The Israeli Journal of Aquaculture - Bamidgeh 54(2), 2002
The Annual Dan Popper Symposium


THE INFLUENCE OF PHYTOESTROGENS AND ESTRADIOL-17ß
ON GROWTH RATES AND SEX DETERMINATION
IN THE EUROPEAN EEL (ANGUILLA ANGUILLA)


Itai Tzchori¹,² *, Gad Degani²,³ , Ronit Elisha² , Rivka Eliyahu² , Avshalom Hurvitz² , Jacob Vaya² , Boaz Moav¹

1 Department of Zoology, Tel Aviv University, Tel Aviv 69978, Israel
2 MIGAL, Galilee Technological Center, Kiryat Shmona 10200, Israel
3 School of Science and Technology, Tel Hai Academic College, Israel


Abstract

The ratio between males and females of the European eel (Anguilla anguilla) raised in different environmental conditions seems to vary. In commercial aquaculture, the majority of European eels (raised from glass eels) develop male gonads, whereas females reach a higher weight and greater market value. To test the effect of estrogen on growth rate and sex determination, the following experiments were conducted: juvenile European eels (0.4-0.6 g) with undifferentiated gonads were fed a diet supplemented with estradiol-17ß (E2) or phytoestrogens for 100-150 days. Treatment with estradiol-17ß resulted in an average body weight that was 50-61% higher than in the control groups. Estradiol and phytoestrogens significantly enhanced the percentage of females in eels. While the control group produced only 5-7% females, treatment with estradiol at 20 mg/kg resulted in 70% females and treatment at 2 mg/kg estradiol resulted in 30% females after 100 days of treatment. Treatment with estradiol at 10 mg/kg for 150 days instead of 100 days resulted in about 90% females. Soy extract 1 groups had a high percentage of females (55%) at 2 mg/kg but, at a higher dose of 20 mg/kg, the percentage of females decreased to 15%. Soy extract 2 and licorice, each at 20 mg/kg, resulted in 30% and 18% females, respectively, also significantly higher than the control group. Our preliminary results demonstrate that phytoestrogens can be used as an alternative to sex steroids for sex manipulation in eels.

*Corresponding author: E-mail: tzchori@post.tau.ac.il

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