Optimizing Triploid Walleye Production in Colorado

Walleye (Sander vitreus) provide important recreational and commercial fisheries throughout the United States and Canada. In Colorado, more walleye are stocked every year than any other species of fish. Use of sterile triploid fish in Colorado is an important management strategy for protecting native endangered fish species from naturally reproducing populations of introduced predators like walleye. Triploid fish are created by exposing eggs to hydrostatic pressure shock, temperature shock, or chemical treatments after fertilization to prevent the extrusion of the second polar body. This results in sterile triploids because chromosomes are unable to synapse correctly during division. Hydrostatic pressure has been one of the more effective methods for inducing triploidy in walleye, and the technique is currently evolving. A 2.7-L capacity electric pressure chamber manufactured by TRC Hydraulics was used to produce triploid walleyes using hydrostatic pressure with eggs collected from Pueblo Reservoir, Colorado. The TRC hydraulic press has many advantages over manually-operated pressure chambers used to produce triploid fish including its portability, large capacity, safety, and increases in hatching survival and induction rates. Here, the methods used to create triploid walleye using the TRC hydraulic press are described. In addition, times to initiation (TIs; time between fertilization to when eggs were subjected to pressure) were varied between 4 minutes and 8.5 minutes to determine the optimal TI for maximizing induction and hatching success rates. Our results suggest that triploidy in walleye is maximized with a TI of approximately 7.5 minutes, whereas hatching success is maximized with a TI of just over 8 minutes. Because the goal of the triploid walleye production program in Colorado is focused on maximizing induction rates, we recommend inducing triploidy at approximately 7.5 minutes to meet this objective.