Cuellar et al Reproductive seasonality, maturation, fecundity, and spawning frequency of the vermilion snapper 



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Figure 3 



Photographs of histological section of the ovary of vermilion snapper, showing (A) new 

 postovulatory follicle (POF) at lOOx, in which the columnar granulosa cells with prominent 

 nuclei are distinct and the lumen is visible, and i B ) old POF at 400x with a typical triangular 

 shape, in which most of the granulosa cells without nuclei are disintegrating. (g=granulosa 

 layer, t=thecal layer. l=lumen) 



y-stained structures with approximately half to very 

 few of the granulosa cells intact ( Fig. 3B ). Old POF's 

 resembled 1-day-old POF's of Engraulis mordax 

 (Hunter and Macewicz, 1985). To confirm temporal 

 trends in the occurrence of hydrated females, the 

 samples collected for this study were supplemented 

 with additional histological slides (from spawning 

 females collected on MARMAP research cruises in 

 1991 and June to August 1993) for examination of 

 POF age. 



To calculate spawning frequency, the method of 

 Fitzhugh et al. (1993) was used to calculate overall 

 percentages of HO's, new POF's, and old POF's. A 

 proportion was computed for each category by divid- 

 ing the total number observed in each category by 

 the total number of mature females. An overall av- 

 erage was computed by summing the three category 

 proportions and by dividing by three. The overall 

 average was then multiplied by number of days in 

 the spawning season to determine spawning fre- 

 quency. We defined the spawning season as the date 

 ( 15 April 1992) when spawning condition was histo- 

 logically evident until the date (24 September 1992) 

 when major atresia of AYO's first occurred. If the 

 proportions for each criterion were independent of 

 those of other criteria and similarly distributed, then 

 they could be combined to increase the sample size 

 (Alheit et al., 1984). If spawning frequencies are to 

 be combined, they must not be statistically differ- 

 ent; therefore, we used the Mann-Whitney test to 

 examine differences between frequencies of the HO's 



versus new POF's and between new POF's versus 

 old POF's. 



Results 



Sex ratio, ovarian development, maturity, 

 and spawning season 



Vermilion snapper did not exhibit a 1:1 sex ratio; fe- 

 males were 63% of the samples (Table 5). Compari- 

 sons of sex ratio by 5-cm length classes revealed sig- 

 nificant differences from a 1:1 ratio for every length 

 class. Trap and hook-and-line samples collected dur- 

 ing MARMAP cruises and samples collected by the 

 commercial hook-and-line fishery yielded similar sex 

 ratios. The sex ratio from Grimes ( 1976) was compa- 

 rable to the sex ratio for all samples of vermilion 

 snapper in this study. 



Oocyte size-frequency (percent) distributions for 

 five oocyte stages (Fig. 4) revealed the developmen- 

 tal sequence of ovary maturation. Oocyte size was 

 correlated with stage of development; however, there 

 was considerable overlap in size between stages. This 

 asynchronous pattern of development means that the 

 number of batches cannot be inferred from the size- 

 frequency distribution of oocytes. 



The mean oocyte diameter (MOD) appeared con- 

 stant over the spawning season (Fig. 5). This is evi- 

 dence that oocytes matured and were developing 

 throughout the spawning season. 



