International Journal of Aquaculture, 2013, Vol.3, No.19, 105
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(
population or stock) which are not reproductively
isolated from each other, may have limited
opportunity ange genetic material because o to exchf
geographic distance, barrier to migration or spawning
asynchrony. Low level of gene flow stocks may result,
over time, in their genetic divergence and species that
are subdivided into morphological and genetically
distinct stock are said to be structured. This
information will help to the development of selective
breeding programs applying quantitative genetic to
better the performance of domesticated shrimp stock
in aquaculture. Shrimp forming industry in south east
Asia, two fundamental problems have risen leading to
great economic loss, those are viral diseases, that
affect shrimp health resulting in large economic losses
in affected countries and effects of domestication on
genetic diversity levels in cultured lines. Genetic
diversity likely impacted during the domestication
process, besides, as result of culture stock they were
exposed to repeated bottlenecks as they were
developed in culture. This has led to an increasing in
consanguinity over time. Since the existence of natural
population subdivision may imply adaption to local
conditions, genetic assessment of the degree of population
structuring and gene flow among natural population are
practical ways of helping to preserve existing biodiversity
and maintaining valuable adaptive population.
The genetic diversity in the east coast appears to be
more than the west coast of India. This could be due to
a large fluctuation in the physic- chemical parameters
in the east coast because of several river drainage in
the east coast (Kumar et al., 2007).
M. dobsoni
populations from the west coast of India state Kerala
and Maharashtra clustered together, but Tamil Nadu
formed a separate group as east coast of India (Lakra
et al., 2010). Distribution of zoeae larvae of these
penaeid species are generally very coastal, as spawning
occur in 5 m-90 m depth, The life cycle of this species
can be completed in captivity, diminishing the
dependence on wild caught broodstock of these
species and allowing to commercially breed juveniles
to sustain production or to develop selective breeding
programs. Before attempting such commercial
operation, it is important to obtain data on genetic
diversity of wild stocks for successful broodstock and
genetic resources management since viable shrimp
hatcheries coexist in many of the shrimp farming
regions of the south east coast of Indian where
collection of larvae and breeding stocks from the wild.
It is susceptible to fluctuations in the availability of
wild resources as any capture fishery activity.
Therefore knowledge about genetic diversity and
population differentiation is imperative to assess
genetic variability in the wild population for proper
conservation. Monitoring of genetic variation with
molecular markers across generation is recommended
to reveal changes in variability that could be caused
by event such as genetic drift, bottleneck, inbreeding
or selection (Nahavadni et al., 2011).
DNA markers have allowed rapid progress in
aquaculture investigations of genetic variability and
inbreeding, parentage assignments, and species and
strain identification and in the construction of
high-resolution genetic linkage maps for aquaculture
species (Liu and Cordes, 2004). Nuclear DNA main
attractiveness is abundance in the genome, Mendalian
inheritances, and potential to detect high polymorphism.
The deleterious effects of inbreeding are to be avoided;
crossing organism from genetically different strains is
of critical importance. This can be done most
effectively if knowledge about genetic similarity or
differences between strains is available, especially
when pedigree information is lacking (Ferguson, 1994).
One criticism of mitochondrial DNA studies is that the
genes are linked and act as a single locus and nuclear
gene could serve as additional non linked genetic
marker of population genetic studies. These nuclear
markers would differ from mitochondrial marker in
their rates of evolution and biparental mode of
inheritance (France et al., 1999)
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; Mishra et al., 2009,
Lakra et al., 2010). It has been successfully employed
to determine genetic diversity in
P. vannamei
, (
Garcia
and Benzie, 1995), and
P.monodon
, (
Tassannakajon et
al., 1998) for population studies of penaeid species. In
Thailand found Banana prawns
F. merguiensis
and
F.
indicus
are clearly distinguished by RAPD marker
(
Phongdara et al., 1999). Due to variation in RAPD
profile and difficulties with reproducibility, however
many genetic researcher were made because RAPD-PCR
is a quick and reliable method for identifying genetic
diversity and similarity among various organism
(
Tassanakajon et al., 1997). Mishra et al. (2009)
recommended that RAPD technique is very