FISHERY BULLETIN: VOL. 81, NO. 2 



"Balbiani bodies." While the function of these re- 

 mains unknown, Guraya (1979) has suggested that 

 they act as centers for the formation, multiplication, 

 and accumulation of organelles and materials needed 

 for yolk deposition. 



The mean diameter of resting oocytes increased 

 from October to December, remained fairly constant 

 from December to April, and then declined from 

 April through June. The increase was presumably 

 caused by progressively older, and therefore larger, 

 early perinucleolus oocytes entering the resting 

 stage. The decline in mean size seen during the 

 spring was probably due to the larger ones having 

 been transformed into late perinucleolus oocytes. 



Resting oocytes rapidly declined in abundance 

 from May to June and were absent by July. Coinci- 

 dent with this decline was an increase in late perinu- 

 cleolus oocytes. This observation, combined with 

 their similarities in mean size and overlapping size- 

 frequency distributions, indicates that resting oo- 

 cytes were transformed into late perinucleolus 

 oocytes. During this transformation the zonation in 

 the cytoplasm was lost, the number of nucleoli in- 

 creased, and the cytoplasm became less basophilic. 



The vitellogenic phase of oogenesis contains the 

 early and late maturing types as well as hyaline 

 oocytes. It begins as the late perinucleolus oocytes 

 develop into early maturing oocytes. As indicated by 

 their relative changes in seasonal abundance and 

 size-frequency distributions, this changeover occurs 

 primarily during the late spring and summer months. 

 In large late perinucleolus oocytes a ring of vacuole- 

 like structures is seen near the periphery of the 

 cytoplasm. Oocytes of this type have alternatively 

 been described as yolk vesicle (Yamamoto 1956a; 

 Khoo 1979), early or primary vitellogenic (Monaco et 

 al. 1978; Htun-Han 1978) or vacuolated (James 

 1946) oocytes. This stage marks the beginning of 

 vitellogenesis during which the oocyte rapidly grows 

 in size and accumulates yolk. Yolk vesicles apparent- 

 ly originate from the Golgi complexes (Yamamoto 

 and Onozata 1965; Yamamoto and Oota 1967) and 

 contain mucopolysaccharides which represent the 

 first form of yolk inclusions (Yamamoto 1956a; 

 Malone and Hisaoka 1963; Khoo 1979). Yamamoto 

 (1956c) and Khoo (1979) have reported that in the 

 later stages of vitellogenesis the yolk vesicles are dis- 

 placed to the periphery of the oocyte and gave rise to 

 the cortical alveoli which, after fertilization, con- 

 tribute to water hardening of the egg. Simultaneous 

 with the appearance of these vesicles the beginning 

 of the zona radiata was seen between the follicle cells 

 and the cytoplasm. As early maturing oocytes con- 

 tinued to develop, yolk globules became in- 



352 



terspersed with the yolk vesicles near the periphery 

 of the cytoplasm. These globules represented the 

 second form of yolk inclusions which have been 

 shown in other species to contain proteins, phospho- 

 lipids, and fats (Yamamoto 1957; Khoo 1979). 



As yolk continued to accumulate toward the nu- 

 cleus the mean diameter of early maturing oocytes 

 continued to increase. The significant decrease in 

 mean diameter of this stage noted from September to 

 October was due to the larger early maturing oocytes 

 being classified as late maturing. This is demon- 

 strated in their size-frequency distributions where it 

 can be seen that size classes formerly dominated by 

 early maturing oocytes had become predominantly 

 late maturing oocytes. As expected, the percentages 

 of early maturing oocytes declined as the percent- 

 ages of late maturing oocytes increased. Following this 

 transformation, mean oocyte diameter increased 

 rapidly. 



Beginning in April late maturing oocytes began to 

 be transformed into hyaline oocytes preparatory to 

 their release from the follicle. At this time the yolk 

 globules began to break open allowing the yolk to 

 coalesce. Accompanying this was an increase in size, 

 presumably due to the absorption of fluid, which 

 caused the zona radiata to become thin. 



The low percentage of hyaline oocytes observed is 

 an indication that spawning is intermittent during the 

 breeding season, with only a portion of the late 

 maturing oocytes taking in fluid and being dis- 

 charged at one time. Following the expulsion of the 

 ripe ovum, the remaining follicle collapses into an 

 irregular mass, decreases in size, and disappears 

 shortly after spawning. 



The year-round presence of some oogonia and early 

 perinucleolus oocytes indicates that a small amount 

 of oogonia production and subsequent development 

 into early perinucleolus oocytes occur throughout 

 the year. Although not established, it is assumed that 

 those early perinucleolus oocytes produced during 

 the late fall and winter enter the resting stage until 

 the following spring. Small percentages of late 

 perinucleolus and early maturing oocytes were also 

 present year-round. The small percentage of late 

 perinucleolus oocytes from October through January 

 indicates that not all of them had developed into ear- 

 ly maturing oocytes over the late spring and summer 

 months. Presumably these would have begun to ac- 

 cumulate yolk during the late fall and early winter 

 months. This would account for the small percent- 

 ages of early maturing oocytes seen at this time. 



The percentages of the two types of regressing 

 oocytes were very small. Corpora atretica (Regress- 

 ing Type I) were seen only in prespawning fish, and 



