Use of an Emulsion Prepared with Lipophilized Gelatin for the Induction of Ovarian Maturation in the Japanese Eel Anguilla japonica

Abstract

A new type of water-in-oil-in-water (W/O/W) emulsion using lipophilized gelatin (LG) and cotton-seed oil was developed for the administration of salmon gonadotropin (sGtH) to induce ovarian maturation in the Japanese eel. Hormone-releasing properties of the LG emulsion were compared with a W/O type emulsion prepared with Freund's incomplete adjuvant (FIA) and saline solution in in vitro and in vivo experiments. These results indicated that the LG emulsion had hormone-releasing properties different from those of the saline solution and the FIA emulsion. Cultured immature female Japanese eel (BW, 566 to 1017 g) received a weekly intramuscular injection (total of 10 injections) of the LG emulsion, the FIA emulsion or the saline solution, each of which contained sGtH. In the group treated with LG emulsion containing sGtH, all fish matured showing small individual variations in GSI and percent increases in body weight. Although the FIA emulsion was also effective in inducing ovarian maturation, it is possible that ovarian maturation was inhibited by antibodies produced against sGtH. Administration of sGtH in saline solution required a longer period of time for the completion of ovarian maturation. Therefore, it appeared that the LG emulsion containing sGtH was more effective than other preparations in inducing ovarian maturation in eel.