Yoneda et al.: Reproductive cycle, fecundity, and seasonal distributions of Lophius litulon 
369 
crease in HSI that is associated with increasing GSI is 
probably due to materials that have been stored in the liv- 
er becoming mobile and being transferred to the gonads. 
In teleosts, as in most other vertebrates, the precursor 
protein of yolk (vitellogenin) is synthesized in the liver. 
The secreted vitellogenin is selectively removed from the 
bloodstream by the developing oocytes (Wallace and Sel- 
man, 1981; Nagahama, 1987). The rapid accumulation of 
yolk probably accounts for the decrease in the weight of 
the liver. 
In many fish, batch fecundity is estimated by using mi- 
gratory nuclei or hydrated oocytes, which can be easily 
distinguished from the less advanced oocytes: e.g. Engrau- 
lis mordax (Hunter and Goldberg, 1980; Hunter et al., 
1985), Thunnus albacares (Schaefer, 1996), and Rhombop- 
lites aurorubens (Cuellar et al., 1996). We found that dur- 
ing and after the tertiary yolk stage, a large amount of ge- 
latinous material was rapidly secreted and accumulated 
in the ovarian lumen. Hence, counts of advanced oocytes 
from a small portion of the ovary, when extrapolated to 
the total weight of the gelatinous material, may give more 
variable estimates. These findings were also evident in L. 
setigerus (Yoneda et al., 1998a). However, the oocyte size- 
frequency profiles indicated that when the most advanced 
oocytes reached the secondary yolk stage, they formed a 
batch that was almost completely separated from the ad- 
jacent group of smaller oocytes. These ovarian character- 
istics of L. litulon imply that estimates of batch fecundity 
can be made only by using oocytes that have attained the 
secondary yolk stage. 
Both the immature and mature distribution of L. litu- 
lon ranged into the East China and Yellow seas, as pre- 
viously reported by Yamada (1986) and Tokimura. 1 This 
species is caught mainly at depths between 50 and 100 m 
and at temperatures ranging from 6 to 13°C (Yamada, 
1986; Tokimura 1 ). In the Yellow Sea, the Yellow Sea Cen- 
tral Cold Water, cooler than 10°C, is found throughout the 
year and there are few seasonal changes in water temper- 
ature (±2-3°C). The water of the East China Sea remains 
lower than 13°C owing to the influence of the Continental 
Coastal Cold Water in the winter and spring, whereas in 
summer it increases higher than 20°C (Kondo, 1985; To- 
kimura 1 ). These oceanographic conditions in the East Chi- 
na and Yellow seas may influence the migration of L. li- 
tulon from area to area throughout the year. A seasonal 
movement of L. litulon has also been reported in Sendai 
Bay (Kosaka, 1966; Omori, 1979). Lophius litulon are most 
abundant in shallow waters between February and June. 
From August through October, they disperse toward deep- 
er waters. This seasonal movement in Sendai Bay is ob- 
served mainly in immature fish and is thought to be as- 
sociated with their feeding activities (Kosaka, 1966). In 
L. arnericanus, a seasonal migration, thought to occur in 
response to changes in hydrographic conditions, has been 
observed along the northeastern coast of the United St ates 
(Jean, 1965; Almeida et al., 1995). 
During the February-May spawning season, mature 
males and females with ovaries in a condition that sug- 
gests they are either about to spawn, or have just spawned, 
are found in the East China Sea and the coastal waters off 
Kyushu. In contrast, immature individuals were distribut- 
ed throughout the East China and Yellow seas during this 
same period. This indicates that the spawning grounds of 
L. litulon cover a large area, extending from the East Chi- 
na Sea to inshore waters off Kyushu. Furthermore, our 
study reveals the migratory pattern of both sexes of L. li- 
tulon in relation to the spawning grounds in the period 
before the spawning season. In February, with the onset 
of the spawning season, females collected in the northern 
East China Sea had developing ovaries (secondary or ter- 
tiary yolk stage), whereas those collected in the Yellow Sea 
had immature or primary yolk stage ovaries. This finding 
implies that the start of the migration of females seems 
to be more dependent on ovarian development than ocean- 
ographic conditions. Different migratory patterns of the 
two sexes before spawning have also been reported in Eu- 
ropean plaice, Pleuronectes platessa, in the Straits of Do- 
ver off England (Arnold and Metcalfe, 1995). Our study 
has identified the spawning grounds and migratory pat- 
tern of L. litulon in broad terms. Further research is need- 
ed to identify specific spawning grounds and details of the 
migratory behavior of this species. 
Acknowledgments 
We are grateful to the officers and crew of the RV Kcuho 
Maru, Okinawa Prefecture, and the training ship Naga- 
saki Maru , Nagasaki University, for allowing us to board 
their vessels and to collect specimens, and to many fisher- 
men, especially members of the Yamada Suisan Company 
Ltd. and the Murayama Suisan Company Ltd., for helping 
us to obtain samples. We wish to express our gratitude to 
K. Kofuji for his report on spawning activity observed at 
Oarai Aquarium, and to R. G. Bakkala and B. N. Campbell 
for offering valuable suggestions and for critically reading 
this manuscript, and to anonymous reviewers for review- 
ing the manuscript and suggesting many improvements. 
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