In Vitro Oocyte Maturation and Ovulation in Rainbow Trout (Salmo gairdneri), Northern Pike (Esox lucius), and Goldfish (Carassius auratus)

Abstract

The endocrine processes which control oocyte maturation (resumption of meiosis) and ovulation have been studied in vitro in the trout Salmo gairdneri. Follicular maturation is ultimately under the control of a pituitary gonadotropin which induces the follicle to synthesize specific steroids; these steroids act in turn directly on the oocyte to promote maturation. The systematic study of the in vitro efficiency of various steroids have shown that 17α-hydroxy-20β-dihydroprogesterone plays a preferential role in initiating maturation; this steroid has a high affinity for a plasma protein system. The efficiency of this steroid, similarly to the efficiency of the gonadotropin, can be modulated by other circulating steroids. The precise chronology of some events of follicle maturation have been defined using inhibitors of protein and RNA synthesis.The ovulatory process (sensu stricto: expulsion of matured oocyte from the follicular envelopes) has been experimentally dissociated from oocyte maturation, and some mediators likely to act on ovulation have been identified.These data permit the consideration of novel means of intervention at the ovarian level to synchronize maturation and ovulation in fish, in order to give new tools for progress in aquaculture.