Endocrine changes during natural spawning in the white sucker, Catostomus commersoni. II. Steroid hormones.

Blood samples were taken from white suckers (Catostomus commersoni) during their annual spring spawning migration and analyzed by radioimmunoassay for gonadotropin (GtH), estradiol-17 beta (E2), testosterone (T), 11-ketotestosterone (11-KT), 17 alpha-hydroxyprogesterone (17-P), 17 alpha-hydroxy-20 beta-dihydroprogesterone (17, 20-P), androstenedione (A), and cortisol. GtH, 17-P, and 17,20-P levels were low in prespawning fish of both sexes, rose to their highest levels in ovulated females and spawning males, and then fell to low levels in spent fish. In females, E2, T, and A levels were high in prespawning fish and declined significantly at ovulation, dropping to lowest levels in spent fish. In males, 11-KT, T, and A levels were highest in prespawning fish, and lowest in spent fish. Cortisol levels were highest in spermiating males and ovulated females. Plasma profiles of the sex steroids in the white sucker are very similar to those observed in the rainbow trout (Salmo gairdneri).