pointed out that spawning on outgoing tides is a 

 common phenomenon among coastal marine 

 fishes in the tropics, and he believed it evolved as a 

 strategy for ensuring that eggs and larvae are 

 transported away from the heavy concentration of 

 predators in shallow water. Johannes noted that 

 nocturnal spawning is also common in tropical 

 reef fishes and serves to reduce predation both on 

 the eggs and on the spawners. 



The first P. sexfilis spawning of the year appears 

 to be anomalous in that it occurs relatively late 

 with respect to the last quarter. If offshore trans- 

 port confers an important selective advantage on 

 P. sexfilis, the lateness of the first spawning is 

 maladaptive because it results in release of eggs 

 early relative to the outgoing tide (see Figure 3). 

 The initial phase of the spawning season may thus 

 result in few viable offspring and could represent a 

 gradual initiation of the main spawning season, 

 delayed perhaps by the lower water temperatures 

 which usually prevail during the first spawning 

 month (Batheni"). 



No observations on the spawning behavior of a 

 polynemid fish have been published previously. In 

 P. sexfilis the sexes apparently pair and spawn 

 after a brief courtship involving rapid following 

 and nosing of one fish by another. The spawning 

 behavior of this species is similar in many respects 

 to that of the Pacific bonito, Sarda chiliensis, in- 

 cluding behaviors described by Magnuson and 

 Prescott (1966) as "circle swimming," "tail nos- 

 ing," and "following." The circling behavior noted 

 among P. sexfilis may have been imposed by the 

 confinement of the net enclosure, but S. chiliensis 

 also showed tight circling behavior at the time of 

 gamete release in a very large tank at Marineland 

 of the Pacific, and circling prior to spawning occurs 

 naturally in mullets ( Helfrich and Allen 1 975) and 

 some (perhaps many) other tropical fishes (R. E. 

 Johannes, Hawaii Institute of Marine Biology, 

 P.O. Box 1346, Kaneohe, HI 96844. Pers. com- 

 mun., December 1977). The circling behavior dur- 

 ing spawning observed in captive P. sexfilis thus 

 may not be abnormal for this species but may, as 

 Magnuson and Prescott (1966) theorized for S. 

 chiliensis, serve to enhance the probability of fer- 

 tilization. 



'-^ Acknowledgments 



We wish to thank R. E. Johannes for reading 

 and commenting on the manuscript, and Lloyd 

 Watarai, Steven Shimoda, Michael Muranaka, 

 and Michael Matsukawa for their help in main- 

 taining fish and collecting data. This work was 

 supported by the University of Hawaii Sea Grant 

 College Program, NOAA, Office of Sea Grant, U.S. 

 Department of Commerce, under Grant No. 04-3- 

 158-29, 04-5-158-17, 04-6-158-44026, and 04-6- 

 158-441 14, and by the State of Hawaii through the 

 Hawaii Insitute of Marine Biology, the Office of 

 the Marine Affairs Coordinator, and the Depart- 

 ment of Planning and Economic Development. 



Literature Cited 



Helfrich, P., and P. M. Allen. 



1975. Observations on the spawning of mullet, Creni.*7iu^j/ 

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 cronesica 11:219-225. 



HOSAKA, E. Y. 



1944. Sport fishing in Hawaii. Bond's, Honolulu, 198 p. 



Johannes, R. E. 



1978. Reproductive strategies of coastal marine fishes in 

 the tropics. Environ. Biol. Fishes 3:65-84. 



Leis, J. M., AND J. M. Miller. 



1976. Offshore distributional patterns of Hawaiian fish 

 larvae. Mar. Biol. (Berl.) 36:359-367. 



Lowell, N. E. 



1971. Some aspects of the life history and spawning of the 



moi {Polydactylus sexfilis). M.S. Thesis, Univ. Hawaii, 



45 p. 

 MAGNU.SON, J. J., AND J. H. PRESCOTT. 



1966. Courtship, locomotion, feeding and miscellaneous 



behaviour of Pacific bonito iSarda chiliensis). Anim. 



Behav. 14:54-67. 

 May, R. C. 



1976. Studies on the culture of the threadfin, Polydactylus 



sexfilis, in Hawaii, FAO Technical Conference on 



Aquaculture, Kyoto, Jpn., 26 May-2 June 1976. FIR:AQ/ 



Conf/76/E.5. FAO, Rome, 5 p. 



ROBERT C. May 



Hawaii Institute of Marine Biology 

 Kaneohe, Hawaii 



Present address: Asian Development Bank 

 P.O. Box 789, Manila, Philippines 



Gerald S. Akiyam.a 

 Michael T. Santerre 



Hawaii Institute of Marine Biology 

 P.O. Box 1346, Kaneohe, HI 96744 



'"Bathen, K. 1968. A descriptive study of the physical 

 oceanography of Kaneohe Bay, Oahu, Hawaii. Univ. Hawaii, 

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