Bowers: Reproductive cycle of oocytes and embryos of Sebastes flavidus 



233 



Table 2 



Classification and temporal occurrence of oocytes from Sebastes flatiidus collected off central California, based on histological appearance. 

 See text for additional histological descriptions. 



Stage 



Major histological characteristics 



Temporal occurrence 



I Oogonia 



II Early perinucleolus 



III Late perinucleolus 



IV Initial yolk accumulation 



V Final yolk accumulation 



VI Migratory nucleus 



VII Ovulation & Fertilization 



Small cells (5-25f/) found in clumps or "nests." Cytoplasm pale to All year 



clear. Basophilic nucleus occupying most of cell volume. 



Wide range of cell diameters (20-lOOfi). Intense basophilic cytoplasm. All year 



One or two large nucleoli in nucleus. 



Diameters 50-140(i. Small, clear vesicles present in cytoplasm. Feb. -Oct. 



Cytoplasm pale-blue to light-gray. Several small nucleoli around inner 

 margins of nuclear membrane. 



Cell diameters 120-210ti. Small spherical, eosinophilic yolk granules in July-Oct. 



a distinct cortical zone in cytoplasm. Cytoplasm vesicular and light- 

 gray. Well-developed follicle surrounds a developing vitelline mem- 

 brane. Several small nucleoli around the inner margins of nuclear 

 membrane. 



Large cells (200-600 jj). Cell volume one-half to entirely full of yolk Sept. -March 



spheres. Lampbrush chromosomes visible in nucleoplasm. Lipid 

 vacuoles appear larger as they coalesce. 



Cell diameters 600-750 ^i. A single, large lipid vacuole present. Dec. -March 



Nuclear membrane indistinct or absent. Nuclear material irregularly 

 shaped and no longer centrally located. Follicle may be distorted and 

 irregularly shaped. 



Mature oocyte free from follicle. The yolk mass is a single, large Dec-March 



homogeneous mass, staining deep-purple. In fresh (unfixed) ovaries, 

 ova appear clear or translucent. 



Results 



Oocyte development 



Major histological characteristics distinguishing stages 

 for S. flavidus are listed in Table 2. All cells could be 

 categorized into one of the seven stages. Terminology 

 and nomenclature follow Moser (1967a) and Howell 

 (1983). 



Stage I: Oogonia These small cells were 5-25^ in 

 diameter and were found in clumps or "nests" along 

 the lamellar branches (Figs. lA, 4E). Larger oogonia 

 in the 20 fi range possessed a deeply-stained chromatin 

 network attached to a single, large basophilic nucleolus. 



Stage II: Early perinucleolus These oocytes were 

 20-100^ in cell diameter. While still closely associated 

 with neighboring oogonia, there was noticeable move- 

 ment away from oogonial nests. The most obvious 

 feature of this cell was the intensely basophilic cyto- 

 plasm (Figs. IB, 4E). 



Stage III: Late perinucleolus Diameters were 50- 

 140^. Clear vacuoles appeared in the cytoplasm of 

 oocytes as small as 50 ^i. Initially these vacuoles were 

 distributed as a poorly organized ring surrounding the 



nucleus, but were seen randomly scattered throughout 

 the cytoplasm of larger oocj^es (Figs. IB, 4E). As 

 growth continued, they increased in size and number. 



Stage IV: Initial yolk accumulation The earliest 

 signs of yolk accumulation were seen in oocytes of 

 120-210 p< in diameter. Small, spherical globules of yolk 

 were seen in a distinct cortical zone in the cytoplasm 

 (Fig. 1C,D). The follicle enclosing the oocyte is more 

 complex and composed of several identifiable struc- 

 tures (see below). 



Stage V: Final yolk accumulation To simplify the 

 staging of yolked oocytes, cells with approximately one- 

 half their volume filled with yolk spheres, and cells 

 whose volumes were entirely filled with yolk, were 

 placed in Stage V. Yolk spheres increased in number 

 and size. By the end of this stage, the cell diameter in- 

 creased to about 650 fi. The cytoplasm was entirely 

 filled writh yolk spheres of various sizes (Fig. 2A). The 

 vacuoles which were distributed throughout the cyto- 

 plasm began to coalesce, forming larger vacuoles. 



An eosinophilic nucleoplasm with lampbrush chromo- 

 somes was visible (Fig. 2B). In the late Stage-V cell, 

 the nucleus became irregularly shaped and the nuclear 

 membrane was often indistinct (Fig. 2A). 



