Induction of gynogenesis in muskellunge with irradiated sperm of yellow perch proves diploid muskellunge male homogamety

Diploid gynogenesis was induced in muskellunge Esox masquinongy using UV-ir radiated muskellunge sperm as the first step in producing monosex females. In this approach, we have to rely on negative controls as an indirect refer ence for sperm genetic material destruction. In the first experiment, equal proportions of gynogenetic females and males were produced. Negative contr ols, UV-irradiated sperm without heat shock, yielded some normal hatching l arvae, described as spontaneous diploids. In the second experiment, muskell unge eggs were activated using sperm from yellow perch. Because hybrids bet ween these species are not viable, we produced unambiguous gynogens. When U V-irradiated yellow perch sperm was used to inseminate muskellunge eggs, ha ploids resulted (22.5% +/- 2.8% survival to the eyed stage). To produce dip loid gynogens, a heat shock of 31 degrees C was applied to inseminated eggs 20 min after activation for a duration of 6 min. This process yielded seve ral hundreds of gynogens for rearing. Several treatments of masculinizing h ormone, 17 alpha-methyltestosterone (MT), were carried out. Fish were disse cted and gonads examined histologically for sex determination. Gynogens pro duced using yellow-perch sperm confirmed the presence of males in the contr ol group, whereas the MT bath treatment (400 mu g/liter) resulted in the pr oduction of fish with ovotestis. These results provide evidence for male ho mogamety in muskellunge and imply that a change of strategy is needed to pr oduce monosex populations. (C) 2000 Wiley-Liss, Inc.