Endocrine regulation and artificial induction of oocyte maturation and spermiation in basses of the genus Morone

Abstract

Studying the process of final oocyte maturation (FOM) and spermiation in striped bass ( Morone saxatilis), it was determined that the failure to undergo FOM and produce normal amounts of milt in captivity was due to low plasma levels of luteinizing hormone (LH) during the spawning period. As a result, the expected changes in the plasma profiles of the steroids involved in FOM and spermiation do not take place. Based on the hormone profiles and the associated histological examinations, FOM can be separated into an early phase (germinal vesicle (gv) migration) and a late phase (germinal vesicle breakdown). The progestogen 17,20β,21-trihydroxy-4-pregnen-3-one (17,20β,21-P) was identified as the maturation-inducing steroid (MIS), but the high levels of 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) present during late FOM, suggest a role for this steroid also. In wild striped bass, spermiation was associated with increases in LH and unchanged plasma levels of 17,20β,21-P and 17, 20β-P. In culture, spermiation in both striped bass and white bass ( M. chrysops) proceeds under undetectable levels of LH, 17,20β,21-P and 17,20β-P. GnRHa-induced spermiation, however, was associated with increases in plasma LH and 17,20β-P, but not 17,20β,21-P. Treatment of females with GnRHa-delivery systems induced long-term increases in plasma LH and the appropriate changes in sex-steroid hormones. In white bass, GnRHa-delivery systems induced two successive spawns within 3 days from treatment, and in a commercial production facility induced ovulation of 90% of the females, producing 294,500 eggs kg −1 with 81% fertilization. Similarly treated striped bass underwent FOM and ovulation within 10 days after treatment, while tank spawning resulted in the production of 170,000 eggs kg −1 with 47% fertilization success. In male fish, GnRHa-delivery systems induced significant elevations of expressible milt for up to 20 days, resulting in a fourfold increase in production of spermatozoa, without affecting sperm density, motility or fertilization %.