Serum levels of 11-oxotestosterone in male and 17 beta-estradiol in female rainbow trout (Salmo gairdneri) during the first reproductive cycle.

From September 1980 to August 1981 the serum levels of 11-oxotestosterone (11-O-T) in 231 male and of 17 beta-estradiol (E2) in 207 female rainbow trout were measured radioimmunologically, and compared with the development stages of the gonads. Using histological criteria, testicular development was divided into seven stages, and ovarian development into four stages. In males, 11-O-T levels remained below 6 ng/ml until the appearance of spermatozoa. Maximum values (126 ng/ml) were observed in spermiating males. In females, E2 levels were below 2 ng/ml during the period of slow oocyte growth. Maximum values (average of 31 ng/ml) were observed during exogenous vitellogenesis.