The relationship between plasma and ovarian levels of gonadal steroids in the repeat spawning marine fishesPagrus auratus (Sparidae) andChromis dispilus (Pomacentridae) |
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| Authors: | A C Hobby N W Pankhurst |
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| Institution: | (1) Leigh Marine Laboratory, University of Auckland, Private Bag, 92019 Auckland, New Zealand;(2) Department of Aquaculture, University of Tasmania, P.O. Box 1214, Launceston, Tasmania, 7250, Australia |
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| Abstract: | The relationship between plasma and ovarian levels of gonadal steroids was examined in two New Zealand fish species with multiple
spawning cycles of differing length. Snapper (Pagrus auratus) have a daily cycle of oocyte development, ovulation and spawning, whereas demoiselles (Chromis dispilus) spawn over 2–3 days during a repeat spawning cycle of 7–9 days. Ovarian and plasma levels of the gonadal steroids 17β-estradiol
(E2), testosterone (T), 17-hydroxyprogesterone (17P) and 17,20β-dihydroxy-4-pregnen-3-one (17,20βP) were measured in reproductively
active fish captured from the wild. Ovarian levels of E2, T and 17P changed in relation to spawning cycle and gonad stage in both snapper and demoiselles. E2 and T levels were detectable at all times, but highest during vitellogenesis in both species. Cyclic changes of 17P occurred
in both species, and levels appeared to depend on the rate of conversion of 17P to other hormones. No changes in ovarian levels
of 17,20βP were detected in relation to stage of the spawning cycle in snapper; however, ovarian levels of 17,20βP were highest
in demoiselles before spawning when fish undergoing final oocyte maturation predominated. Plasma levels of E2 and T were strongly correlated with ovarian concentrations (r=0.850 and r=0.819 for E2 and T respectively) in demoiselles but there was poor correlation between ovarian and plasma levels of 17P and 17,20βP (r=0.004
and 0.273 respectively), or between ovarian and plasma levels of E2, T, 17P or 17,20βP of snapper (r=0.135, 0.277, 0.131 and 0.279). The poor correlation between plasma and ovarian levels of
some steroid hormones suggests that plasma concentrations of steroids may not adequately reflect the reproductive status of
the fish during short-term cyclic ovarian changes. It is suggested that this disparity is likely to be most marked in species
with ovulatory periodicity of short duration. |
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