International Journal of Aquaculture, 2013, Vol.3, No.12, 55
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62
http://ija.sophiapublisher.com
59
predominant factor affecting the growth of fish in
early life stage (Yin 1995). In species such as
yellowtail kingfish (
Seriola lalandi
),
growth is
normally found accelerated after the digestive system
is fully functional (Ma, unpublished data). In the
present study, bluefin leatherjacket grew slowly in the
original developmental stage (0 dph~16 dph), the
specific growth rate was only about 4.7%/day. The
growth turning point was found around 20 dph, when
the growth was accelerated. This may indicate that a
more efficient digestive system was formed around
this stage.
In present study, two heavy mortality periods were
observed, which were found between 5 dph~10 dph
and 30 dph~60 dph. During the first mortality period
(5
dph~10 dph), nearly 80% of fish were lost. Within
this period, dead fish were examined under stereo
microscope. Dead fish was showing nutrition defeated
sign that the body of fish was dark, and emaciated.
Although feeds can be found in fish gut, little of them
were digested. We suspected that this may cause by
the D shaped larvae of Pacific oyster as the chitin shell
of D shaped larvae cannot be digested by fish larvae,
and its unique character may also block the digestive
tract of fish larvae. Therefore, in the rest of our
production run we started to control the development
stage of the Pacific oyster larvae to make sure less D
shaped larvae were presented in the rearing tanks and
a protocol has also been developed (Guan et al. 2012).
The second mortality period was started from 30 dph,
which occurred after weaning started. Previous study
have indicated that mortality happened within this
period was contributed by cannibalism (Hoey and
McCormick 2004), feeding decrease or suspend
(
Folkvord and Otterib 1993), stress response enhancement
(
Wedemeyer 1972), disease and so on. In the present
study, cannibalism began from 30 dph, chasing, biting,
and chocked fish can be easily found in each rearing
tanks. In order to reduce cannibalism, in the rest of our
production run we started to grade the fish weekly,
and increased the water exchange rate during the day
time which the cannibalism was reduced.
In summary, the present study demonstrated that
bluefin leatherjacket was feasible breeding under
artificial environment. Aspects regarding to bluefin
leatherjacket breeding have been successfully explored.
Although the final seeding rate was low, as the first
breeding experiment under commercial scales, our
results can still provide the fundamental information
on artificial breeding on this species. Future study
should towards increasing the hatching rate and
understand the digestive physiology of bluefin
leatherjacket.
2
Materials and Methods
2.1
Broodstocks Management
Broodstocks (395 fish, mean total length=(277.8±30.0) mm)
were caught in Bohai Sea, P.R. China, and have been
acclimated in the artificial environment for 15 months
in a commercial hatchery (Yantai, Shandong Province,
P.R. China). A total of 216 fish was used in this study.
The fish were kept in the indoor cement tank
(
diameter 7.0 m; water depth 0.8 m~1.0 m) and the
culture density was maintained at 4 fish/m
3
.
Ambient
seawater filtered by 100 µm filter was supplied to the
rearing tank at 10 m
3
/
h. Salinity was maintained at
30‰
through this study. A nature photoperiod was
used in this study. The photoperiod at the start of the
spawning season (June) was 13 h light: 11 h dark, and
increased to a maximum day length in August (14 h
light: 10 h dark) at the end of spawning season (at the
end of August). Vigorous aeration was provided
through diffuser stones. Fish were hand-fed
once per
day to the level of satiation in the morning, with
approximately (7~10)% amounts (by weight) of mixture
diet (30% white-hair rough shrimp (
Trachypenaeus
curvirostris
,
Stimpson), 40% pacific oyster (
Crassostrea
gigas
),
15%
Mytilus edulis
and 15% squid (
Loligo
sp.
).
Pre to the spawning season, broodstocks (32 fish
per tank) were transferred from the culture tank to
spawning tanks (concrete, 28.8 m
3
)
with a sex ratio of
1:1 (
female: male). Natural spawning occurred when
the ambient water temperature increased from 19
℃
to
21
℃
in the spawning seasons.
2.2
Eggs Collection
The collection of eggs for larvi-culture started from
early June to the end of July. The collection was
stopped when egg quantity and quality decreased
to a degree that made larvi-culture unviable for
commercial proposes. The adhesive eggs from natural
spawning were collected by using plastic corrugated
plates (50 cm×50 cm) which were placed on the
bottom of each spawning tank. These plates were
placed at 10:00 am before each spawning event, and
removed in the following day. Eggs were transferred to