79 
Abstract — The duration of spawn- 
ing markers (e.g. signs of previous 
or imminent spawnings) is essential 
information for estimating spawning 
frequency of fish. In this study, the 
effect of temperature on the duration 
of spawning markers (i.e., oocytes at 
early migratory nucleus, late migra- 
tory nucleus, and hydrated stages, as 
well as new postovulatory follicles) 
of an indeterminate multiple-batch 
spawner, Japanese flounder (Par-a- 
liclithys olivaceus), was evaluated. 
Cannulation was performed to remove 
samples of oocytes, eggs, and postovu- 
latory follicles in individual females at 
2-4 hour intervals over 27—48 hours. 
The duration of spawning markers 
was successfully evaluated in 14 trials 
ranging between 9.2° and 22.6°C for 
six females (total length 484-730 
mm). The durations of spawning 
markers decreased exponentially 
with temperature and were seen to 
decrease by a factor of 0.16, 0.36, 0.30, 
and 0.31 as temperature increased by 
10°C for oocytes at early migratory 
nucleus, late migratory nucleus, and 
hydrated stages, and new postovula- 
tory follicles, respectively. Thus, tem- 
perature should be considered when 
estimating spawning frequency from 
these spawning markers, especially 
for those fish that do not spawn syn- 
chronously in the population. 
Manuscript submitted 7 May 2010. 
Manuscript accepted 27 October 2010. 
Fish. Bull. 109:79-89 (2011). 
The views and opinions expressed 
or implied in this article are those of the 
author (or authors) and do not necessarily 
reflect the position of the National 
Marine Fisheries Service, NOAA. 
The effect of temperature on the duration 
of spawning markers — migratory-nucleus and 
hydrated oocytes and postovulatory follicles— 
in the multiple-batch spawner Japanese flounder 
( Paralichthys olivaceus) 
Yutaka Kurita (contact author)' 
Yuichiro Fujinami 2 
Masafumi Amano 3 
E-mail address for contact author: kurita@affrc.go.jp 
1 Tohoku National Fisheries Research Institute 
Fisheries Research Agency 
Shinhama 3-27-5 
Shiogama, Miyagi 985-0001, Japan. 
2 Miyako National Center for Stock Enhancement 
Fisheries Research Agency 
Sakiyama, Miyako, Iwate 027-0097, Japan. 
3 School of Marine Biosciences 
Kitasato University 
Ofunato, Iwate 022-0101, Japan. 
Production of eggs in fish populations 
varies spatially and temporally during 
a single spawning season (Scott et al., 
2006; Allain et al., 2007) and inter- 
annually (Kjesbu et al., 1998). These 
variations can be caused by changes 
in temperature, food supply (Somara- 
kis et al., 2004, 2006), fish size com- 
position, and nutritional condition of 
spawners (Motos, 1996; Marteinsdot- 
tir and Begg, 2002; Scott et al., 2006). 
Spatial and temporal variations in 
egg production probably affect repro- 
ductive success (Kjesbu et al., 1996b; 
Wright and Gibb, 2005; Secor, 2007; 
Nishimura et al., 2007; Wright and 
Trippel, 2009). Therefore, it is neces- 
sary to understand the mechanism of 
spatiotemporal variation in egg pro- 
duction at the population level. Based 
on the above cited information, the 
variations in egg production of multi- 
ple-batch spawners can be evaluated 
by using accurate estimates of batch 
fecundity and spawning frequency in 
relation to age, size, and condition. 
Quantification of population egg 
production per day is also essential 
for estimating population size (spawn- 
ing stock biomass [SSB] ) when us- 
ing the daily egg production method 
(DEPM; Parker, 1980; Lasker, 1985). 
DEPM has so far been applied mainly 
to some clupeid fish populations and 
is expected to be applied to other 
fish species including demersal fish 
(Stratoudakis et al., 2006). Accurate 
estimation of spawning frequency is 
important because the largest source 
of error in the estimation of SSB with 
DEPM is believed to be associated 
with spawning frequency (Stratouda- 
kis et al., 2006). 
Spawning frequency (S) is ex- 
pressed as the average number of 
spawnings per individual per day or 
as spawning interval (day) (in this 
study, the former definition is ad- 
opted). In both cases, it is estimated 
from the fraction ( F ) of mature fish 
that have a trait (spawning marker) 
related to imminent or recent spawn- 
ing, e.g., oocytes at migratory nucleus 
(MN) or hydrated (HD) stages indi- 
cating imminent spawning, and post- 
ovulatory follicles (POFs) indicating 
recent spawning (Hunter and Gold- 
berg, 1980; Hunter and Macewicz, 
1985). In the case of some clupeid fish 
populations, it is sufficient to have a 
rough estimate of the duration of a 
spawning marker, e.g., day-0 POF, 
day-1 POF, etc., because these popu- 
lations spawn synchronously during 
