Stress-induced changes in concentrations of plasma sex steroids in black bream

Cortisol levels of black bream Acanthopagrus butcheri at capture did not ch ange with time of day, gonadal stage or season and were 1.9 +/- 0.2 and 2.8 +/- 0.4 ng ml(-1) for male and female fish, respectively. Confinement resu lted in significantly elevated cortisol levels at all time periods; however , levels after 24 h of confinement a ere significantly lower than peak cort isol levels (15 min for males and 1 h for females). Confinement stress resu lted in reduced levels of 17 beta-oestradiol (E-2) and testosterone (T) wit hin 1 h in sexually mature females. In mature males, suppression of T and 1 1-ketotestosterone (11KT) occurred after 30 min and 6 h of confinement, res pectively. The relationship between confinement stress and levels of 17,20 beta-dihydroxy-4-pregnen-3-one (17,20 beta P) was more complex, with levels in males being elevated after 15 min and 24 h and suppressed after 6 h of confinement. In contrast, 17,20 beta P levels in females were elevated afte r 1 h of confinement. In regressed females, plasma E-2 and T concentrations were low at capture and were not affected by confinement stress whereas pl asma 17,70 beta P was elevated within 1 h. This study indicates that stress exerts a rapid inhibitory effect on gonadal steroidogenesis. (C) 1999 The Fisheries Society of the British Isles.