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Abstract

This study provides baseline information on the annual reproductive activity of wild
black bream, the effect of capture and confinement on plasma steroid levels, suitable
induced ovulation protocols and the effect of salinity on reproductive development,
induced ovulation and egg fertility and development.
The annual change in reproductive condition and plasma levels of sex steroids in black
bream, was investigated by measuring changes in gonadosomatic index (GSI),
hepatosomatic index (HSI), gonad stage and plasma concentrations of sex steroids. Black
bream have an annual reproductive cycle with a 3 month spawning season in spring / early
summer with daily cycles of gonadal maturation and plasma steroid levels. Elevated levels
of plasma estradio1-1713 (E2), testosterone (T) and 11-ketotestosterone (11KT) were
associated with gonadal recrudescence, and elevated plasma 17,2013-dihydroxy-4-pregnen-
3-one (17,201313) levels were associated with final oocyte maturation and spermiation in
female and male fish respectively.
The stress-induced changes in concentrations of plasma sex steroids in black bream
were investigated by blood sampling at capture and in fish confined for 15, 30 minutes, 1,
3, 6, 12 or 24 hours. Confinement resulted in significantly elevated plasma cortisol levels,
reduced plasma levels of E2 and T within 1 h in females, and suppressed plasma levels of T
and 11KT after 30 min and 6 h respectively in males. Plasma levels of 17,2013P increased
decreased or remained unchanged. This study indicates that stress exerts a rapid inhibitory
effect on gonadal steroidogenesis in black bream.
The effect of hormone therapy to induce ovulation was assessed by injecting mature
female black bream with saline, human chorionic gonadotropin (hCG) or luteinizing
hormone releasing hormone analogue (LHRHa) at capture, or 24 hrs post capture.
Treatment with LHRHa or hCG resulted in fish ovulating throughout the experiment, with
LHRHa treatment at capture resulting in the best ovulatory response. Injection with hCG
or LERHa at capture resulted in the short term elevation of plasma E2 and T, whereas,
injection of LHRHa 24 hrs post-capture did not elevate plasma E2 or T levels over controls.
Plasma levels of cortisol and 17,2013P were unaffected by hormone treatment. These results show that capture and handling stress reduces the responsiveness of fish to
exogenous hormone treatment and that best results are obtained if hormonal treatment is
administered at the time of capture.
The effects of salinity (5, 20 or 35%) on seasonal reproductive development, plasma
steroid levels, the efficacy of LHRHa to stimulate ovulation, sperm motility, and egg
fertility and development to hatching were investigated. Gonadal maturation and seasonal
plasma steroid levels were essentially unaffected by salinity in both sexes. Hormone
therapy resulted in the typical endocrine and ovulatory response in all three salinities,
however, egg production was reduced in fish held at 5 %0. Both fertilisation and sperm
motility were significantly reduced at 5%o. Egg development was best over a salinity range
of 20-35%0.

Item Type:	Thesis - PhD
Authors/Creators:	Haddy, James Andrew
Keywords:	Fishes, Black bream
Copyright Holders:	The Author
Copyright Information:	Copyright 2000 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).
Additional Information:	Thesis (PhD )--University of Tasmania, 2000. Includes bibliographical references
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