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1 November 2007 Oviposition Cycle in the Oviparous Fish Xenopoecilus sarasinorum
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To clarify the reproduction of the oviparous teleost Xenopoecilus sarasinorum, changes in oocyte composition and oviposition cycle were investigated. After release, a batch of spawned eggs hung from the urogenital pore by attaching filaments (36.3±0.8 in number, n=31; about 4.3–7.8 mm in length, 5–8 μm in diameter) on the chorion (egg envelope) in the vegetal pole region. Females accommodated a cluster of fertilized eggs in a belly concavity until the embryos hatched. Hatching of embryos took place from 18–19 days after oviposition (25°C). Between 0–2 days following hatching, the attaching filaments disappeared from the urogenital pore. Between 3 and 4 days following hatching, most of the females spawned again. The growth of oocytes proceeded slowly throughout the period when the egg cluster was carried in the belly, and no ovulation occurred during this period. If the current brood was accidentally lost, the day of the next oviposition was sooner. This might imply that carrying embryos in the belly affects endocrine activity, as in viviparous reproduction.

Takashi Iwamatsu, Hirokuni Kobayashi, Yasushi Shibata, Masahiro Sato, Nobuyoshi Tsuji, and Ken-ichi Takakura "Oviposition Cycle in the Oviparous Fish Xenopoecilus sarasinorum," Zoological Science 24(11), 1122-1127, (1 November 2007).
Received: 17 May 2007; Accepted: 1 July 2007; Published: 1 November 2007

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