Effects of Water Temperature and Estradiol-17β on the Sex Ratio and Growth of the Japanese Eel, Anguilla japonica

This study investigated the effects that water temperature and the administration of estradiol-17s (E2) had on the sex ratio and growth of the Japanese eel, Anguilla japonica. Glass eels (total length≒6.5 cm) were differentiated into an E2 group and an E2-free group and then they were reared for about four months at three water temperature levels of 20C, 24C, and 28C. The results showed that the young eels survived normally at the rearing water temperature of ≥24 o C, and grew to a mean size of 20 cm (total length). In the E2-free group, temperature was not found to increase the sex ratio (feminizing rates); however, the sex ratio of the E2-administrated group was found to be a little higher at a high temperature (28C). The growth of the E2 group was lower than the growth of the E2-free group at 24 o C and the E2 concentration levels in the plasma at 24 o C were found to be significant after the end of the E2 administration period (178 days). Therefore, we thought that long-term administration of E2 must be considered to be the reason for growth decline in spite of the prominent sex ratio effect. Our results indicate that temperature was not related to an increase in the feminizing rate (sex ratio) in the Japanese eel, Anguilla japonica, and other environmental factors (rearing density, salinity, etc.) that have the possibility of inducing ovarian differentiation must be investigated.