The efficacy of exogenous hormones in stimulating changes in plasma steroids and ovulation in wild black bream Acanthopagrus butcheri is improved by treatment at capture

Sexually mature female black bream were captured by rod and line and inject ed with saline, human chorionic gonadotropin (hCG) or luteinizing hormone r eleasing hormone analogue (LHRHa) at capture, or 24 h post capture (saline and LHRHa treatments only). All fish were bled and checked for ovulation fo r 5 days post injection. Plasma levels of oestradiol (E-2), testosterone (T ), 17,20 beta-dihydroxy-4-pregnen-3-one (17,20 beta P) and cortisol were de termined by radioimmunoassay. Saline-injected fish ovulated only on day 1, whereas treatment with LHRHa or hCG resulted in fish ovulating throughout t he experiment. Treatment with LHRHa at capture resulted in a better ovulato ry response than treatment with hCG at capture or LNRHa 24 h post capture. Plasma E-2 levels in saline-injected fish were high at capture and had sign ificantly dropped 1 day after capture. Injection with hCG or LHRHa at captu re resulted in plasma E-2 levels remaining significantly elevated for 2 day s post injection. Injection of LHRHa 24 h post capture failed to significan tly elevate plasma E-2 levels over controls. Plasma T levels were similar t o E-2 profiles. Plasma levels of 17,20 beta P were not significantly differ ent between any treatments, but showed a tendency to increase after capture . Plasma cortisol levels showed no treatment effects and were initially low at capture before becoming elevated between days 1 and 2 post capture. The se results show that capture and handling stress reduce the responsiveness of fish to exogenous hormone treatment and that best results are obtained i f hormonal treatment is administered at the time of capture. (C) 2000 Elsev ier Science B.V. All rights reserved.