Stocking triploid trout allows WDFW to offer trout fisheries that do not impact native fish. For example, WDFW plants triploids in Lake Spokane- also known as Long Lake- so that the naturally occurring redband rainbow trout are not affected but anglers still have the opportunity to harvest fish. Triploid trout fry are also planted into Lake Roosevelt net pens. WDFW is required to only plant triploid rainbow trout in any lake in Pend Oreille County to protect the native westslope cutthroat and bull trout.

WDFW fish managers often get requests from the public to stock more triploids, believing that triploid trout grow larger, since they are putting all their energy toward growth and not reproduction. In eastern Washington, diploid trout grow equally as well as triploid fish. The use of triploid trout is for conservation of wild fish in some areas of the state and not for the improved growth of stocked fish.

There are a few methods available to produce triploid trout. As the video shows, WDFW uses the heat-shock method that warms just-fertilized eggs to retain a normally expelled chromosome, creating the sterile triploid. After the warm water bath, the fertilized eggs are placed back into the 50-degree spring water that feeds the Spokane Hatchery for a couple of weeks to continue to develop. Right around 16 days after fertilization, eyes start to develop on the eggs. This is the sign that it is time to movesome of the fish ato other hatcheries to be reared. The rest stay at the Spokane Hatchery to finish growing until they can be released into area lakes and rivers.

This is one example of how WDFW hatcheries and fish program managers work together to produce fish that meet conservation and sport fishing goals.