NOTE Munehara: Reproductive biology and early life stages of Podothecus sachi 
617 
had 13, 16, and 15 rays in its dorsal, anal, and pecto- 
ral fins, respectively. On the 42nd day, a specimen 
measuring 8.7 mm SL had 10 spines and 13 rays on 
its dorsal fin and 15 and 16 rays on its anal and pec- 
toral fins, respectively, forming a full complement 
(Fig. 4H). The pelvic fins were still buds. The open- 
ing position of the anal and the genital pore began 
moving from just anterior to the anal fin toward the 
base of the pelvic fins. Whiskers, a mustache, and 
pelvic fins first appeared in a 15.6-mm-SL specimen 
on the 60th day (Fig. 41) and were completely formed 
in a 24.6-mm-SL specimen on the 93rd day. Juvenile 
P. sachi almost corresponded to adults in morphologi- 
cal features, but movement of the anal and genital pore 
openings were only half finished. The 24.6-mm speci- 
men swam, using its elongated pectoral fins, but 
never used its posterior trunk for propulsion owing 
to hardened bony plates. 
Discussion 
Internal gametic association and external 
fertilization 
As noted, P. sachi eggs placed in seawater and with- 
out artificial insemination began to develop and grow 
to juveniles, whereas eggs maintained in ovarian 
fluid showed no signs of development. In addition, 
histological observations of eggs directly obtained 
from the ovary showed that spermatozoa had entered 
the micropyle before contact with seawater, indicat- 
ing that fertilization was not initiated in the ova- 
rian fluid. This observation demonstrates that the 
spawning mode of P. sachi is of the internal gametic 
association type, reported in previous studies of copu- 
lating cottids (Munehara et al., 1989, 1991, 1994a; 
Koya et al., 1993). Atlantic wolffish, Anarichas lu- 
pus (Perciformes, Anarhichadidae), is also known to 
undergo copulation before egg laying, but the spawn- 
ing mode of this fish is not comparable to that of P 
sachi because inseminated eggs of Atlantic wolffish 
develop internally (Pavlov, 1994). This information 
seems to support Yabe’s hypothesis (1985), based on 
comparative osteological and myological observa- 
tions, that the family Agonidae may be the most 
closely related family to the Cottidae. 
Early life history 
Many larvae and juveniles, 8.3-25.1 mm SL, have 
been collected by plankton nets (Maeda and Amaoka, 
1988). In the present study, the largest specimen took 
93 days to grow to 24.6 mm SL after hatching. Thus, 
P. sachi probably inhabits the pelagic ocean during 
its first three months. It seems reasonable that whis- 
kers and mustache, which function as sensory or- 
gans for detection of benthic prey (Sato, 1977), are 
completed before juveniles become benthic. 
Reproductive style of agonid species 
Information on the reproduction of agonids is avail- 
able for only 6 of 50 species (Table 2). Many common 
characteristics are recognized among these species. 
First, the reproductive behavior of the Agonidae 
involves copulation. All the agonid species whose re- 
productive styles are known ( Agonomalus probo- 
scidalis, Occella iburia, and Bracdyopsis rostratus) 
have been described as internally fertilizing species 
on the basis of the development of eggs deposited 
without male involvement (Iioka and Gunji, 1979; 
Sugimoto, 1987; Aoyama and Onodera, 1989). These 
agonids probably exhibit external fertilization with 
internal insemination, as does P. sachi, because B. 
rostratus has been determined to be of the internal 
gametic association type from the same investiga- 
tions done for P. sachi, and information on internal 
fertilization of the agonids was proposed prior to the 
first recognition of the internal gametic association 
in teleost fishes (Munehara et al., 1989). 
A second characteristic of the reproductive style is 
that agonids have a long embryonic period, ranging 
from 100 days to 1 year. In addition to the Agonidae, 
such extraordinarily long embryonic periods in te- 
leost fishes are known for only a few trichodontids 
and cottid species (Okiyama, 1990; Munehara and 
Shimazaki, 1991). 
The third and fourth characteristics are egg depo- 
sition in concealed sites and lack of parental care. 
Naturally deposited egg masses of Agonus cata- 
phractus were collected from the roots of kelp ( Breder 
and Rosen, 1966). Spawning of captive Agonomalus 
mozinoi and A. proboscidalis was performed by con- 
cealing eggs in the exoskeletons of invertebrates or 
between rocks (Marliave, 1978; Aoyama and 
Onodera, 1989). Egg masses of B. rostratus were 
found deposited on the bottom of a tank, but the 
spawner was kept in a bare tank with no suitable 
substrate (Sugimoto, 1987). It is still unknown where 
P. sachi spawns its eggs. However, it is probable that 
the spawning of this fish involves brood hiding and 
lack of parental care because this species has a re- 
tractable genital duct and a long incubating period, 
similar to other copulating cottids that deposit their 
eggs into sponges, polychaete tube colonies, and nar- 
row fissures (Gomelyuk and Markevich, 1986; 
Munehara, 1991, 1992, 1996). Deposition of egg 
masses on such spawning substrates limits preda- 
tion on the eggs. In addition, flagellar movements of 
