Abstract
We evaluated heat shocks and hydrostatic pressure shocks as methods of manipulating ploidy in walleyes Stizostedion vitreum. Hydrostatic pressure shocks of 8,000 psi (1 psi = 6.895 kPa) applied at 4 min postfertilization (i.e., time of initiation, TI) for 30 min produced 100% triploidy in eggs from 18 of 20 females, survival ranging from 50% to 80%. At a preshock incubation temperature of 11°C, heat shocks of 28–31°C applied at a TI of 1–5 min postfertilization for 25 min induced triploidy in 20–50% of the shocked eggs and resulted in embryonic survivals of 20–50%. Hydrostatic pressure shock offered several advantages over heat shock as a method of inducing triploidy in walleyes. Hydrostatic pressure shock of 9,000 psi applied at a TI of 192 min for 8 min was most effective for inducing tetraploidy in walleyes. To date, however, no walleye tetraploids have survived beyond the sac-fry stage.