International Journal of Aquaculture, 2013, Vol.3, No.13, 63
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fasciatus
and
E. suillus
are relative long (30-35 days)
(
Lim, 1993; Duray et al., 1997; Kawabe and Kohno, 2009).
The cause of this kind long feeding period in grouper
larvae may relate to the small size of body and narrow
mouth gap at hatching (Table 1). In order to improve
survival rates during the first feeding period, some
small zooplanktons such as copepod nauplii, egg and
trochophore of bivalve have also fed to larval grouper
along with rotifers (Marte, 2003; Lim, 1993).
Figure 5 Body length, diet, and water temperature during the
rearing of
Epinephelus fasciatus
.
Vertical lines indicate mean ±
SD (Kawabe and Kohno, 2009)
2.2
Live Feeds
The production of live feeds with small size
characteristics is an important hatchery operation in
grouper breeding (Lim, 1993). Since groupers have
extremely small mouth gap, under some particular
situation, rotifer may not fulfill the size of requirement
for the first feeding grouper larvae. Therefore, lots of
efforts have been to find the suitable first feeding feeds
for grouper live (Russo et al., 2009; Doi et al., 1997;
Reyes et al., 2011).
2.2.1
Eggs and trochophore of bivalve
Eggs and trochophore of bivalves such as mussels and
oyster have been widely used as first feeding live
foods for grouper larvae in the past because of the size
advantage. For instance the, size of eggs and trochophore of
green mussel
Perna viridis
are 55-60 µm and 60-80 µm
respectively (Lim, 1993), while the egg size of Pacific
oyster is about 45-62 µm (Pauley et al., 1988). The
most efficient way to spawns oyster and mussels is
temperature manipulation induction. In our recent
study, eggs and larvae of
Pinctada martensi
were used
to feed the newly hatched
Plectropomus leopardus
larvae, on 5 day post hatching, the feeding rate
reached to 45% (unpublished data).
The spawning of mussels is normally induced through
physical, chemical, or biological methods. Because of
the efficiency and easy operation, “Temperature
shock” is one of the most frequently used physical
methods in inducing spawns of green mussels. When
applied “temperature shock”, the mussels were
immersed in warm seawater which the water
temperature was 4-5
℃
higher than the rearing
temperature, then followed by cold seawater treatment
which the water temperature was 4-5
℃
lower than
the rearing temperature. Upon complete the induction,
the mussels were placed into spawning tank
(50
L~150L), and the spawning activity normally
occurred within 1 h. In order to minimize pollution of
seawater caused by deterioration of the milt, male
mussels were removed immediately after milt
production (Lim, 1993). Fertilized eggs were demersal
eggs which can be collected by siphoning the bottom
of the tank. After collection, eggs were washed via 20
µm screen to eliminate as much as milt before feeding
to the larval grouper.
Similar to the method used in mussels, pacific oyster
can also be induced by temperature cycling.
Temperature cycling method involves placing sexually
matured oysters in water at a certain temperature then
slowly increasing the temperature over a period of
time. For instance, when applied this method to
induce oyster, the oysters were exposed to 20
℃
,
then
every 5 minutes increased 1
℃
until the water
temperature reached to 28
℃
(
PIRSA,
http://www
.
pir.sa.gov.au/aquaculture/aquaculture_industry/oyst
ers). Apart from temperature induction, eggs and milt
can also be obtained directly from sexually matured
oysters by dissecting the gonads. Currently,
commercial production of trochophore oyster is also
available in the market, for example “TrochoFeed”
which is actually frozen oyster trochophore-stage
Pacific oyster. The products are preserved in liquid
nitrogen and can be used directly after thrown.
In practice, grouper larvae are normally feed on eggs
and trochophore-stage bivalve for two days during the
first feeding period (Rimmer, 2000). A feeding study
indicates that a combination of oyster trochophore and
small rotifers (either SS-strain, sieved S-strain, or
neonates) is the best initial feed (Su et al., 1997; Doi
et al., 1997). Although evidence indicates that the
combination feeding protocol can improve the larval