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Fishery Bulletin 96(2), 1998 
2 Spawning: Ovary contains advanced yolked oo- 
cytes and evidence of spawning activity (migra- 
tory nucleus or hydrated oocytes or postovulatory 
follicles). Less than 100% of advanced yolked oo- 
cytes are in the a stage of atresia. If >50% of ad- 
vanced yolked oocytes are atretic, early yolked 
oocytes are considered nonatretic. 
Figure 2 
Photomicrographs of southern bluefin tuna, Thunnus maccoyii, ovarian tissue collected from the spawning ground (northeast Indian 
Ocean) between October 1992 and June 1995. (A-E) Transverse sections stained with Harris’s haematoxylin and eosin. (A) advanced 
yolked-stage oocyte; (B) migratory-nucleus-stage oocyte; (C) oocyte in the early stages of hydration with some yolk plates still visible; 
(D) fully yolked oocyte in a stage of a atresia; (E) new postovulatory follicle; (F) hydrated-stage whole oocyte. Bar = 0.1 mm. 
