The influence of phytoestrogens and oestradiol-17beta on growth and sex determination in the European eel (Anguilla anguilla)

Abstract

Under aquaculture conditions, European eels (Anguilla anguilla) produce a high percentage of males (809 5%) that normally stop growing at 100^200 g. Females continue to grow to 500^750 g and obtain higher market value. Therefore, increasing the percentage of females in a population would be bene¢cial to the culture of eels. The present study was carried out in order to examine the e¡ect of oestradiol and phytooestrogens on sex di¡erentiation and growth rate of eels. Juvenile European eels with undi¡erentiated gonads were fed pellets containing oestradiol-17b (E2) or phytooestrogens for 100^150 days. Feeding E2 resulted in 50^61% increase in body weight compared with the control. Oestradiol-17b and phytooestrogens both elevated signi¢cantly the percentage of females in the population. Feeding E2 at 20 mg kg À1 feed resulted in 70% females, while lower concentration of E2 (2 mg kg À1 ) resulted in only 30% after 100 days (Experiment 1). The same dose given for 150 days (Experiment 2) resulted in 88% females, indicating that both, the concentration and duration of E2 treatments had a signi¢cant e¡ect on sex di¡erentiation. Fish fed genistein at 2 mg kg À1 for 100 days, resulted in 55% of females, but at a higher dose of 20 mg kg À1 there were only15% females. These results demonstrate that phytooestrogens can be used as alternatives to gonadal steroids for sex manipulation in eels, but the optimal concentrations and duration are still to be determined.

A Model of Hormonal and Environmental Involvement in Growth and Sex Differentiation in European Eel (<i>Anguilla Anguilla</i>)

“…A high percentage (70%) of females was found among the European eels administered E 2 (60 mg/Kg diet) [20]. This result is supported by other studies [21], [31]. The hormone controlling the E 2 is FSH.…”

“…Cloned [17] cDNA of European eel and the RNA level of FSH were significantly higher than in males [32]. Moreover, the expression of aromatase (EeCYP19) gene during the process of sex determination in adult male gonads was lower when compared to the adult female group [21], [31].…”

“…In the model for the environmental effect on sex differentiation and growth (Figure 2), it is proposed that low density in the hypothalamus-pituitary-gonad axis is affected by high FSH [32] and gonad synthesis E 2 by EeCYP19, and E 2 affects gonad to ovary differentiation [21], [31]. Proposed model of the effect of environment and density on sex differentiation [2], [10], [11], [14], [19]- [21].…”

“…The effect of hormones on sex determination and growth by steroids [14], [19]- [21] was studied in detail.…”

INVESTIGATION OF GENETIC VARIABILITY IN THE EUROPEAN EEL (ANGUILLA ANGUILLA(L.)) IN LITHUANIA USING MICROSATELLITE DNA MARKERS

“…Meanwhile, the Japanese eels (Anguilla japonica) spawning ground appears to be in the west of the Mariana Islands in the North Pacific (Katoh & Kobayashi 2001;Tsukamoto & Arai 2001;Ringuet et al 2002;Tseng et al 2003;Tsukamoto 2006). Species of the Anguillidae family, especially the A. anguilla (Virbickas 2000;Hansen et al 2001;Tzchori et al 2004), the American eel and the Japanese eel (Katoh & Kobayashi 2001) are of great commercial interest (Jing & Li 1999;Tsukamoto & Arai 2001;Ringuet et al 2002;Altun et al 2005). Consequently, a decrease in European (Limburg et al 2003;Dannewitz et al 2005), American (Wirth & Bernatchez 2003) and Japanese eel (Tseng et al 2003) catches during the past decades in Europe, America and Asia, respectively, has inspired many studies on physiological (Ellerby et al 2001a, b), ecological (Poole & Reynolds 1998;Tzeng et al 1999;Okamura et al 2002;Bardonnet & Riera 2005;Palstra et al 2006) and genetic (Jing & Li 1999;Wirth & Bernatchez 2001Mank & Avise 2003;Tseng et al 2003;Dannewitz et al 2005) aspects of eel biology and an increased concern over the eel restocking strategy (Ringuet et al 2002).…”