The effects of 17β-estradiol on various reproductive parameters in the hermaphrodite fish Kryptolebias marmoratus

The effect of a single injection of 17β-estradiol (E2) was evaluated in the hermaphrodite fish Kryptolebias marmoratus. The fish [average body weight (BW), 0.15 ± 0.01 g] were injected with either two concentrations of E2 (1 and 100 μg/g BW) once intraperitoneally. They were sampled at intervals of 7, 15, and 30 days after a single E2 injection. Gonadosomatic index (GSI), hepatosomatic index (HSI), the frequency of gonadal development, number of ovulated eggs, and plasma steroids levels were measured. The transcript abundances of vitellogenin (VTG) and estrogen receptors (ERα and β) mRNA in the liver were also analyzed using quantitative real time polymerase chain reaction (real time PCR). GSI and the frequency of mature oocytes in the 100-μg E2-exposed group decreased compared to that of the control group during the experiment, and the number of ovulated eggs in the 100-μg E2-exposed group was lower when compared to the other groups. However, plasma E2 and 11-ketotestosterone (11-KT) levels were not significantly different between the experimental groups. On the other hand, plasma testosterone level and VTG mRNA abundance in the 100-μg E2-exposed group were significantly lower than the control group after 30 days. These results indicate that E2 stimulation at high concentration interferes with reproductive phenomena through delayed response. In addition, HSI in the 100-μg E2-exposed group and ERα mRNA abundance in the 1-μg E2-exposed group were significantly higher than the control group at 7 days after E2 injection, although there was no significant difference in HSI and ERα mRNA between all groups at 30 days. These results indicate temporal responses in reproductive parameters following high-dose E2 exposure in the hermaphrodite fish K. marmoratus.