Evidence of daily spawning in natural populations of the New Zealand snapper Pagrus auratus (Sparidae)

New Zealand snapper, Pagrus auratus , were captured by trawling from NE New Zealand over two successive spawning seasons, and examined for acute temporal changes in gonad condition. Fish with oocytes completing final oocyte maturation predominated during the morning, with a peak in ovulated fish occ...

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Bibliographic Details
Published in:Environmental biology of fishes 1993-02, Vol.36 (2), p.149-156
Main Authors: Scott, S.G. (Auckland Univ. (New Zealand). Leigh Marine Lab.), Zeldis, J.R, Pankhurst, N.W
Format: Article
Language:English
Subjects:
Agnatha. Pisces
Animal and plant ecology
Animal, plant and microbial ecology
Animals
Autoecology
Biological and medical sciences
BIOLOGICAL RHYTHMS
Fundamental and applied biological sciences. Psychology
Marine
NEW ZEALAND
NOUVELLE ZELANDE
NUEVA ZELANDIA
OVIPOSICION
OVIPOSITION
OVULACION
OVULATION
PAGRUS
Pagrus auratus
PONTE
RITMOS BIOLOGICOS
RYTHME BIOLOGIQUE
Vertebrata
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Summary:New Zealand snapper, Pagrus auratus , were captured by trawling from NE New Zealand over two successive spawning seasons, and examined for acute temporal changes in gonad condition. Fish with oocytes completing final oocyte maturation predominated during the morning, with a peak in ovulated fish occurring just after midday. Afternoon catches were dominated by fish in which the most advanced oocytes had yet to begin final maturation. This suggests that ovulation is synchronised to occur soon after midday, and the high proportion (up to 100% of the catch) of fish with particular gonad stages captured at any one time indicates that daily spawning involves most of the population. Diurnal changes in oocyte diameter support a daily spawning rhythm, with numbers of large hydrated oocytes peaking in the late morning, followed by the disappearance of these oocyte stages in the afternoon. Snapper captured alive by longlining were returned to the laboratory to examine the relationship between ovulation and probable time of spawning. Unovulated fish generally ovulated close to midday on the day of capture (morning captures), or the following day (afternoon captures). The viability of ovulated eggs (proportion undergoing division after fertilization) decreased markedly after oviduct residence times of over 8 hours. This suggests that natural spawning occurs before the late evening. The results of this study are consistent with anecdotal evidence suggesting that spawning occurs every day during the late afternoon or early evening, and is similar to the reproductive patterns displayed by a number of closely related sparids.
ISSN:0378-1909
1573-5133
DOI:10.1007/BF00002794