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Fishery Bulletin 96(2), 1 998 
males was determined by estimating the incidence 
of fish with postovulatory follicles (POF) (Hunter and 
Goldberg, 1980). These structures were classified as 
day-0, day-1, or day-2 postovulatory follicles, following 
the description by Goldberg et al. (1984) for Sardinops 
sagax and by Melo (1994) for Engraulis capensis. 
38°S 
39° 
40° 
41 ° W 
Figure 1 
Location where samples of female striped weakfish were 
collected off “El Rincon” area. 
The proportion of spawning females was estimated 
from the different stages of POF, but the spawning 
frequency was determinated by taking the average 
of the percentages of day-0 and day-1 spawning fe- 
males (Fitzhugh et al., 1993). 
Batch fecundity (BF) (number of oocytes released 
per spawning) was estimated gravimetrically with 
the hydrated oocyte method (Hunter et al., 1985) on 
fixed ovarian samples. Hydrated ovaries that con- 
tained new postovulatory follicles were not used for 
this estimation. Batch fecundity was determined for 
41 females (17 from “El Rincon” and 24 from the 
Uruguayan coast). Three 0.1-g tissue subsamples 
were collected from the anterior, middle, and poste- 
rior sections of one ovary of each pair. These 
subsamples were weighed to the nearest 0.00001 g. 
All hydrated oocytes in each subsample were counted 
under stereoscopic microscope (magnification of 6x). 
Batch fecundity for each female was the product of 
the mean number of hydrated oocytes per unit weight 
and the total weight of the ovaries. Relative fecun- 
dity (RF) (hydrated oocytes per gram of body weight) 
was calculated as the batch fecundity divided by fe- 
male weight (without ovary). To compare the “El 
Rincon” data with those from the Uruguayan coast, 
the length ranges coincident with the two zones were 
truncated between 40 and 50 cm TL (“El Rincon,” 
n= 15; Uruguayan coast, n= 17). The fecundity val- 
ues and the coefficients of the batch fecundity to 
Table 1 
Morphological changes observed in the different oocyte growth phases. Adapted from Forberg (1982). 
Oocyte growth stages 
Description 
First growth phase 
Cromatin nucleolus stage 
Early nucleolus stage 
Late nucleolus stage 
Previtellogenic oocytes with diameters smaller than 100 pm. Cytoplasm is basophilic and the 
nucleus shows a number of nucleoli situated peripherally. Follicular cells are flattened and 
become visible on the outer surface of oocyte. 
Second growth phase 
Yolk vesicle stage 
Diameter ranged between 100-250 pm. Cytoplasm is basophilic and shows small uncolored 
vacuoles (yolk vesicles). Granulosa and follicular thecae are distinguished and the zona 
radiata becomes visible around the periphery of oocyte. 
Primary yolk stage 
Diameter ranged between 250 and 350 pm. Numerous eosinophilic yolk globules appear 
between the yolk vesicles. These yolk globules are composed mainly of proteins. The zona 
radiata and the follicle epithelium are more prominent. 
Secondary yolk stage 
Diameter between 400 and 600 pm. The yolk globules have multiplied and increased in size, 
occupying all the cytoplasm. The nucleus exhibits an irregular shape, and the zona radiata 
increases in thickness. 
Tertiary yolk stage or final 
oocyte maturation 
Oocyte diameter ranged between 600 and 700 pm. In the first instance, the nucleus is 
displaced to the animal pole (migratory nucleus stage). The nuclear membrane disintegrates 
and the yolk globules tend to coalesce. In the section, these oocytes appear with a cytoplasm 
weakly eosinophilic and an irregular shape. 
