84 
Fishery Bulletin 109(1) 
10 
□ YG mm YG(LC) 
=1 MN(E) 
□ MN(L)[min] HD 
17 h A 
k 
1 h B 
9 h C 
17 h D 
900 
Oocyte diameter (pm) 
Figure 2 
Temporal changes in the frequency dis- 
tribution of oocyte diameter at different 
developmental stages of Japanese flounder 
( Paralichthys olivaceus). Data are from suc- 
cessive samples of oocytes from fish no. 2, 
30 May-1 June 2005 (see Table 2 and Fig. 
3A). (A) on 30 May, and (B-D) on 31 May. 
HD = oocyte at hydrated stage; MN(L) = at late 
migratory nucleus stage; MN(E) = at early 
migratory nucleus stage; YG(LC)=the lead- 
ing cohort of oocytes at yolk granule stage; 
and YG=yolk granule stage. 
iooo r 
800 - 
E 700 
3 
® 600 
<u 
E 
.5 500 
□ □ 
• YG(LC) 
OMN(E) 
AMN(L) 
O HD 
□ OV 
12 
12 
Figure 3 
Diurnal changes in oocyte diameters at each developmental stage 
for individual Japanese flounder (Paralichthys olivaceus). (A) 
Experiment for fish no. 2, conducted between 30 May and 1 
June in 2005 at 11.3°C. (B) Experiment for fish no. 3, conducted 
between 20 and 22 July in 2005 at 16.9°C. Bars indicate standard 
deviation. The slopes of regression lines for HD-stage oocytes 
represent the growth rate of hydrated oocytes. OV=ovulated egg; 
HD = oocyte at hydrated stage; MN(L) = at late migratory nucleus 
stage; MN(E) = at early migratory nucleus stage; and YG(LC) = 
the leading cohort of oocytes at the yolk granule stage. 
mm, 11.2<T<16.9°C, n= 6: Table 2) by ANCOVA. We 
could not examine the effect of other females because 
the overlap of temperature was narrow. 
In five out of ten 48-h experiments, final maturation 
processes were observed twice at about 24-h interval 
(Figs. 2 and 3). In the other five 48-h experiments, the 
final maturation process occurred only once on the first 
day of each experiment. Once a batch of oocytes entered 
the final maturation process, these oocytes completed 
final maturation to be ovulated. 
Although females spawned naturally in the tank for 
their spawning periods of 2-3 months, they could not 
spawn naturally during the 48-h experiments. They 
could only ovulate oocytes into their ovarian cavity. 
Duration of each spawning marker 
Results 
Experiments 
The growth rates of oocytes at MN(L), MN(E), and 
YG(LC) stages were slow, whereas the growth rate of 
HD-stage oocytes was rapid (Fig. 3). At the lower tem- 
perature, HD- and MN-stage oocytes, or MN(L)- and 
MN(E)-stage oocytes coexisted, indicating that the two 
batches of oocytes entered the final maturation process 
at the same time (Figs. 2 and 3). 
The duration of each spawning marker changed consid- 
erably with temperature. The durations of oocytes at 
the MN(E) and MN(L) stages, and POF(new) decreased 
exponentially from 24 to 3 h, 16 to 4 h, and 16 to 4 h, 
respectively, for the established temperature ranges (9.2° 
or 11.3° to 22.6°C; Fig. 4). Duration of these markers 
decreased by a factor of 0.16, 0.36, 0.31, respectively, as 
temperature increased by 10°C (Table 3). 
The growth rate of hydrated oocyte diameter ( G HD , 
in pm/h) increased exponentially as temperature (T) 
increased (Fig. 5) as follows: 
