Stress inhibition of reproductive endocrine processes in a natural population of the spiny damselfish Acanthochromis polyacanthus

Stress-reproduction interactions were assessed by in situ sampling and laboratory manipulation of fish from a natural population of A. polyacanthus. Mean plasma cortisol concentrations for fish sampled under water immediately after capture were <11 ng mL -1 (range <1 to 42 ng m L-1); the variation was not a function of disturbance before capture, with no differences in mean cortisol concentrations between 5 min time blocks for chase times of up to 30 min. Fish confined for 2 or 6 h after capture showed significant increases in plasma cortisol concentrations, and depression of plasma T and E 2 in females and T and 11KT in males in summer but not in winter. There was no correlation between plasma concentrations of cortisol and sex steroids at capture. Underwater treatment of fish with cortisol had no effect on brood-guarding behaviour. Injection of fish either at capture or 24 h afterwards with human chorionic gonadotropin or luteinizing hormone-releasing hormone analogue had no effect on plasma concentrations of gonadal steroids, which remained low. Incubation in vitro of ovarian follicles from these fish showed that gonadal tissue was still steroidogenically active. This study suggests that inhibition of reproduction by stress in spiny damelfish is above the level of steroid biosynthesis.