McDermott and Lowe: Reproductive cycle and sexual maturity of Pleurogrammus monopterygius 
331 
the formation of cortical alveoli, followed by oil drop- 
lets, yolk accumulation, nuclear migration, and hy- 
dration (Fig. 2). The appearance of oil droplets after 
the formation of cortical alveoli and the coalescence 
of yolk before or during nuclear migration are fea- 
tures that have also been described for masked green- 
ling (Munehara et ah, 1987). Another feature that is 
similar to the masked greenling is that hydrated 
atretic oocytes were reabsorbed very slowly and could 
be found in the ovary for over 1 year. 
The early maturation of the Atka mackerel ovary 
is characterized by an accumulation of oil droplets 
in the developing oocytes with a gradual increase in 
oocyte size over several months from January until 
May. Vitellogenesis is completed within 1 month, 
similar to the duration of vitellogenesis in masked 
greenling, but uncommonly short for most subarctic 
fishes (Munehara and Shimazaki, 1989). 
The spawning period for Atka mackerel is extended 
and can last up to 4 months, from July through Oc- 
tober. This relatively long spawn- 
ing period can be attributed to 
the duration of time spent be- 
tween the spawning of indi- 
vidual batches. Zolotov (1993) 
stated that the greater number 
of batches and the longer inter- 
val between their spawning cor- 
responds to the longer duration 
of the reproductive period of 
Atka mackerel as compared 
with the arabesque greenling 
( Pleurogrammus azonus). The 
average spawning duration of 3 
months found in this study is in 
agreement with the spawning 
duration reported for Atka 
mackerel in Kamchatka waters 
(Zolotov, 1993). However, the 
beginning of spawning in Alaska 
waters was observed in July last- 
ing until October, whereas the 
spawning period in Kamchatka 
waters was described as start- 
ing in June and lasting until Sep- 
tember (Zolotov, 1993). These dif- 
ferences may be attributed to 
year-to-year variations; however, 
different oceanographic condi- 
tions in Alaska versus Kam- 
chatka waters may also be a 
contributing factor. There are 
not enough data to substantiate 
a seasonal cline in the timing of 
the reproductive cycle ranging 
from Kamchatkan waters to the 
Gulf of Alaska. The observation 
of a few spawning fish in March 
and April indicates that spawn- 
ing times may be more variable 
than previously assumed. Data 
from several years were pooled 
in this study as the number of 
samples was insufficient to dis- 
tinguish annual differences. 
0 
3 
03 
E 
c 
o 
o 
Q. 
O 
CL 
1 1.5 2 2.5 3 3.5 4 4 5 5 5.5 6 6 5 7 7.5 8 8 5 9 9 5 10 
Age (yr) 
Figure 6 
Age at maturity (all geographical areas pooled) for Atka mackerel. 
