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 labo ratory manipulation of fish from a natural population of A. polyacanthus. M ean plasma cortisol concentrations for fish sampled under water immediately after capture were <11 ng mL(-1) (range<1 to 42 ng mL(-1)); the variation was not a function of disturbance before capture, with no differences in me an 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 incr eases 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 a t capture. Underwater treatment of fish with cortisol had no effect on broo d-guarding behaviour. Injection of fish either at capture or 24 h afterward s with human chorionic gonadotropin or luteinizing hormone-releasing hormon e analogue had no effect on plasma concentrations of gonadal steroids, whic h remained low. Incubation in vitro of ovarian follicles from these fish sh owed that gonadal tissue was still steroidogenically active. This study sug gests that inhibition of reproduction by stress in spiny damelfish is above the level of steroid biosynthesis.