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Semilunar Ovarian Activity of the Gulf Killifish, Fundulus grandis, under Controlled Laboratory Conditions
Shyh-Min Hsiao and Albert H. Meier
Vol. 1988, No. 1 (Feb. 5, 1988), pp. 188-195
Stable URL: http://www.jstor.org/stable/1445937
Page Count: 8
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Ovarian activities were examined throughout semilunar spawning cycles of Fundulus grandis maintained indoors on constant photoperiodic (LD 12:12) and temperature (23 C) conditions. Daily egg collections indicated a 13.6 d spawning cycle that was correlated with cyclic variations of gonadosomatic indexes (GSI: gonad weight/body weight × 100). An increase in GSI anticipating the spawning peak apparently resulted from an increase in formation of hydrated oocytes and ovulated eggs. Follicles containing peripheral germinal-vesicle (PGV) oocytes, oil-droplet (OD) dispersed oocytes and mature oocytes, were collected throughout the cycle and observed in vitro. PGV oocytes were more likely to undergo germinal vesicle breakdown in culture with the approach of peak spawning activity. Almost all OD dispersed oocytes became mature oocytes which did not ovulate in vitro although most mature oocytes collected did. Ovulation apparently requires an additional in vivo stimulus. Thus, oocyte maturation and ovulation appear to be the determining factors leading to increased spawning during the semilunar cycle.