Sex Control of the Japanese Eel by an Estrogen(DES-Na) in Feed.

Abstract

The sex of the Japanese eel could be controlled by the oral administration of DES-Na (sodium diethylstilbestrol) which also promoted growth. Elvers were reared from glass eels for more than 500 days with a commercial feed which contained DES-Na (0 , 0.5, 0.75, 1.0 ppm).All the eels were dissected at the end of the experiment to check the sex by both external appearance and histological examinations of gonads.The sex groups were divided into male, male?, female, female? and unknown by their external appearance, and into male, female, hermaphrodite, and non-sex by histological examination.The largest discrepancy (27.5%) in the two examinations was found in the male: the histological examination was found to be essential.The female ratio increased along with an increase in DES-Na.It was 7.7% in the control and 23 .2-35.4% in DES-Na groups. The male ratio was 64.1% in the control and 32.0-40.4% in DES-Na groups.The hermaphrodite ratio was 1.1-4.6%, and the non-sexual ratio was 23.8-38.0%.Females were the largest of all sex groups. The growth promoting effect was found to vary with the growth stage.

Unusual Cases of Adult Intersexuality in the European Eel <b><i>Anguilla anguilla</i></b>

“…The proportion of AI eels was very low, representing 1.4% (2/140) of eels investigated at the microscopic level. This is comparable to what was found in A. japonica kept in similar conditions [Satoh et al, 1992]. These authors designed an experiment to assess the effect of an estrogen treatment on sex ratio and found 1.7% of hermaphrodite eels in the control group.…”

“…1978; Takahashi, 1979;Satoh et al, 1992;Lokman and Young, 1998]. The 2 AI European eels described in the present study were fortuitously identified during the course of a previous experiment aiming to compare aromatase gene expression between females, males and juvenile intersexual eels.…”

Sex Determination in Freshwater Eels and Management Options for Manipulation of Sex

“…For example, 17a-ethynylestradiol induced ovarian differentiation in 90% of 60-80 mm LT elvers, 65% of 150-180 mm yellow eels, and had only a moderate feminizing influence on 220-250 mm LT yellow eels (Colombo and Grandi, 1995). Oestrogens may also have a feminizing effect on older individuals with macroscopically differentiated gonads (Satoh et al, 1992). Increasing the dose (Degani and Kushnirov, 1992;Satoh et al, 1992;Tzchori et al, 2002) and the duration of exposure (Anderson et al, 1996;Tzchori et al, 2002) may also influence the final sex ratio in favor of females.…”

“…Female sex steroids, such as diethylstilbestrol, 17ß-estradiol and 17a-ethynylestradiol, stimulate the development of ovaries and can increase markedly the proportion of females produced (Table 2). In most cases feminization is accompanied by increased growth (Degani, 1986a;Satoh et al, 1992;Chiba et al, 1993;Anderson et al, 1996;Grandi et al, 2000;Tzchori et al, 2002;Degani et al, 2003). Naturally occurring plant hormones, phytoestrogens, may also have a significant feminizing effect (Tzchori et al, 2002).…”

“…Oestrogens may also have a feminizing effect on older individuals with macroscopically differentiated gonads (Satoh et al, 1992). Increasing the dose (Degani and Kushnirov, 1992;Satoh et al, 1992;Tzchori et al, 2002) and the duration of exposure (Anderson et al, 1996;Tzchori et al, 2002) may also influence the final sex ratio in favor of females. Male sex steroids such as 17a-methyltestosterone also increase individual growth rates (Degani, 1986ab), but have been shown to have only weak masculinizing effects.…”