FISHERY BULLETIN: VOL. 86, NO. 2 



April through September, although the percent- 

 age of POF relative to the total number of oocytes 

 was always small (<5%). 



The histological appearance of the zona radiata 

 and follicle layers changed as the oocytes devel- 

 oped. The zona radiata (chorion) was thin and 

 nonstriated in perinucleolar and cortical alveoli 

 oocytes. The zona radiata started to take on its 

 characteristic striated appearance when oocytes 

 reached the yolk granular stage and became no- 

 ticeably thicker and more striated as oocytes 

 grew into the yolk globular stage. In contrast, the 

 granulosa and thecal layers appeared to decrease 

 in thickness as oocyte development proceeded. 

 Oocytes in the perinucleolar and cortical alveoli 

 stages had thick, well-developed granulosa and 

 thecal layers. In yolk granular and yolk globular 

 oocytes, both follicle layers were noticeably thin- 

 ner and the thecal layer was not always continu- 

 ous around the oocyte. 



Frequency distributions of growing oocytes (di- 

 ameters in Gilson's solution >80 fxm; perinucle- 

 olar to hydrated stage oocytes) from ovaries of 48 

 fish were analyzed, and Figure 5 shows typical 

 patterns in fish from four reproductive stages. In 

 a fish captured in March with developing ovaries, 

 growing and vitellogenic oocytes (oocytes during 

 the phase of active vitellogenin uptake) ranging 

 from 80 to 185 jxm in diameter were present (Fig. 

 5A; 625 oocytes counted). Fish in the mature re- 

 productive stage in which spawning did not ap- 

 pear to be imminent, as indicated by GSI values 

 <4, had growing and vitellogenic oocyte diame- 

 ters ranging from 100 to 320 M-m (Fig. 5B; 556 

 oocytes counted), comprising 21% of the total 

 number of oocytes >30 fxm in the ovary. Fish just 

 prior to spawning, as indicated by GSI values >7, 

 had a distinct batch of oocytes with diameters 



Figure 5. — Frequency distributions of growing oocyte diame- 

 ters O80 p.m) in female spotted seatrout collected from South 

 Texas. Growing oocytes comprised 21% of the total number of 

 oocytes >30 ^.m in the ovary. Oocyte diameter refers to the 

 diameters of oocytes after preservation in Gilson's solution. Fre- 

 quency refers to the percentage of each size of oocyte relative to 

 the total number of oocytes in the subsample. Each graph repre- 

 sents data from a single fish at a different reproductive stage. 

 The arrow at 350 jim indicates the minimum size necessary for 

 final maturation to occur. A. Developing stage in March, 

 GSI = 1.6. B. Mature stage in which spawning is not immi- 

 nent, GSI = 3.7. Fish in this stage were collected from April 

 through the end of September. C. Mature stage just prior to 

 spawning, GSI = 7.4. Fish in this stage were collected from 

 April through the end of September. D. Running ripe stage, 

 GSI = 17.6. Fish in this stage were collected from April through 

 the end of September. 



>350 fxm that were undergoing final oocyte mat- 

 uration (Fig. 5C; 585 oocytes counted). However, 

 there were no other distinct modes of vitellogenic 

 oocytes. In running ripe fish, the batch of large 

 oocytes hydrated to a diameter of 520 ixm or 

 greater (Fig. 5D; 1,110 oocytes counted). The re- 

 sults (Figs. 5A-D) clearly demonstrate that C. 

 nebulosus has a continuous distribution of grow- 

 ing and vitellogenic oocytes. The oocyte frequency 

 distribution of the vitellogenic oocytes <320 \i.vc\ 

 in diameter remaining in running ripe fish ap- 





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80 200 320 440 560 680 

 OOCYTE DIAMETER (nm) 



380 



