Estrogens and estrogenic effects in Tilapia aurea (Cichlidae, Teleostei)

Estradiol (E₂) level in plasma of non-breeding female Tilapia aurea, measured by RIA, was 0.33 ± 0.02 ng/ml (mean ± SEM, n=6). This level is about 10% of the level found in breeding females, about 4 times higher than in ovariectomized females and similar to the level found in non-breeding males. Twenty-four hours following a single i.p. injection of 0.5 mg E₂, the estradiol level in plasma of ovariectomized Tilapia was within the physiological range (0.2-10 ng/ml). This level was maintained for at least 4 days. Comparison of the vitellogenic potency of 3 estrogens in ovariectomized T. aurea shows that estriol was more potent than estradiol, which, in turn, was more potent than estrone. Since E₂ increased in the plasma of estrone-injected fish, it is assumed that estrone was converted to estradiol in the recipient fish.