Bowers: Reproductive cycle of oocytes and embryos of Sebastes flavidus 



239 



hatched embryos (larvae) been collected in the field, 

 they would have been included in this stage. Larvae 

 were, however, taken from females held in the labora- 

 tory. These larvae were 4-6 mm in length and had open 

 mouths with functional jaws. The yolk mass appeared 

 to be reduced, and liver tissue was associated with a 

 persistent oil globule (Fig. 4C). 



Seasonal oocyte cycle Oogonial nests were observed 

 in all samples, with about 25% frequency of occurrence 

 throughout the entire reproductive cycle (Fig. 5). These 

 Stage-I cells were most conspicuous early in the repro- 

 ductive season and in ovaries of spent females. 



Stage II or early-perinucleolus oocytes were also 

 noted year-round and accounted for about one-third of 

 all oocyte types observed (Fig. 5). The large nucleoH 

 and dark cytoplasm were features that easily distin- 

 guish this stage. Mid- to late Stage-II cells were ob- 

 served either singly or in groups around oocytes of later 

 maturational stages (Stages III- VII) and were con- 

 sidered the 'resting' stage oocytes of other investi- 

 gators (Bowers and Holliday 1961, Howell 1983). 



In early spring, a broader range of Stage-II cell 

 diameters was evident, indicating continued oocyte 

 growth. Stage-Ill cells rapidly increased during March 

 and April to a maximum frequency of 40% in April, 

 and decreased in frequency by August as this clutch 

 of oocytes developed (Fig. 5). 



Copulation of yellowtail rockfish typically occurs over 

 three months beginning in August and ending in Octo- 

 ber (Eldridge et al. 1991). The incidence and frequency 

 of sperm in yellowtail rockfish ovaries were not evalu- 

 ated in this study. However, small clumps or 'packages' 

 of sperm were occasionally seen closely associated with 

 the stroma or in spaces between developing (yolked) 

 oocytes. 



Initial yolk accumulation (Stage IV) was first docu- 

 mented in females collected in July, with all specimens 

 collected in August showing this stage. In August, 34% 

 of oocytes were Stage IV. Oocytes of Stage IV ap- 

 peared as grape-like clusters on the outer margins 

 of the lamellar branches, developing in a group- 

 synchronous manner (Fig. IC). The occurrence of 

 Stage-IV oocytes sharply declined from August to 

 November when no Stage-IV oocytes were observed 

 (Fig. 5). As yolk accumulation continued, yolk spheres 

 increased in size and number, filling the cytoplasm to 

 about one-half its volume. At this point, oocytes were 

 categorized as Stage V. Stage V was the most ad- 

 vanced oocyte observed from its first appearance in 

 September until December when the frequency de- 

 clined (Fig. 5). Oocytes in this developmental stage 

 were most prevalent in November when they accounted 

 for a mean of 48% of all oocytes. Stage-VI (Migratory 

 nucleus) oocytes were first observed in December. 



so 



25 





 50- 



25 



0- 

 50- 



§ 25- 

 o 



STAGE I 



— 1 1 r 



'-'-• *\.^* 



T 1 1 1 1 1 1 



STAGE II 

 *— » 



+ + 



— I 1 1 1 r 



STAGE I 



---i. 



N^.-> 



- + 



-f f 



50 

 25- 



.i-i- 



-4— f- 



/-\ STAGE V 



* + - 



, , , s 



MJJASONDJFMA 

 MONTH 



Figure 5 



Mean monthly frequency distributions of oocyte 

 Stages I-VI in ovaries oi Sebastes flavidus during 

 1985-86. Error bars represent 1 SE. Plus signs = 

 present, minus = not present. Monthly sample size 

 same as in Table 1. 



Ovaries with an advanced mode of Stage-VI oocytes 

 continued to be collected over the next 3 months 

 (January-March). This stage appeared to have a short 

 duration, as ovaries containing Stage VII were also 

 collected in some of the same months as Stage VI 

 (December-February). 



Ovary maturation was determined by using the most 

 advanced oocyte or embryonic stage present in each 

 monthly sample, and their frequency of occurrence was 

 expressed as percent(s) (Fig. 6). Temporal ovarian 

 development is illustrated and reflects a prolonged 

 reproductive season. 



While accurate frequency distributions on Stage- VII 

 oocytes were not possible, the peak month of ovulation 

 and fertilization appeared to be February. Sections of 

 samples with Stage-VII oocytes showed eggs free from 

 (e.g., outside) their follicular remnants. While continu- 

 ity of follicular components (theca and granulosa) was 

 disrupted, the integrity of the capillary network was 

 maintained and there was a close association with the 

 developing embryo. 



Ovaries recently spawned (parturition) were seen as 

 early as January and most frequently collected in 

 March (Fig. 6). The ovary was greatly reduced in size, 



