Publication Abstract

Gonadotrophin-releasing hormone agonist enhances milt fluidity and plasma concentrations of progestogens in male Atlantic halibut (Hippoglossus hippoglossus)

Gonadotrophin-releasing hormoneagonist enhances milt fluidity and plasma concentrations of progestogens in male Atlantichalibut (Hippoglossus hippoglossus)

E.L.M. Vermeirsson, R. Shields, C. Mazorra de Quero and A.P. Scott In two separate spawning seasons, sperrniatingmale Atlantic halibut were implanted with pellets containing gonadotrophin-releasinghormone agonist (GnRHa). Males were bled repeatedly, and milt samples were collected.Blood samples were assayed for free and conjugated steroids: testosterone.11-ketotestosterone. 17,20α-dihydroxy-4-pregnen-3-one (17,20α-P). 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P), 17,20β,21-trihydroxy-4- pregnen-3one and steroids with a 17,20β configuration. Towards the endof the first season, pellets were implanted into three wild-caught and threehatchery-reared males. No control fish were available. The major progestogen in plasma wasidentified as sulphated 5β -pregnane-3β,17,20β-triol(3β, 17,20β-P-5β-S). Concentrations of this steroid werestimulated by the GnRHa. Sulphated 17,20β-P was also identified in the plasma. but at 10-fold lowerconcentrations than 3β,17,20β-P-5β-S. In the middle of the secondseason, pellets were implanted into five hatchery-reared males: five unimplanted maleswere used as controls. Levels of androgens fell following GnRHa treatment, levels ofprogestogens rose briefly. and there was a significant increase in the fluidity of themilt. Of all the measured steroids, free and sulphated 17,20α-P showed the best correlation with miltfluidity.

Reference:

E.L.M. Vermeirsson, R. Shields, C. Mazorra de Quero and A.P. Scott, 2000.Gonadotrophin-releasing hormone agonist enhances milt fluidity and plasma concentrationsof progestogens in male Atlantic halibut (Hippoglossus hippoglossus). Fish Physiology andBiochemistry, 22(7): 77-87.

E.L.M. Vermeirsson*, R. Shields, C. Mazorra de Quero and A.P. Scott*

Fish Physiology and Biochemistry, 22(7): 77-87