228 



Fishery Bulletin 9 1(2), 1993 



>. 



o 



c 



cr 



CD 



60 - 



40 



20 





 30 



20 - 



10 - 



-I 

 20 



10 - 



Unyolked 



 hydrated (translucent) 



M late migratory nucleus (becoming translucent) 



M yolk granule (opaque) 



E23 yolk vesicle (translucent) 



□ perinucleolus (transparent) 



■.VAjl 



Yolked 



r 



t 



m 



Yolked 



Ripe 



Ripe 





 10 



5 - 





 10 



5 - 



100 200 300 400 500 600 700 800 900 1000 

 Oocyte diameter (urn) 

 Figure 3 



Oocyte size-frequency distribution and oocyte stage, by 20 um intervals, in Lutjanus 

 vittus ovaries representing the developmental sequence of maturation (see Table 1 for 

 details). An ovary classified as Ripe indicates that it contained late-migratory nucleus- 

 stage oocytes or ripe oocytes. Only oocytes >200um diameter were measured in Ripe 

 stage-5 ovaries, whereas in other ovaries all oocytes >100(im were measured. 



follicles, and proportion of fish 

 with late-migratory nucleus or 

 hydrated-oocyte stages. The 

 former showed a clear cyclical 

 pattern with two peaks of spawn- 

 ing activity during the month of 

 sampling (Fig. 7). Various sinu- 

 soidal curves were fit to the pro- 

 portion of mature fish with 

 postovulatory follicles sampled 

 each day. The following model, 

 which has a period of 29 d and 

 allows one or two peaks of possi- 

 bly unequal heights per period, 

 was chosen: 



y = A+B sin (x) + 



C cos (x) + D sin (2x) + 



E cos (2x), 



(2) 



where t= t hs X 2jt, and t = moon 

 age (d). A regression weighted by 

 the number (n) in each sample 

 was fit to arcsine (angular) root- 

 transformed data. Proportions of 

 1 were replaced by n-'A divided 

 by n . The fitted model accounted 

 for 85.99r of variance in the data. 

 The smaller peak occurred 3 d af- 

 ter the new moon, and the larger 

 peak 6d after the full moon. 



No simple pattern of spawn- 

 ing was apparent from the pro- 

 portion of fish with late migra- 

 tory nucleus or hydrated oocyte 

 stages captured each day, pre- 

 sumably because such a pattern 

 was confounded by the effects of 

 time of day (see next section). 

 As postovulatory follicles prob- 

 ably persist for a day, and maybe 

 longer in other species (Hunter 

 & Goldberg 1980, Hunter et al. 

 1986), their detection does not 

 depend on the time of day of 

 sampling. 



Diel periodicity in 

 spawning activity 



The November-December 1982 

 samples were also examined for 

 evidence of diel periodicity in 

 spawning. Only mature fish 



