Reproductive performance of common dentex, Dentex dentex, broodstock held under different photoperiod and constant temperature conditions |
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Authors: | M Pavlidis S Keravec L Greenwood B Mourot AP Scott |
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Institution: | (1) Institute of Marine Biology of Crete, P.O. Box 2214, GR-71003 Heraklio, Crete, Greece;(2) Department of Biology, University of Crete, P.O. Box 2208, GR-71409 Heraklio, Crete, Greece;(3) Centre for Environment, Fisheries, and Aquaculture Science, Fish Diseases, The Nothe Barrack Road, Weymouth Dorset, DT4 8UB, UK;(4) INRA - SCRIBE, Campus de Beaulieu, 35042 Rennes Cedex, France |
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Abstract: | The effect of photoperiod and temperature on the timing and the quality of spawning, and on associated endocrine changes in
circulating 17β-oestradiol, 11-ketotestoserone (11-KT) and vitellogenin (Vtg) were investigated in common dentex, Dentex dentex, undergoing their second reproductive cycle. The possibility was also explored of using the measurement of steroids in the
culture water of broodstock tanks, rather than in individual blood plasma samples, as a potentially useful tool for assessing
the physiological state of a fish without disturbing them. One group of fish was exposed to a simulated natural seasonal cycle
and ambient temperature (CONTROL). The other two groups were exposed to simulated seasonal photoperiod cycles (12 month-long)
but which were phase-shifted either three months before (ADVANCED) or after (DELAYED) the natural cycle. Temperature was kept
at 19.4±0.9 °C all-year-round. In the CONTROL, spawning started in mid-April and lasted until mid-June, while in the ADVANCED
group, spawning started 4 months earlier and in the DELAYED group 2 months later than the CONTROL. The total egg production,
egg quality, hatching rate, relative fecundity, and spawning index of the experimental groups were similar to the controls.
The differences in spawning time induced by photothermal manipulation were associated with a difference in the timing of peak
concentrations of plasma E2, 11-KT and Vtg. In all three groups, the amounts of conjugated 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) and free and sulfated
11-KT which could be extracted from the water during the spawning period were significantly higher than those found in the
preovulatory period. However, the differences were mostly less than 2-fold suggesting that, at least under the conditions
employed in this study, the method was of limited use for non-intrusive detection of gonadogenesis and spawning (as had been
hoped). The observed differences in spawning time and in the seasonal changes of sex steroids and Vtg confirm and extend the
findings on marine fish.
This revised version was published online in August 2006 with corrections to the Cover Date. |
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Keywords: | common dentex Dentex dentex photoperiod sex steroids spawning period vitellogenin |
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