Manipulation of ploidy in walleyes by heat shock and hydrostatic pressure shock

We evaluated heat shocks and hydrostatic pressure shocks as methods of mani pulating ploidy in walleyes Stizostedion vitreum. Hydrostatic pressure shoc ks 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 incubatio n temperature of 11 degreesC, heat shocks of 28-31 degreesC 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 pr essure shock offered several advantages over heat shock as a method of indu cing 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 i n walleyes. To date, however, no walleye tetraploids have survived beyond t he sac-fry stage.