International Journal of Aquaculture, 2013, Vol.3, No.13, 63
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Figure 1 Embryonic development of
Epinephelus malabaricus
Note: A: Two-celled stage; B: Four-celled stage; C: Eight-celled stage; D: 16-celled stage; E: morhula stage; F: gastrula stage; G:
appearance of embryonic shield; H: closure of blastopore; I: appearance of optic vesicles and mytomes; J: 18-myomere stage; K:
beginning of motility; L: before hatching (Leu et al., 2005)
for the normal development of embryos (Ma et al., 2012).
Evidence indicate that the percentage of normal eggs
increases with the increase of
n
-3
highly unsaturated
fatty acids (HUFA) in broodstocks diets of gilthead
seabream (
Sparus aurata
) (
Fernández-Palacios et al., 1995).
Therefore, proper control of broodstocks nutrition can
improve egg quality and enhance survivorship in
marine fish larvae (Izquierdo et al., 2001).
1.1.2
Temperature
Temperature can also affect embryonic development
of grouper larvae. Watanabe et al. (1995) found that
the variations in water temperatures within an
ecological range can markedly influence development
rates and survival of pre-feeding Nassau grouper
(
Epinephelus striatus
)
larvae. Table 1 shows the eggs
diameter, incubation temperature, hatching time in 10
grouper species. Clearly, during the grouper embryonic
development, with the increased incubation temperature,
the hatching time was decreased. Similarly, studies in
other species have been demonstrated that higher
temperature accelerates development rate (Bermudes
and Ritar, 1999; Das et al., 2006; Moran et al., 2007;
Kazuyuki et al., 1988; Miranda et al., 1990). For
instance, the development rate of mackerel (
Scomber
scombrus
)
eggs at 17.8
℃
is almost three times
faster than at 8.6
℃
(
Figure 2, Figure 3). A similar
result has also been reported in striped trumpeter
(
Latris lineata
)
when compared with incubation
temperatures between 16.2
℃
and 8.1
℃
(
Bermudes
and Ritar, 1999). However, high temperature over a
tolerable range may lead to heat shock and fish
mortality (Hopkins and Dean, 1975; Kiyono and
Shinshima, 1983).
Figure 2 Functional relationship between developmental time,
temperature and embryonic stage of mackerel eggs
Figure 3 Fitted relationship between developmental time and
temperature at each embryonic stage (Mendiola et al., 2006)
Not like other species, grouper eggs and newly
hatched larvae (such as
Plectropomus leopardus
)
are
very sensitive to stress and handling (personal
conmunication with Mr Zhang, Xincun, Hainan
Province, P.R. China 2013). Therfore, to minimize the