Barbieri et al.: Maturity, spawning, and ovarian cycle of Micropogonias undulatus 



677 



July 



QSI = 12.7 % 

 n = 512 



"hftihJliTK 



October 



GSI = 9 68 % 

 n = 445 



iTTkffMlllti 



0.1 0.2 0.3 0.4 



16 





August 



GSI = 12 5% 

 n = 616 



MfcJk 



November 



GSI = 6.8 % 



n = 448 



MU 



tu 



1 0.2 0.3 0.4 0.5 



September 



GSI = 7.06 % 



n = 491 



TJlkMllL 



December 



GSI = 5 9 % 

 n = 533 



2 3 0.4 0.5 



2 3 4 0.5 



Oocyte diameter (mm) 



Figure 5 



Monthly oocyte diameter distributions during the spawning sea- 

 son of Atlantic croaker, Micropogonias undulatus, in the Chesa- 

 peake Bay and adjacent coastal waters. Each panel represents 

 one female in the fully developed gonad stage. Samples from July 

 to October are from Chesapeake Bay; samples from November to 

 December are from coastal waters off Virginia and North Caro- 

 lina. GSI=gonadosomatic index; «=number of oocytes measured. 



males. No POF's were found in fully developed fe- 

 males, even those with left-over hydrated oocytes in 

 the posterior end of the ovarian lumen. As a result, 

 it was usually impossible to distinguish fully devel- 

 oped females spawning for the first time from those 

 that had spawned at least once before (partially spent 

 females). 



Atresia of advanced yolked oocytes 



Spawning-phase Atlantic croaker females (gonad 

 stages 3-5; Table 1) showed a high incidence of a 

 atresia of advanced yolked oocytes throughout the 

 spawning season (July-December). However, the 

 exact proportion of atretic oocytes could not be de- 

 termined because of the difficulty in identifying oo- 

 cytes in very early stages of atresia. Some females 



showed healthy advanced yolked oocytes, 

 atretic advanced yolked oocytes in different 

 stages of degeneration, and atretic follicles 

 (p-, Y"> an d 8-stage atresia) in the same 

 ovary. 



Compared with healthy oocytes (Fig. 6A), 

 early phases of a atresia of advanced yolked 

 oocytes in Atlantic croaker are character- 

 ized by the disintegration of the nucleus, 

 which loses its integrity, becoming amor- 

 phous and slightly basophilic, and by the 

 disintegration of yolk globules, which be- 

 gin to dissolve, forming a continuous, amor- 

 phous mass, especially around the nucleus 

 (Fig. 6B). At this stage, the majority of yolk 

 granules at the periphery of the cytoplasm 

 still maintain their structural integrity, 

 spherical shape, and strong acidophilic 

 staining. At intermediate stages, disintegra- 

 tion of yolk globules progresses towards the 

 peripheral cytoplasm, which by now may 

 have a band of dark, basophilic material 

 ( Fig. 6C ), and the zona radiata begins to de- 

 teriorate. At late stages of a atresia (Fig. 

 6D), the nucleus has completely disap- 

 peared, the zona radiata has lost its struc- 

 tural integrity, and the cytoplasm has been 

 invaded by phagocytizing granulosa cells. 

 Only portions of dissolved yolk and a few 

 yolk globules remain at this stage. However, 

 atresia will continue until the oocyte is com- 

 pletely resorbed, leaving only the remain- 

 ing follicle. After this phase, a-stage atresia 

 has been completed and follicular atresia 

 begins with the resorption of the remain- 

 ing granulosa and thecal cells. 



Comparisons of fresh oocyte samples with 

 histology slides confirmed the high inci- 

 dence of a atresia of advanced yolked oocytes in At- 

 lantic croaker. Although the histological method ap- 

 peared more sensitive in detecting earlier stages of 

 atresia (Fig. 7A), the use of fresh oocytes was indis- 

 pensable. Fresh oocytes provided an easy, fast way 

 to assess gonad condition and to identify oocyte 

 atresia. A large proportion of atretic advanced yolked 

 oocytes could be easily identified by clumping and 

 darkening of the yolk granules, formation of a clear 

 zone in the peripheral cytoplasm (Fig. 7B), and at 

 later stages, formation of several light yellow vacu- 

 oles (Fig. 7C). 



Description of the ovarian cycle 



A diagrammatic representation of the Atlantic 

 croaker ovarian cycle, based on the temporal distri- 



