Davis and West Reproductive biology of Lutjanus vittus from North West Shelf of Australia 



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° September 



° November 



 February 



• April 



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200 240 

 Length (mm) 



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Figure 1 1 



Relation between batch fecundity and fish length of Lutjanus 

 vittus at four different spawning periods (scales are logged). 



ing has been reported in many teleosts and some 

 lutjanids, with most spawning activity close to the time 

 of the full moon; e.g., L. vaigiensis (Randall & Brock 

 1960), L. griseus (Starck 1970), L. synagris (Reshet- 

 nikov & Claro 1976), L. kasmira, L. rufolineatus, and 

 P. multidens (Mizenko 1984; although aquarium popu- 

 lations of L. kasmira spawned at the new and full 

 moon [Suzuki & Hioki 1979]). 



Many hypotheses have been proposed to explain why 

 lunar reproductive cycles have developed in fishes (see 

 reviews by Johannes 1978, Thresher 1984, Gladstone 

 & Westoby 1988, Robertson et al. 1990). We cannot 

 adequately explain why L. vittus has a well-developed 

 lunar reproductive pattern. Spawning is probably 

 linked to the lunar tidal cycle rather than moonlight 

 per se, as it occurred chiefly after new and full moons 

 and during daylight. The North West Shelf is a region 

 of strong semidiurnal tides which flow predominantly 

 cross-shelf at the shelf break and alongshelf near the 

 coast (Holloway 1983). Spawning during spring tides 

 would therefore disperse the eggs of L. vittus alongshelf 

 rather than cross-shelf. There would be a clear advan- 

 tage for larvae if they were advected to the midshelf or 

 further offshore because these areas have greater pro- 

 ductivity (Young et al. 1986). There is, however, no 

 evidence for dispersal offshore; both larvae and adults 

 of Lutjanus spp. are primarily found on the inner shelf 

 (Leis 1987). 



Frequency of spawning was determined from the 

 proportion of females with postovulatory follicles. Our 

 findings indicate that postovulatory follicles persist for 



<ld, whereas studies on other species have found that 

 they persist for <15h (Takita et al. 1983), <2d (Hunter 

 & Goldberg 1980, Hunter et al. 1986, Clarke 1987), or 

 slightly longer (Alheit et al. 1984). Our data on 

 postovulatory follicles suggest that females on average 

 spawn about 22 times each lunar month. The propor- 

 tion of females spawning each day peaks about 3d 

 after the new moon and 6 d after the full moon. 



It seems unusual that L. vittus spawns during early 

 afternoon. Thresher (1984) reviewed 22 pelagic egg- 

 producing families, including lutjanids, and found that 

 most spawned around dusk, as did Colin & Clavijo 

 (1988) who examined 26 species associated with coral 

 reefs. Lutjanids produce pelagic eggs (Suzuki & Hioki 

 1979) and all other reports indicate that they spawn 

 at or after dusk (Wicklund 1969, Starck 1970, Suzuki 

 & Hioki 1979). Possibly spawning is linked to the state 

 of the tide, rather than the time of day per se. In both 

 1982 and 1988, spawning activity coincided with ris- 

 ing tides; it may have been coincidental that these 

 were during daylight hours. 



Batch fecundity increased exponentially with fish 

 length and linearly with fish weight. The variability in 

 batch fecundities did not appear to be due to errors in 

 using the gravimetric method. The mean coefficient of 

 variation of estimates was 0.11, and it never exceeded 

 0.21. Care was taken to exclude ovaries that had par- 

 tially spawned (identified by the presence of early-stage 

 postovulatory follicles), and only those ovaries that had 

 a clearly identified mode of partly-hydrated oocytes 

 were used for estimates. Also, batch fecundities did 

 not appear to differ between sampling periods. One 

 might have expected a decline in fecundity as ovary 

 weight declined over the season. Another possible rea- 

 son for the variability in batch fecundity might have 

 been that samples were taken at different phases of 

 the lunar cycle. However, our data are inadequate to 

 test this hypothesis. 



Comparison of the fecundity of L. vittus with that of 

 other lutjanids is not particularly useful, due to incon- 

 sistencies in methods of estimation and uncertainty as 

 to whether true batch fecundities have been estimated 

 (see review by Grimes 1987). It is, however, useful to 

 consider the energetic costs of spawning by L. vittus 

 considering its high annual fecundity. A 300 mm long 

 female L. vittus would shed about 7.6 million eggs 

 annually if it spawned 150 times/yr, or 4.5 million eggs 

 if it spawned 90 times/yr. Assuming a calorific content 

 for dried eggs of 25kJ/g (the mean for a range of ga- 

 doids; Hislop & Bell 1987), then the annual energy 

 expended on spawning (not including reproductive be- 

 havior) would be -1300 kJ for 90 spawnings, and 

 2200 kJ for 150 spawnings. Estimation of reproductive 

 effort or efficiency (egg energy/dietary energy x 100) 



