International Journal of Aquaculture, 2013, Vol.3, No.13, 63
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67
reach PNR, thus fish at 25
℃
and 27
℃
had less
time to establish their feeding capability than at 21
℃
and 23
℃
.
This may explain why massive mortality
occurred earlier at high temperature than at low
temperature. In grouper larvae such Malabar grouper
(
E. malabaricus
)
are very vulnerable to starvation, the
feeding windows for
E. malabaricus
cultured at 28
℃
are only 24 h after mouth opening (Yoseda et al., 2006). In
order to increase survival and reduce starvation, it is
necessary to reduce the culture temperature within the
first feeding stage as evidence from previous
studies indicate that lower temperature can delay
exhaustion of yolk reserve and starvation in other
species (Dou et al., 2005; Blaxter and Hempel, 1963b;
Yin and Blaxter, 1987). After compared the hatching
success and survival rate in a previous study,
Watanabe et al. (1995) suggest that a lower temperature
may be advantageous to higher temperature for
incubating eggs and for rearing first feeding
E.
striatus
when prey concentrations are limiting.
Similarly, an operating protocol has been proposed by
Ma et al. (unpublished) that use low temperature at the
initial feeding stage to improve survival and increased
temperature to promote feeding and growth in later
stage in yellowtail kingfish larvae culture.
1.2.2
Light intensity and tank color
Light intensity and tank color in the rearing tank may
affect the successful grouper larvae feeding as most of
marine fish larvae are visual feeders, and light plays
an important role in the foraging behavior of fish
larvae (Monk et al., 2008). Previous study in
E. suillus
indicate that no significant preference between black
and tan color regarding to the food intake and growth
(
Duray et al., 1996). However, more and more
evidence indicates that tank color preference is more
species dependent. For example research in species
such as herring and turbot indicate that black wall
tanks give a good contrast between food and
background (Blaxter, 1968; Howell, 1979), while
haddock (
Melanogrammus aeglefinus
)
larvae did not
grow and survive well in the tank coated with black
wall with low light intensity (Downing and Litvak, 1999).
More recent study in juvenile barramundi (
Lates
calcarifer
)
indicate that color preference changed as
an effect of the ambient light environment (Ullmann et
al., 2011). Therefore research should looking into both
factor may improve the feeding rate of fish larvae.
Surprisingly, little information can be found in
literature regarding to grouper larvae preference.
Therefore, future research should also towards to obtain
the optimal tank color and ambient light environment.
1.2.3
Water surface death
In the larval culture of several marine teleosts, large
numbers of dead larvae are often observed on the
water surface around the time of first feeding (Kaji et
al., 2004). The cause of surface death has been
considered as a consequence of being trapped on the
water surface by the water surface tension when
body surface is exposed to the air (Kawabe and
Kimura, 2007; 2008). Surface death is a heavy
mortality factor in yolk-sac grouper larvae such as
E.
akaara
(
Kaji et al., 1995; Yamaoka et al., 2000),
E.
septemfasciatus
(
Tsuchihashi et al., 2003),
E. bruneus
(
Sawada et al., 1999),
E. fasciatus
(
Kawabe and
Kohno, 2009). In order to overcome this problem, the
addition of an oil film on the water surface is normally
used to reduce water surface tension and prevent the
occurrence of mass surface deaths of fish larvae
(
Yamaoka et al., 2000; Kawabe and Kohno, 2009).
However, evidence indicates that the outcome of using
oil film to prevent surface death varied among
hatchery and the removal of oil film from rearing tank
was difficult (Yamaoka, 2001). As an alternative
substitute, egg white has been used to prevent surface
death (Kaji et al., 2003).
2
Feeding Protocol and Live Feeds
2.1
Feeding Protocol
At hatching, the size and mouth are very small in
groupers such as
E. coiodes
,
E. malabricus
,
E.
fuscoguttatus, E. suillus
and
C. altivelis
(
Table 1). The
mouth gape at first feeding of
E. suillus
was about
150-180
µm (Maneewong et al., 1986), and was about
250-300
µm in
E. marginatus
(
Glamuzina et al., 1998).
As the prey selection criteria are more by size than by
taste or other senses (Yufera and Darias, 2007;
Fernandez-Diaz et al., 1994; Planas and Cunha, 1999),
the small mouth gape in early grouper larvae period
limits the choice of initial live food to minute
zooplankton such as copepod nauplii (Marte, 2003),
eggs and trochophore larvae of mussel or oyster (Lim, 1993;
Doi et al., 1991). Figure 5 shows a feeding
management plan for
Epinephelus fasciatus
.
Not like
feeding protocol used in other marine fish larvae, the
rotifer and
Aretmia
nauplii feeding periods in the
grouper species such as
E. tauvia
,
E. fuscoguttatus
,
E.