ABSTRACT
The gonads of vertebrates produce gametes and sex hormones. In salmonids, the major sex hormones are estradiol (E2), testosterone (T) and 17α,20β-dihydroxy-4-pregnene3-one (17,20P) in the female and T, 11-ketotestosterone (11KT) and 17,20P in the male. The gonads are stimulated by gonadotropic hormones (GTHs) from the pituitary. As in other gnathostomes, the teleost fi shes have two pituitary GTHs; follicle-stimulatinghormone (FSH) and luteinizing hormone (LH). The pituitary in its turn is controlled from the brain, especially the hypothalamus, and in the salmonids the main control of GTHs is stimulatory and exerted by gonadotropin-releasing hormone (GnRH). This system controlling reproduction constitutes the brain-pituitary-gonad (BPG) axis (Fig. 5.1). Feedback mechanisms are acting on this axis, i.e., gonadal hormones affect the axis on the brain and/or pituitary level. In this review, we aim at covering what is known about the BPG-axis in the Atlantic salmon.
