Seasonal endocrine changes in male and female Arctic charr (Salvelinus alpinus). I. Plasma levels of three androgens, 17α-hydroxy-20β-dihydroprogesterone, and 17β-estradiol

Plasma levels of the androgens testosterone (T), 11-ketotestosterone (OT), and 11-ketoandrostenedione (OA), the progestin 17α-hydroxy-20β-dihydroprogesterone (17,20-P), and 17β-estradiol (E 2 ) were measured by radioimmunoassay over the annual cycle in both adult male and female Arctic charr (Salvelinus alpinus). In both males and females plasma T, OT, and OA all reached their highest levels during the early breeding season in September. The dominant androgen in maturing males was OT, which reached levels of ca. 90 ng/mL. Plasma levels of OT and OA, but not T, were considerably higher in males than in females; 17,20-P peaked later than the androgens, in November in males (14 ng/mL) and October in females (0.8 ng/mL). E 2 was always low or nondetectable in males. In maturing females E 2 peaked in August (3.5 ng/mL) before falling concomitantly with rising T levels. From January to April plasma levels of all measured steroids were low in both males and females.