SEX CONTROL AND PLOIDY MANIPULATIONS IN YELLOW PERCH (PERCA-FLAVESCENS) AND WALLEYE (STIZOSTEDION-VITREUM)

In both yellow perch (Perca flavescens) and walleye (Stizostedion vitr eum), females grow significantly faster and reach a larger ultimate si ze than males. In addition, reproductive development in both of these species can have a significant negative impact on somatic growth and f illet yield. Accordingly, methods for producing monosex female populat ions and for inducing sterility, have important potential applications for both commercial fish culture and fisheries management. Of the sev eral available methods for producing monosex female populations in fis hes (such as yellow perch and walleye) in which females are homogameti c, the preferred method (described herein) may be to treat juveniles w ith androgens to induce phenotypic sex inversion of genetic females, a nd to subsequently use sperm from these females to fertilize normal eg gs. Initial efforts at inducing sterility focused on the direct use of either heat or hydrostatic pressure shocks to produce triploid yellow perch and walleye. The gonadal development of triploid yellow perch a nd walleye of both sexes is retarded compared to that of diploids, and triploid yellow perch can have higher fillet yields than diploids. Th e direct use of heat and pressure shocks to induce triploidy in yellow perch, however, has negative effects on growth that are independent o f ploidy status. One way to circumvent this problem is to produce trip loids by crossing fertile tetraploids with diploids. To date, methods of producing viable tetraploids (beyond the larval stage) have been de veloped for yellow perch but not for walleye.