Adequate interval of sGTH administration to induce vitellogenesis, and induction of ovulation by simultaneous administration of sGTH and 17 alpha-hydroxyprogesterone in the Japanese eel

In this study, the effects of weekly and biweekly administrations of salmon gonadotropin fraction (sGTH), via an emulsion prepared with lipophilized g elatin (LG emulsion), on the induction of vitellogenesis in the Japanese ee l were compared to determine the adequate intervals of hormone administrati on. The effectiveness of simultaneous administration of sGTH and 17 alpha-h ydroxyprogesterone (17 alpha P) using LG emulsion for the induction of fina l maturation and ovulation was also examined. Immature female Japanese eel (cultured eel and silver eel) were administered sGTH with LG emulsion weekl y (2 mg/kg BW) or biweekly (4 mg/kg BW). In the fish injected biweekly with LG emulsion containing sGTH, biweekly cyclic fluctuations in the body weig ht (BW) and plasma levels of testosterone, estradiol-17 beta and sGTH II we re repeated in response to the injection of sGTH. It took a longer period f or the biweekly injected fish to complete vitellogenesis compared with the fish injected weekly. The weekly injections of sGTH were more effective tha n the biweekly injections in inducing vitellogenesis in the Japanese eel. T he LG emulsion containing sGTH in the aqueous phase and 17 alpha P in the o il phase was prepared. Hormone releasing properties were investigated by mo nitoring plasma profiles of hormones in immature eel. Significant differenc es in the plasma profiles of sGTH II and 17 alpha P were not observed betwe en simultaneous administration of sGTH and 17 alpha P and single administra tion of sGTH or 17 alpha P. Following induction of vitellogenesis, females that exhibited a rapid increase of BW and had oocytes at migratory nucleus stage were injected with sGTH and 17 alpha P at the same time using LG emul sion. As a result, all females injected with sGTH and 17 alpha P ovulated. Simultaneous administration of sGTH and 17 alpha P can be useful for the in duction of final maturation and ovulation in the Japanese eel.