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Mean oocyte diameters of yolked oocytes (AY through 
MN) were generally larger among fish that had begun 
spawning compared with those that had not released a 
batch (Fig. 4). Ovaries that contained POFs had mean 
yolked oocyte diameters that on average were greater than 
0.44 mm. Yolked oocytes in advancing ovaries with no evi- 
dence of recent spawning (no POFs) averaged less than 
0.44 mm in diameter. Again, most of the ovaries with re- 
sidual chorion material were significantly less developed 
than those with evidence of recent spawning (Fig. 4). 
Occurrence of oocyte atresia 
Of the 75 females examined histologically for the occur- 
rence of atresia, only 15 (20%) had ovaries containing 
a-atretic AY, MN, or HY oocytes (Table 4). Within each 
of these 15 females, the average proportion of a-atretic 
AY-HY oocytes among all AY-HY oocytes was 0.034. Thus, 
among all females examined including those with no 
atresia (n= 75), the relative frequency of a-atretic AY-HY 
oocytes among normal AY-HY oocytes was less than 1%. 
The occurrence of atretic AY-HY oocytes as well as atretic 
PY oocytes was higher among females that were either 
close to spawning or partially spawned compared with 
those in a prespawning condition (Table 4). As shown 
with the oocyte distribution plots, normal PY oocytes were 
more common among females that were in a prespawning 
condition. Lower frequencies of normal PY oocytes, but 
higher proportions of atretic PY oocytes among females 
that were partially spawned or close to spawning, indi- 
cated that many PY oocytes do not develop after spawning 
is initiated. We observed no cases of major atresia (>50% 
atretic) among advancing oocytes for all ovaries examined 
histologically. Given the low occurrence of oocyte atresia, 
we assumed a negligible effect of atresia on estimates of 
annual fecundity. 
