In the current protocol for obtaining eel eggs, females are injected
one time each week with SPE to promote oocyte growth. Mature females
that have full-grown oocytes need to be successively injected
with SPE for priming and maturation-inducing steroid (MIS) or its precursor
to induce ovulation following final oocyte maturation including
resumption of meiosis and germinal vesicle breakdown (Kagawa et al.,
2005).Without these treatments, the oocytes rarely undergo final oocyte
maturation and ovulation and mostly become degenerated in response
to further weekly injections of SPE (Kagawa et al., 2005). Administration
of MIS is indispensable for consistently acquiring eel eggs. Moreover,MIS
administration has an advantage that ovulated eggs can be obtained at a
planned time because ovulation occurs about half a day after theMIS injection
into fully mature females.