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Prostaglandins are involved in the reproductive processes in a variety of animals, including crustaceans. It was found that polychaetes, the best maturation diet for shrimp broodstock, possessed the greatest variation of prostaglandin Esub(2) (PGEsub(2)) when compared with other live feeds. The level of PGEsub(2) varied according to sizes, feed intake, sources and type of polychaete. The matured and also larger sand polychaete Perinereis sp. contained higher PGEsub(2) levels than younger and smaller sand polychaetes (18.16+-5.82 ng PGEsub(2)/mg protein for polychaetes at an average length of 10 cm up to 160.8+-37.09 ng PGEsub(2)/mg protein for polychaetes at an average length of 17 cm). The PGEsub(2) levels in ovaries and haemolymph of female shrimp fluctuated with the developmental stage of the ovaries. The highest concentration of PGEsub(2) in haemolymph was at stage 3 of ovarian development, whereas the highest concentration of PGEsub(2) in shrimp ovaries was at stage 4. In vitro incubation of Penaeus monodon pre-vitellogenic oocytes with polychaete extract and synthetic PGEsub(2) demonstrated that both PGEsub(2)s enhanced oocyte development, especially during late development and ovulation. The putative role of PGEsub(2) from polychaetes or the presence of PGEsub(2) in polychaetes may be a factor in their role as a dietary constituent required for shrimp oocyte development.

Gonadotropin-releasing hormone in Cyprinidae as in other vertebrates functions as a brain signal which stimulates the secretion of luteinizing hormone from the pituitary gland. Two forms of gonadotropin-releasing hormone have been identified in cyprinids, chicken gonadotropin-releasing hormone II and salmon gonadotropin-releasing hormone. Hypophysiotropic functions are fulfilled mainly by salmon gonadotropin-releasing hormone. The only known factor having an inhibitory effect on LH secretion in the family Cyprinidae is dopamine. Most cyprinids reared under controlled conditions exhibit signs of reproductive dysfunction, which is manifested in the failure to undergo final oocyte maturation and ovulation. In captivity a disruption of endogenous gonadotropin-releasing hormone stimulation occurs and sequentially that of luteinizing hormone. In addition to the methods based on the application of exogenous gonadotropins, the usage of a method functioning on the basis of hypothalamic control of final oocyte maturation and ovulation has become popular. The replacement of natural gonadotropin-releasing hormones with chemically synthesized gonadotropin-releasing hormone analogues characterized by amino acid substitutions at positions sensitive to enzymatic degradation has resulted in a centuple increase in the effectiveness of luteinizing hormone secretion induction. Combining gonadotropin-releasing hormone analogues with dopamine inhibitory factors have made it possible to develop an extremely effective agent which is necessary for the successful artificial reproduction of cyprinids.

The question of whether the ovulation and spawning time in chub mackerel Scomber japonicus is entrained by a circadian rhythm was raised by our previous experiments. Further questions were also raised about whether the time course of human chorionic gonadotropin (hCG)-induced final oocyte maturation (FOM) and ovulation reflected the natural time course induced by endogeneous pituitary gonadotropin (GtH). To address these questions, hCG and gonadotropin-releasing hormone analog (GnRHa) were administered at two ‘opposite’ times, 14:00 and 02:00 hours, and the time courses of FOM and ovulation were compared. When hCG was injected, ovulation occurred 33 h post-injection in both groups, regardless of the timing of the hCG injection. The timing of ovulation in chub mackerel depends on the timing of hCG injection, but apparently not on circadian rhythms. When GnRHa was injected, ovulation began at 36 h post-injection of GnRHa, regardless of the timing of injection. These results indicate that the time course of FOM and ovulation in the chub mackerel followed a similar pattern whether stimulated by hCG injection or spontaneous luteinizing hormone (LH) surge because GnRHa induces the secretion of endogenous GtH (primarily LH) from the fish pituitary. Thus, it is concluded that the time course of hCG-induced FOM and ovulation in chub mackerel follows the natural time course induced by endogenous pituitary LH.

Repeated injections of salmon pituitary extract (20 mg per fish per week) induced vitellogenesis in feminized, cultivated Japanese eels (Anguilla japonica). Oocytes were attained at the migratory nucleus stage after 11 or 12 injections. Addition of 17,20β-dihydroxy-4-pregnen-3-one (DHP) into the incubation medium induced germinal vesicle breakdown (GVBD) in the oocytes at the migratory nucleus stage. An injection of DHP (2 µg g^sup -1^ BW), given 24h after an injection of salmon pituitary extract (20 mg fish^sup -1^), succeeded in inducing maturation and ovulation in females which contained occytes at the migratory nucleus stage. Most fish ovulated 15-18h following the DHP injection. Eggs that were ovulated within 15h after the DHP injection showed high fertility and hatchability, but eggs ovulated 18 or 21h after the DHP injection, showed considerably lower fertility and hatchability. A delay between ovulation and stripping of the eggs rapidly decreased both the fertility and hatchability within 6-9h after ovulation, indicating that artificial fertilization must be carried out immediately after ovulation. Repeated injections of human chorionic gonadotropin (hCG) at a concentration of 1 IU g^sup -1^ BW week^sup -1^ induced spermatogenesis, spermiation, and the acquisition of potential for sperm motility in cultivated males. Most males spermiated after the fifth or sixth injection of hCG, and the milt weight gradually increased and remained constant (1-2 g) from the 11th to 31th injection. Sperm motility peaked 24h after each weekly injection, and decreased from the 3^sup rd^ day after the injection. Potassium ions are an essential constituent for the maintenance of motility in the eel spermatozoa. Artificial seminal plasma containing 15.2 mM KCl is applicable as a milt diluent. Using these techniques developed for female and male eels, we have succeeded in obtaining many fertilized eggs from cultivated eels.[PUBLICATION ABSTRACT]

Female Japanese chub mackerel Scomber japonicus of the Tsushima Current subpopulation were collected during the spawning season from March to May 2001. A total of 137 adult females were caught between midnight and daybreak. A considerable number of fish displayed new postovulatory follicles (POF), whereas there was no evidence of germinal vesicle breakdown or hydrated oocytes in any of the fish collected. This suggests a daily spawning synchronicity toward midnight. To estimate the spawning frequency (S), the female reproductive state was classified into four criteria based on the degenerative stage of the POFs and the developmental stage of the oocytes. To stage the POFs according to age and determine the stage duration, ovaries from S. japonicus were induced to spawn in the laboratory and were sampled 0-72 h after ovulation at appropriate intervals. The average S, which is evaluated from four different indices, was 16.9%, corresponding to the average female chub mackerel spawned every 5.9 days (8.5 times) during the 50 days.

The efficiency of medroxyprogesterone acetate (MAP) sponges in combination with either pregnant mare serum gonadotrophin (PMSG) or cloprostenol (PGF2alpha) or both applied intramuscularly for inducing and synchronizing the estrous cycle in non-lactating Kivircik ewes (n=69) was investigated during the natural non-breeding season. Cervical artificial insemination with diluted fresh semen was performed at a fixed time (48 and 60 h) following progestagen withdrawal. There were significant differences between MAP and MAP/PGF2alpha treated ewes and the two other groups, i.e. MAP/PMSG, MAP/PMSG/PGF2alpha in terms of the onset of induced estrous and in terms of estrous response at the first 24+/-6 h, and between MAP and MAP/PGF2alpha groups in terms of the duration of induced estrous. The use of MAP/PMSG was more efficient than the use of MAP or MAP/PGF2alpha in the attainment of early and compact induction and synchronization of estrous in ewes.