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



639 



between the nucleus and the zona pellu- 

 cida (egg diameter ~0. 15-0.25 mm) 



Stage 2 Lightly packed yolk possibly extending 

 from the periphery to the nucleus with the 

 nuclear area still evident (-0.25-0. 35 

 mm) 



Stage 3 Yolk dense enough to occlude the nucleus 

 (~0.35-0.45 mm) 



Stage 4 Parts of the dense yolk become translu- 

 cent usually beginning at the periphery 

 (-0.45-0. 60 mm) 



Stage 5 Oocyte is translucent except for the oil 

 droplet (-0.60-1.25 mm). 



Alpha-atretic AYO's were not included in TF estimates. 

 To estimate total fecundity, whole oocytes were 

 examined by using a modified version of the hydrated 

 oocyte method of Hunter et al. (1985). Each sample 

 weighed approximately 50 mg and consisted of about 

 100 to 150 oocytes. Three diameter measurements 

 per oocyte were taken and then averaged to obtain a 

 mean oocyte diameter (MOD). A mean of the MOD's 

 of all AYO's in the two samples taken from each fe- 

 male was calculated for 138 females and then ana- 

 lyzed for TF. Oocytes on each gridded slide were 

 counted, measured, and staged with GLOBAL LAB 

 image analysis software linked by a video camera 

 system to a compound microscope. The following fe- 

 cundity equation was used to assess TF: 



TF = ZxC, 



where Z = ovary weight in grams, and 



C = oocyte density (number of AYO's per 

 gram of ovarian tissue). 



To see if time had an impact on TF, TF was regressed 

 on OFWT and on days elapsed since 15 April. Also, 

 an ANCOVA was performed on monthly TF regres- 

 sion equations to see if there was a temporal effect 

 onTF. 



To see if atresia had any effect on fecundity esti- 

 mates, the proportion of atretic oocytes was calcu- 

 lated for each whole oocyte sample that was counted. 

 The number of alpha atretic AYO's in a sample was 

 divided by the total number of AYO's in that sample 

 (Hunter etal., 1992). Atresia subclasses were defined 

 by Bretschneider and Duyvene de Wit (1947) and 

 Hunter and Macewicz ( 1985 ). Alpha atresia involves 

 the reabsorption of the entire oocyte, and beta atre- 

 sia involves the major degeneration and reabsorp- 

 tion of the follicle (Hunter and Macewicz, 1985). 

 Three subclasses of alpha atretic AYO's were noted: 

 no atresia, minor atresia ( 1-49%), and major atresia 

 (50-100%). 



To estimate PF, only females from the beginning 

 of the spawning season that showed no recent signs 

 of spawning (presence of HO's or POF's) were used 

 in analyses. Because PF is estimated at the begin- 

 ning of the season, some oocytes may not have yet 

 been recruited into the stock of advanced yolked oo- 

 cytes. To find the size at which oocytes are fully re- 

 cruited, a series of stepwise multiple regressions was 

 run on 59 females (Table 3). Data were removed by 

 0.005 mm increments beginning with the lowest di- 

 ameter class of 0.360 mm. Analysis indicated that 

 the threshold for a significant effect of diameter on 

 PF occurred between 0.445 mm and 0.450 mm. The 

 regression coefficient for oocyte diameter was signifi- 

 cant for females with a MOD equal to or less than 

 0.445 mm but insignificant for females with a MOD 



Figure 2 



Photographs of whole oocytes of vermilion snapper at 40*: (A) stage-3 advanced yolked oocyte (AYO), in which 

 the oocyte is completely opaque except the peri vitelline border; (B) late migratory nucleus-stage oocyte (MNOi, 

 in which some droplets of the peripheral yolk have coalesced and become translucent: and (Cl hydrated oocyte 

 (HO), in which the whole oocyte is translucent. 



