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7439719 
Journal Article 
Sex Hormones and Their Role in Gonad Development and Reproductive Cycle of Fishes 
Mukne, A; Momin, M; Betkar, P; Rane, T; Valecha, S; Kumar, P; Behera, P; Christina, L; Kailasam, M; , 
2021 
Springer Singapore 
Singapore 
Recent updates in molecular Endocrinology and Reproductive Physiology of Fish 
1-22 
The development of captive broodstock and reproductive maturation is essential for induced breeding. The reproductive cycle of fish is divided into two phases, that is, growth and maturation phase, which is controlled by the cascade of hormones along the brain-pituitary-gonad (BPG) axis. In this axis, gonadotropin-releasing hormone (GnRH) and dopamine secreted from the brain regulate the gonadotropin secretion from the pituitary. The gonadotropins from the pituitary gland are released into the blood which act on the gonad to trigger the production of the sex steroid hormones. Estradiol-17β (E2) under the control of gonadotropin (follicle-stimulating hormone, FSH) regulates the vitellogenesis and oocyte growth. Maturation-inducing steroid (MIS) or maturation-inducing hormone (MIH) under the control of gonadotropin (luteinizing hormone, LH) regulates the maturation and spawning. In synchronous fish, the level of FSH increases during the vitellogenic phase and drops during follicular maturation and spawning, whereas the LH level is low at vitellogenesis and high before ovulation. The first peak of testosterone occurred during vitellogenesis, and the second peak is observed just prior to spawning. The E2 level remains high during late-vitellogenic and vitellogenic stages and low during post-vitellogenic and hydrated stages. In male, FSH increases gradually at the initial stage of spermatogenesis, reaches peak during testicular growth, and then declined after spawning, whereas LH is low at early spermatogenesis, increases during spermiation, and attained peak during the spawning. In male, the first peak of testosterone is noticed during pre-spawning and the second just prior to the spawning. In asynchronous fish, two peaks of gonadotropins (FSH and LH) are observed in the plasma of multiple spawner female fish (tilapia) during two consecutive spawning. The first peak is evident 2 to 3 days after spawning (vitellogenic phase), and the second peak is noticed just before the next spawning. The knowledge on hormonal cycle will help in the captive breeding of fishes.