Reproductive Endocrinology in chondrichthyans: the present and the future

AWRUCH C. A.

Brisbane

Congreso; Oceania Chondrichthyan Society Conference; 2013

Oceania Chondrichthyan Society

The evolutionary success of Chondrichthyans is greatly attributed to their wide range of reproductive strategies controlled by different endocrine mechanics. Hormonal control of reproduction is mediated by the neuropeptide gonadotropin-releasing hormone (GnRH) that regulates the brain control of gonadal activity via a hypothalamus?pituitary?gonadal (HPG) axis. Chondrichthyans lack of a direct vascular supply from the hypothalamus to the zone of the pituitary where the gonadotropic activity resides, thus transport between these two zones occurs via the general circulation. In the brain of elasmobranchs, two groups of GnRH, GnRH-I and GnRH-II were identified, and the presence of two immunoreactive gonadotropins similar to the luteinising (LH) and follicle stimulating (FSH) hormones was identified in the pituitary. In holocephalans, only GnRH-II has been confirmed, and while gonadotropin activity has been found in the buccal pituitary lobe, the presence of gonadotropin receptors in the gonads remains unknowns. The diversity of reproductive strategies display by chondrichthyans makes it difficult to generalise the control of gametogenesis and steroidogenesis. In both sexes, androgens and estrogens are the main steroids during gonadal growth; while progestins have maturational activity.  Androgens also form the precursors for estrogen steroid production. Estrogens stimulate the hepatic synthesis of yolk and the development of the reproductive tract in females. The role of other gonadal steroids may play remains largely unknown. Future work should concentrate in filling the gaps into the currently knowledge of the HPG axis regulation, and the use of reproductive endocrinology as a non-lethal technique for management of chondrichthyan populations.