Zoological Studies

Vol. 51 No. 7, 2012

The Reproductive Biology of Pempheris schwenkii (Pempheridae) on Okinawa Island, Southwestern Japan

Keita Koeda1,*, Taiki Ishihara1, and Katsunori Tachihara2

1Graduate School of Engineering and Science, University of the Ryukyus, 1 Senbaru, Nishihara, Okinawa 903-0213, Japan
2Faculty of Science, University of the Ryukyus, 1 Senbaru, Nishihara, Okinawa 903-0213, Japan.   E-mail:ktachiha@sci.u-ryukyu.ac.jp

Keita Koeda, Taiki Ishihara, and Katsunori Tachihara (2012) The reproductive biology of Pempheris schwenkii, one of the most common nocturnal fishes in Okinawan waters, was studied using a total of 1834 specimens (3.1-125.9 mm standard length, SL) collected around Okinawa I.  The spawning season was estimated to occur from Jan. to June, with a peak from Feb. to May, based on monthly changes in the gonadosomatic index and histological observations of the ovaries.  The relationship between the SL and the appearance of mature females, and the monthly growth of the 0+ group suggested that maturity occurred at ca. 70 mm SL, corresponding to 1 yr after hatching.  Spawning was not related to the lunar cycle.  The batch fecundity of P. schwenkii was calculated as ca. 700-4100 eggs.  Pempheris schwenkii appeared to spawn at night based on diurnal changes in the frequency of females exhibiting hydrated ovaries and postovulatory follicles.  Such nighttime spawning seems to reduce the risk of predation of adults and eggs, which may be an adaptive characteristic of nocturnal fishes.

Key words: Nocturnal, Pempheris schwenkii, Reproduction, Spawning season, Spawning time.

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