ENDOCRINE PROFILES OF FEMALE STRIPED BASS (MORONE-SAXATILIS) IN CAPTIVITY, DURING POSTVITELLOGENESIS AND INDUCTION OF FINAL OOCYTE MATURATION VIA CONTROLLED-RELEASE GNRHA-DELIVERY SYSTEMS

Plasma levels of reproductive and thyroid hormones were measured in ca ptive striped bass females during postvitellogenesis and the spawning period (March-June). Circulating gonadotropin II (GtH IT), 17,20 beta- dihydroxy-4-pregnen-3-one (17,20 beta-P), and 17,20 beta,21-trihydroxy -4-pregnen-3-one (17,20 beta,21-P) remained low and unchanged in nonma turing females, while 17 beta-estradiol (E-2) and testosterone (T) dec lined throughout postvitellogenesis. Plasma thyroxine (T-4) declined s ignificantly in mid-April, while triiodothyronine (T-3) increased in m id-May, The only female that ovulated spontaneously had markedly diffe rent E-2, T, and T-3 profiles during postvitellogenesis, and had a sur ge in plasma GtH II during final oocyte maturation (FOM). The lack of a GtH IZ surge is presumably responsible for the absence of FOM, but e arlier, and as of yet unknown, endocrine disruptions during postvitell ogenesis may determine the female's ability to undergo FOM. Treatment of females with a gonadotropin-releasing hormone agonist (GnRHa)-deliv ery system induced FOM and ovulation within 3 and 10 days, respectivel y, and resulted in the production of fertile eggs. Plasma GtH II incre ased continually after GnRHa implantation, even in the presence of dec lining GnRHa plasma levels. Plasma E-2 increased first and peaked prio r to FOM, whereas T peaked at the peripheral germinal vesicle (GV) sta ge. Plasma 17,20 beta-P and 17,20 beta,21-P increased dramatically at the GV breakdown (GVBD) stage. Plasma T-4 was unaffected by the GnRHa treatment, whereas T-3 decreased after GnRHa implantation and remained low throughout FOM. Based on the observed hormonal profiles, FOM can be separated into an early phase (lipid-droplet coalescence, GV migrat ion) associated with E-2 and T elevations, and a late phase (yolk-glob ule coalescence, GVBD) associated with 17,20 eta-P and 17,20 beta,21-P elevation. (C) 1998 Academic Press.