Meiotic gynogenesis induction in muskellunge Esox masquinongy by thermal and pressure shocks

Mass production of fast-growing, all-female muskellunge Esox masquinongy by gynogenesis requires optimized techniques of preventing second polar body extrusion. Heat, cold, and pressure shocks were evaluated for their efficiency of doubling the maternal genome. Muskellunge eggs (20-40 g) were activated with 1 mL ultraviolet (UV)-irradiated (1,248 J/ m(2)) heterologous sperm of yellow perch Perca flavescens. Survival and ploidy (by flow cytometry) were determined during the eyed-stage. Cold shocks of 1.3 +/- 1 C were applied at 5 or 20 min after gamete activation with water (time of initiation, TI) for a duration of 150 min and pressure shocks of 48,263 or 55,158 kPa (7,000 or 8,000 psi, respectively) at a TI of 4 min for 12 min. These shock treatments resulted in 43.7-95.0% diploid gynogens with corresponding yield of diploid gynogen (percent diploid gynogens X total percent survival) of 2.6-11.1%. Cold shocks applied at TI of 5 or 20 min after activation resulted in statistically similar percent survival, percent diploid gynogens, and yield of diploid gynogens. Heat shocks of 31 +/- 0.1 C applied at a TI of 5 to 15 min for a duration of 5 min resulted in 4.8-21.1% diploid gynogens with yields of 0.1-0.4%. Cold and pressure shocks have better potential than heat shock for preventing the second polar body extrusion. Muskellunge eggs activated with UV-irradiated yellow perch sperm, but not exposed to shock, resulted in 100% haploids with survival of 2.3-5.8%. No viable embryos were produced from the hybrid cross between muskellunge and yellow perch, thus, all diploids produced after the shock treatments were unambiguous meiotic gynogens. Muskellunge eggs fertilized with fresh muskellunge sperm (controls) showed 60.4-64.0% survival to the eyed-stage and 100% diploidy. Considering that the sex-determining mechanism in muskellunge follows the WZ female, ZZ male system, future efforts should be directed to test the efficiency of cold and pressure shocks for mass-producing gynogenetic super female (WW) muskellunge.