Publication Abstract

Plasma gonadotropin II, sex steroids, and thyroid hormones in wild striped bass (Morone saxatilis) during spermiation and final oocyte maturation

Plasma gonadotropin II, sex steroids,and thyroid hormones in wild striped bass (Morone saxatilis) during spermiationand final oocyte maturation

C.C. Mylonas, A.P. Scott, S.P. Minkkinen, B.M. Richardson and Y. Zohar The blood levels of gonadotropin II (GtH II),sex-steroid hormones, and thyroid hormones were determined in wild spermiating malestriped bass (Morone saxatilis) in males and in females at various stages of finaloocyte maturation (FOM), captured on their spawning grounds. The progression of spermiation was associated with increases in plasma GtH II and decreases in plasmatestosterone (T), 11-ketotestosterone, and thyroxine (T4). Plasma triiodothyronine (T3)remained at high and relatively unchanged levels. Plasma levels of 17,20β-dihydroxy-4-pregnen-3-one(17,20β-P) and17,20β,21trihydroxy-4-pregnen-3-one(17,20β,21-P), theproposed maturation-inducing steroids (MIS) in striped bass, were low and unchanged duringthe same period. It was concluded that low progestogen levels are adequate to inducespermiation in striped bass, and that higher levels may be associated with spawningbehavior. In the females, based on the profiles of the studied hormones, FOM was separatedinto two phases. Early FOM, which included germinal vesicle (GV) migration andlipiddroplet coalescence, was associated with elevations in plasma GtH II, T, andestradiol 173. Late FOM, which included GV breakdown and yolk-globule coalescence, wasassociated with a further surge in plasma GtH II, increases in the levels of the two MIS,mainly 17,20β-P,and a drop in T., Plasma T3 levels did not change during FOM. Examination of conjugatedsteroids demonstrated, in the males, a reduction in conjugated androgens at the peak ofthe spawning season and, in the females, a small increase in conjugated 17,20β-dihydroxylated and 5β reduced,3α-hydroxylated steroids after spawning.This is the most comprehensive report, to date, on the endocrine regulation of gonadalmaturation in wild striped bass, demonstrating that a two-stage process of FOM isregulated by different endocrine signals, providing further evidence for the involvementof 17,20β-P as aMIS in the females, and indicating that both males and females are in an euthyroid stateduring the spawning.

Reference:

C.C. Mylonas, A.P. Scott, S.P. Minkkinen, B.M. Richardson and Y. Zohar, 1997. Plasmagonadotropin II, sex steroids, and thyroid hormones in wild striped bass (Moronesaxatilis) during spermiation and final oocyte maturation. General and ComparativeEndocrinology, 108: 223-236.

C.C. Mylonas, A.P. Scott*, S.P. Minkkinen, B.M. Richardson and Y. Zohar

General and Comparative Endocrinology, 108: 223-236