International Journal of Aquaculture, 2013, Vol.3, No.13, 63
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performance of first feeding grouper, several issues
remain unsolved. For instance, water quality can be
easily deteriorated when the un-proper treated eggs
and trochophore are in used. Furthermore, how to
control the development speed of eggs and trochophore is
critical as once they are in the D shape sage, fish
larvae cannot digest it. Therefore careful feeding
management is important once this kind of live feeds
were introduced to the larvae rearing tank.
2.2.2
Rotifers
S-type and SS- type of
Brachionus
sp. are the major
rotifers used as live feeds for grouper larvae. As the
S-type rotifers (
Brachionus rotundiformis
)
are too
large for newly hatched grouper to ingest, SS-type
rotifers (
Brachionus
sp), or S-type rotifers screened to
<90 µm, are suitable for grouper larvae at first feed
(
Duray et al., 1997; Su et al., 1997; Watanabe et al., 1996).
Optimal prey density during the early larval stages is
10-20
organisms/mL (Ruangpanit et al., 1993; Tamaru
et al., 1995)
Rotifers as the major live feeds for marine fish larvae
normally contain low levels of polyunsaturated fatty
acid (PUFA) content (Conceição et al., 2010).
Evidences indicated that the lack of PUFA contents in
rotifers has leaded to fish slow growth, mass mortality,
mal-pigmentation, and deformity (Takeuchi et al., 1998;
Avella et al., 2007; Olivotto et al., 2006). Previous
study find that the eggs of grouper such as
E. coioides
contained high level of DHA, EPA, and ARA
suggesting their important in larval development
(
Alava et al., 2004). However, the content of EFA
such as eicosapentaenoic acid 20:5n-3 (EPA),
docosahexaenoic acid 22:6n-3 (DHA) and arachidonic
acid 20:4n-6 (ARA) in rotifers are relatively low when
compared to other live food (e.g., copepods) in nature
(
Sargent et al., 1999; Conceição et al., 2010).
Therefore, enrichment of rotifers with liquid
emulsions containing EFA is necessary to improve its
quality as fish food (Rainuzzo et al., 1997).
2.2.3
Copepods nauplii
In natural, copepods nauplii are the major food for
marine fish larvae. Due to the size advantage (smaller
than SS-strain rotifers) and superior nutritional value
to rotifers (McKinnon et al., 2003), copepods have
been widely used in larval grouper rearing in Asian.
The unique characters of copepods nauplii make it
becoming a more valuable live feed in the rearing of
grouper larvae. Apart from size advantage, copepods
contain higher essential fatty acids for fish larvae than
any other live feeds such as rotifers and
Artemia
nauplii (Evjemo et al., 2003; Støttrup and McEvoy, 2003).
Furthermore, the nutritional profiles of copepods
fulfill the nutrient requirement of fish larvae,
especially the content and ratio of PUFA, DHA, EPA,
and ARA (Venizelos and Benetti, 1999; Bell et al., 2003;
Nanton and Castell, 1998). Up to present, copepod
culture in intensive indoor and outdoor systems has
been successfully developed, however, due to the
technical constraints in rearing copepods, its mass
production at a commercial scale has not been
achieved (Stottrup, 2000; Hagiwara et al., 2001).
2.2.4
Artemia
nauplii
Artemia
is another common used live food following
the rotifers for larval grouper rearing. Nauplii instar I
and II are the most widely used forms of
Artemia
in
aquaculture. In China, adult
Artmia
was also used as a
food source for those fish not weaned to artificial diets.
Due to the lack of EPA and DHA, it is necessary to
enrich
Artemia
nauplii with oil emulsions before
feeding fish larvae (Ma et al., 2012). Oil emulsions are
general composed of fish oil and fatty acids ethyl
esters, providing essential fatty acids to fish larvae
in neutral lipid classes (Monroig et al., 2006).
Because of the character of inherent catabolism,
enriched nutritional components can also be absorbed
by
Artemia
nauplii after enrichment resulting in
great variation of nutrient contents (Naz, 2008;
Triantaphyllidis et al., 1995). Thus, timely harvesting
and storage of enriched
Artemia
,
and quick feeding to
fish are recommended to minimize nutrition loss after
enrichment (Ma et al., 2012).
3
Summary
The grouper aquaculture industry is expanding at a
fast rate, and there is great potential for this industry
to be further expanded. A number of key progresses
have been achieved in the past fews decades, and there
have been significant achievements in knowledge of
grouper rearing. Progress in grouper larval culture in
particular has been rapid over the past decade. In order
to improve the prodction efficiency, future resarech
should towards (1) the understanding of timing of live
food delevery to first-feeding grouper larvae, (2) the
nutritional requirments of first-feeding larvae and of