SEASONAL ENDOCRINE CHANGES IN MALE AND FEMALE ARCTIC CHARR (SALVELINUS-ALPINUS) .1. PLASMA-LEVELS OF 3 ANDROGENS, 17-ALPHA-HYDROXY-20-BETA-DIHYDROPROGESTERONE, AND 17-BETA-ESTRADIOL

Plasma levels of the androgens testosterone (T), 11-ketotestosterone ( OT), and 11-ketoandrostenedione (OA), the progestin 17-alpha-hydroxy-2 0-beta-dihydroprogesterone (17,20-P), and 17-beta-estradiol (E2) were measured by radioimmunoassay over the annual cycle in both adult male and female Arctic charr (Salvelinus alpinus). In both males and female s plasma T, OT, and OA all reached their highest levels during the ear ly breeding season in September. The dominant androgen in maturing mal es was OT, which reached levels of ca. 90 ng/mL. Plasma levels of OT a nd OA, but not T, were considerably higher in males than in females; 1 7,20-P peaked later than the androgens, in November in males (14 ng/mL ) and October in females (0.8 ng/mL). E2 was always low or nondetectab le in males. In maturing females E2 peaked in August (3.5 ng/mL) befor e falling concomitantly with rising T levels. From January to April pl asma levels of all measured steroids were low in both males and female s.