Ovarian germinal epithelium, oocyte development and the secretory epithelium in monkfish (Lophius americanus Valenciennes).

Histological examination of ovarian morphology was conducted on the monkfish, Lophius americanus. The ovary is of the cystovarian type, that is, with a lumen. However, ovarian morphology is quite unique, compared to other fishes, in that ovarian lamellae only originate along the ventral ovarian wall rather than around the periphery. They may branch at their base, but are otherwise unbranching. Furthermore, the germinal epithelium that is, the site of germ cell production, is described for the first time in L. americanus. The germinal epithelium is uniquely restricted around the base of each lamellae rather than being distributed along lamellar epithelia. Folliculogenesis, the process whereby ovarian follicles are formed, is completed in the Perinucleolar Step of the Primary Growth Stage. As oocytes grow and mature, they are increasingly observed towards the apex of the unbranched lamellae where ovulation occurs. The appearance of small vesicles within yolk at the vegetal pole was observed in oocytes during maturation. Prior to ovulation, cells of the ovarian epithelium produce a mucogelatinous matrix that forms the veil in which eggs, after fertilization, become suspended in the water column until hatching.