International Journal of Aquaculture, 2013, Vol.3, No.19, 105
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as much as 100 km between the offshore inshore
habitats. Many marine species including the penaeid,
are thought to have a high dispersal capacity
throughout their geographic range during their larval
planktonic stage caused by oceanographic current, and
also the habitat of coastal species are rarely
continuous, heterogeneous genetic diversity could be
generated by some environmental factor like water
current and physical barrier and biological factors like
reproductive behavior (Feral, 2002). The gravid
P.
monodon
females spawn in the open sea. Benthic
postlarvae are found along the coast or in mangrove
swamps and other estuarine areas wild fry become
juveniles and adults in estuarine areas but return to the
sea for spawning. As for
F. indicus
,
the adult spawn
offshore, maintain till at post larval stage, The Post
larvae migrate using water current towards estuary
(
with estuarine juveniles) become juvenile which likes
mud or sandy mud at depths of 2 to 90 m. after mature
coming towards offshore. The coastal zone of and life
history of
P.semisulcatus
that adult spawn in off shore,
larvae migrate towards grass and algal bed near sea
shore become juvenile migrate to offshore to become
adult.
F.indicus
and
P.monodon
somewhat same
adapted life cycle rather than
P.semisulcatus.
These
attribute could be the reason why
P.semisulcatus
different geographical pattern of diversity against
P.monodon
and
F.indicus
.
In our study the genetic variation including all species
in the range of 6%~51%, this value close to the value
of
Metapenaeus dobsoni
genetic diversity 22.3% to
40.9% (
Mishra et al., 2009), and
Metapenaeus affinis
31.10%
~57.20% (Lakra et al., 2010) samples collected
form Indian coast. Zhuang et al. (2001a; 2001b) and
Song et al. (1999) reported that two wild kuruma
prawn populations from Taiwan Strait and Xiamen
water area had average heterozygosities of 0.214 and
0.245
respectively. In our study genetic diversity for
F. indicus
,
P. semisulcatus
and
P .monodon
0.275,
0.447
and 0.329 respectively.
Benzie (2000) reviewed penaeid prawns and concluded
that estimated variability from DNA-based markers
showed high level of diversity in natural population
than that inferred from allozyme. Random
amplification of polymorphic DNA is a simple and easy
molecular method to estimate genetic diversity in penaeid
shrimp, fish and shell fish (Zhuang et al., 2001a; 2001b;
Lakra et al., 2010). The results of
P. monodon
population differentiation are genetically significant
between Chumphon and Trat while using RAPD,
whereas these results did not show differentiation
between these samples while using mtDNA
polymorphism. From these findings, concluded that
under the presumption of selective neutrality of this
mitochondrial marker, biased female gene flow
between Trat and Chumphon
P. monodon
may exist
and be responsible for an anomalous differentiation
pattern (Klinbunga et al., 2001).
The studies on genetics indicated a very good
heritability of productive traits for penaeid shrimp,
and this could open a good outlook to detect related
genes for marker-assisted selections in future selective
breeding programs of shrimp (Hoa, 2009). One of the
domestication effects is the loss of rare alleles. The
changes in allelic diversity after bottlenecks may be
more striking than changes in heterozygosity
(
Allendorf and Ryman, 1987). A stick correlation
between loss in genetic variation and shrimp
production performance that would thereby reduce
their diversity, that is adaptive potential, relative to
their wild counter parts is well documented (Dumas
and Ramos, 1999; Sbordoni et al., 1986; Harris et al., 1990;
Xu et al., 2001; Zhuang et al., 2001a, 2001b). A
species that has little or no genetic diversity will
produce offspring that are susceptible to diseases and
have reduced biologic fitness and increased chances of
species extinction. In the present study, the penaeid
population have moderate to high genetic variation
and maximum three stock there, interbreeding among
these stocks which help to aquaculture industry which
prevail in these site to prevent the deleterious effect of
bottleneck. Therefore, in penaeid population, detection
of the genetic variation using different molecular
markers is useful to geneticists in genetic improvement
program of economically valuable species.
3
Materials and Methods
3.1
Collection of Samples
Fenneropenaeus indicus
(
H. Milne Edwards, 1837),
Penaeus monodon
(
Fabricius, 1798),
Penaeus semisulcatus
,
De Haan (1844) were collected from landing centre of
five district of East coast of Tamilnadu such Tuticorin,
Ramanthapuram, Puthukkottai, Nagapattinum, and
Chennai (Figure 7). In Tuticorin the
Penaeus
monodon
is not obtained. The collection period