Post-Stocking Performance of Triploid Walleye

Post-Stocking Performance of Triploid Walleye

​​​​​​​​Led By

Lake and Reservoir Researchers and Colorado State University (CSU)

Study Area

Select reservoirs

Project Status

Ongoing

Research Objectives

• Measure the post-stocking feeding, growth and survival of sterile walleye relative to their non-sterile counterparts.
• Determine the most appropriate stocking procedures for sterile walleye.
• Evaluate the potential for sterile walleye to interfere with unwanted natural reproduction.

Project Description

​Every spring CPW collects eggs from wild populations of walleye to raise in the hatchery and stock back out into reservoirs to supplement fisheries. Some of these eggs are specially treated to produce “triploids”. Triploidy is induced by placing fertilized eggs into a hydrostatic pressure chamber. As a result, the fry that hatch retain an extra set of chromosomes (unlike their normal “diploid” counterparts), rendering them incapable of naturally-reproducing over their lifespan. Because triploid walleye are sterile, they can be stocked to support sport fisheries in strategic locations where natural walleye reproduction is not wanted.

Interest in triploid walleye as a management tool is increasing. However, little is known about their post-stocking performance. Understanding post-stocking performance helps identify best stocking practices and calibrate expectations on potential fishery quality. CPW researchers along with collaborators from CSU have been examining numerous aspects of triploid walleye ecology, including how well they grow and survive after being stocked, the types of prey they eat, their uptake of contaminants like mercury, and potential to interfere with unwanted natural reproduction.

General findings to date indicate that triploids eat and grow similarly to diploids, but do not survive as well early in life, which could potentially be overcome by stocking larger fingerlings rather than fry. Both triploid males and females of mature age exhibited negligible development of reproductive tissues. This was expected for females, but not males, suggesting that the ability of triploid males to interfere with unwanted natural reproduction may be relatively low. However, limited development of reproductive tissues contributed to lower mercury levels in triploid fish compared to diploids, making them safer to eat. Research on triploid walleye is ongoing, but they represent a promising management tool for providing desirable sport fisheries in sensitive locations where natural reproduction is not wanted for purposes of native fish protection or other management objectives. 

Associated Publications

Farrell, C.J., A.G. Hansen, M.M. Brandt, C.M. Myrick, B.M. Johnson. 2024. An evaluation of the relative size, condition, and apparent survival of triploid walleye in the wild. North American Journal of Fisheries Management 44:172-188.

Farrell, C.J., B.M. Johnson, A.G. Hansen, and C.M. Myrick. 2022. Induced triploidy reduces mercury bioaccumulation in a piscivorous fish. Canadian Journal of Fisheries and Aquatic Sciences 79:202-212 (Received Editor’s Choice Award).

Farrell, C.J., B.M. Johnson, A.G. Hansen, C.A. Myrick, E.C. Anderson, T.A. Delomas, A.D. Schreier, and J.P. Van Enennaam. 2022. Cytological and molecular approaches for ploidy determination: results from a wild walleye population. North American Journal of Fisheries Management 42:849-856.

Farrell, C.J., B.M. Johnson, A.G. Hansen, B. Avila, and C.M. Myrick. In revision. Does reproduction cause growth deceleration? Induced sterility illuminates the effects of reproduction of growth. Canadian Journal of Fisheries and Aquatic Sciences.

Hansen, A.G., C.J. Farrell, and B.M. Johnson. 2023. Simulated effects of imperfect sterile sport fish stocking on persistence of fertile fish in new exploited populations. North American Journal of Fisheries Management 43:908-934.