Final maturation and ovulation of oocytes of the goldeye, <i>Hiodon alosoides</i> (Rafinesque), <i>in vitro</i>

Abstract

Oocytes from preovulatory goldeye were cultured in vitro and final maturation was observed in response to treatment with piscine gonadotropins (GtH) and progestational steroids. Final maturation consisted of nuclear migration and breakdown, and coalescence of yolk material to form a single large oil droplet. Both events were under hormonal control with median effective dose values of 1–5 μg∙mL −1 for piscine GtH and 0.1–0.6 μg∙mL −1 for pregnenolone, progesterone, 17αOH pregnenolone, 17αOH progesterone, and 17α,20β-dihydroxy-4-pregnen-3-one. Neither cortisol nor triiodothyronine potentiated the effects of GtH or progestogens, and both were ineffective alone as was human chorionic gonadotropin. Ovulation was observed in some treatments with GtH, and prostaglandin F 2α salt stimulated ovulation of oocytes matured with GtH or 17α,20β-dihydroxyprogesterone. A synthetic analogue of luteinizing hormone-releasing hormone, LH-RHA, had no effect on maturation or ovulation, in contrast to its inhibitory action on GtH-stimulated steroid production in mammals. Follicles from fish in mid and late stages of vitellogenesis were unresponsive to hormone treatment in vitro.