ABSTRACT
Much information on the process of oocyte maturation and ovulation has come from in vitro experiments. These experiments have established that GtH acts on the follicular cells to stimulate in situ production of the steroidal mediators of maturation, whereas steroids act directly on the oocytes. This has been shown in several species by removing the follicular layers from the oocytes either enzymically or mechanically. In the rainbow trout, 17a-hydroxy, 20p-dihydroprogesterone and 17oc-hydroxyprogesterone are effective mediators of oocyte maturation, whereas corticosteroids have little or no effect. In other fish such as pike, brook trout and goldfish, not only the progestagens but also 11deoxycorticosteroids are effective. In medaka and catfish also, apart from progestagens, 11-deoxycorticosteroids and 11-oxygenated corticosteroids (e.g. cortisol) are all equally effective (Scott, 1986).
