Induction of Vitellogenesis

Abstract

In the Japanese eel Anguilla japonica, oocyte development has not been observed to occur under ordinary rearing conditions. Therefore, hormonal treatment is necessary to induce ovarian maturation artificially. Weekly injections of aqueous extract of salmon pituitaries were generally conducted for inducing vitellogenesis (Yamauchi and Yamamoto 1982). 17,20 s s-Dihydroxy-4-pregnen-3-one (DHP) injection is effective for the induction of final oocyte maturation and ovulation after the completion of vitellogenesis (Yamauchi 1990; Ohta et al. 1996). Although the induction of ovarian maturation and fertilization of eggs followed the treatment just mentioned, there are some problems such as variable fertility and hatchability of eggs and low survival rate of larvae. Therefore, it is still necessary to improve the methods of hormonal application in the Japanese eel. We have developed an effective method of salmon gonadotropin (sGTH) application for the induction of vitellogenesis in the Japanese eel, and also investigated the function of sGTH. In this chapter, we summarize our recent studies on the induction of vitellogenesis in the Japanese eel.