612 
The reproductive biology and 
early life stages of Podothecus sachi 
(Pisces: Agonidae) * 
Hiroyuki IVSur&ehara 
Usujiri Fisheries Laboratory, Faculty of Fisheries, Hokkaido University 
Minamikayabe-cho Usujiri 152, Hokkaido, 041-16, Japan 
E-mail address: hm@fl hines.hokudai.ac.jp 
Within the agonids, 20 genera and 
50 species are recognized, with 
most distributed from the bottom 
of the north Pacific Ocean to the 
Bering Sea (Nelson, 1984). The 
agonid body is covered with bony 
plates and is unusual among teleost 
fishes. Several taxonomic studies 
have been conducted (Jordan and 
Evermann, 1898; Matsubara, 1955; 
Kanayama, 1991); however, little 
ecological information on the agonids 
exists because of their poor com- 
mercial value and small population 
density. Even for the sail-fin poacher, 
Podothecus sachi, the most common 
of the Japanese agonids, only larvae 
and juveniles have been reported 
from the adjacent waters of north- 
ern Japan (Maeda and Amaoka, 
1988). Past reports concerning the 
reproductive ecology of agonids 
have suggested that they have in- 
ternal fertilization and that fe- 
males produce small clutches of 
eggs almost daily (lioka and Gunji, 
1979; Sugimoto, 1987; Aoyama and 
Onodera, 1989). Recently, eggs of co- 
pulating cottids that were thought 
to undergo internal fertilization 
were shown to be fertilized by the 
received spermatozoa only after 
eggs were deposited (Munehara et 
al., 1989, 1991, 1994a, in press; 
Koya et al., 1993), i.e. there is an 
internal deposition of sperm that do 
not penetrate the ova or egg until 
after the latter are spawned and 
free in the environment. This 
spawning mode, named the inter- 
nal gametic association (Munehara 
et al., 1989), is characterized by the 
deposition of unfertilized eggs 
whose paternity has been fixed be- 
fore spawning (Munehara et al., 
1990; 1994b). This spawning mode 
is so unique that it is not included 
in other categories of the parity 
mode of fishes, as determined on an 
evolutionary basis (Wourms et al., 
1988). A comparative osteological 
and myological study on Scor- 
paeniformes indicated that the 
Agonidae family is most closely re- 
lated to the Cottidae family (Yabe, 
1985). Therefore, it is possible that 
the internal gametic association 
mode of spawning that occurs in 
agonid fishes may provide informa- 
tion concerning the relation of the 
two families. In this study, I report 
on the reproductive biology and the 
early life stages of P. sachi, compar- 
ing them with those of other agonid 
fishes. 
Materials and methods 
Three adult females of P. sachi were 
collected with gill nets from off- 
shore bottom waters (60-80 m 
depth) at Usujiri, southern Hok- 
kaido, 7 October 1992. After the live 
fish had been transported to the 
laboratory, their ovaries were sur- 
gically removed, and ripe eggs and 
ovarian fluid were extracted. Great 
care was taken to prevent contami- 
nation by seawater, urine, and 
blood. The ovarian fluid was iso- 
lated with a pipette for use in the 
following test. To determine if egg 
development began before or after 
contact with seawater, eggs of each 
female were placed in separate 
petri dishes containing either ova- 
rian fluid or seawater at 6°C. After 
20 hours, the number of develop- 
ing eggs were counted on the basis 
of occurrence of cleavage and for- 
mation of the blastodisc, which 
were regarded as signs of initial 
fertilization and autoactivation, 
respectively. 
Histological observations were 
carried out on several eggs before 
exposure to seawater to determine 
if internal fertilization occurred. 
Ovaries were examined to decide 
their developing mode. The ovaries 
were fixed in Bouin’s fluid. Serial 
paraffin sections, 5-8 |im, were pre- 
pared and stained with Delafield’s 
hematoxylin and eosin. The crite- 
ria of the maturing oocytes followed 
the classification of Yamamoto 
(1956). 
Eggs remaining from the above 
observations were used for morpho- 
logical observation of the early life 
stages of this fish. The eggs not 
used for artificial insemination 
were kept in a 1-L glass dish at a 
mean water temperature of 5°C. No 
bubbling stone was placed in the 
dish, but half of the seawater was 
replaced once a week. Juveniles 
were fed nauplii of Artemia salina. 
Measurement and observation of 
embryonic development were con- 
ducted once every 1-3 days. Sam- 
pling of hatched fish was done at 
intervals of 1-2 weeks until 93 days 
after hatching. Specimens were 
observed under a microscope after 
fixation in 5% neutral formalde- 
hyde solution. Terminology of the 
* Contribution 117 from Usujiri Fisheries 
Laboratory, Faculty of Fisheries, Hok- 
kaido University, Hokkaido, Japan. 
Manuscript accepted 19 March 1997. 
Fishery Bulletin 95:612-619 (1997). 
