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International Journal of Aquaculture, 2014, Vol.4, No.09 55
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at 96.8% for 2♂: 1♀ population (which is almost
similar to 1♂: 2♀ population at 96.2%) and the lowest
SI value was 93.7% for control population (almost
similar to 1♂: 1♀ at 94.1%). These results clearly
indicate the lower genetic diversity in terms of gene
diversity for the 1♂: 2♀ (H=0.06) and 2♂: 1♀
(H=0.05) populations. Gene diversity (H) of the
control and 1♂: 1♀ populations were 0.10 and 0.09
respectively which was almost similar and statistically
insignificant. However, the gene diversity values were
found to be statistically significant while 1♂: 1♀ and
control populations were compared with the 1♂: 2♀
and 2♂: 1♀ populations. Inter-population S
ij
showed a
very close genetic relation between 1♂: 1♀ vs. control
(94.7%) and 1♂: 2♀ vs. 2♂: 1♀ (95.6%) combinations.
But the S
ij
values for other combinations were
comparatively low and indicate less genetic similarity
between the population pairs. See et al., (2008)
obtained 50-80% inter-population genetic similarity
indices among 11 different populations of giant
freshwater prawn. In the present study, S
ij
values were
far higher because all the broods used were collected
from the same river and then they were stocked at
different sex ratios.
Statistically significant F
ST
values were obtained for
the 1♂: 1♀ vs. 1♂: 2♀, 1♂: 1♀ vs. 2♂: 1♀, 1♂: 2♀
vs. control and 2♂: 1♀ vs. control combinations but
statistically insignificant values were obtained for the
1♂: 1♀ vs. control and 1♂: 2♀ vs. 2♂: 1♀ population
pairs; this clearly indicates the negligible genetic
variation between the later two combinations. Khan et
al. (2014) reported that the F
ST
values between the
population-pairs ranged from 0.012 to 0.021 of three
riverine population of
M. rosenbergii
in Bangladesh.
This level of genetic differentiation between the pairs
of populations is considered as low (Balloux and
Lugon-Moulin, 2002). The lowest value of F
ST
(0.012)
between the Paira and the Pashur population indicated
relatively closer relation between these rivers over the
Naaf population.
This could be ascribed as to the selection for a single
potential mate in nature and which is similar to the sex
ratio 1♂: 1♀. In case of 2♂: 1♀ combination, number
of male is increased in the population that lead to the
occurrence of male competition as it is evident that
male territory formation is common in
Macrobrachium
rosenbergii
. Due to this problem, all the males were
not able to take part in copulation with females and
only larger dominating blue clawed males copulated
with female, thereby providing reduced genetic
variability for this sex ratio. The pair wise genetic
distance (Nei’s genetic distance, D) values revealed
the highest value at 0.012 for both the 1♂: 1♀ vs. 2♂:
1♀ and 2♂: 1♀ vs. control combinations, and the
lowest value (0.007) for 1♂: 1♀ vs. control
combination. All of the results clearly demonstrate the
very lower genetic variability (very closer genetic
relation) between 1♂: 1♀ vs. control combination. See
et al., (2008) observed the highest genetic distance
value as 0.0653 between two populations and the
lowest genetic distance value as 0.03 in case of 11
different populations of giant fresh water prawn in
Malaysia. Khan et al. (2014) observed and expected
heterozygosities were found to be 0.574 to 0.634 and
0.804 to 0.827, respectively are in agreement with the
range reported by other authors (Chareontawee et al.,
2007; Schneider et al., 2012).
Figure 6 represents the UPGMA dendrogram for the
larvae produced from broods stocked under different
sex ratios together with larvae produced from natural
broods. The UPGMA dendrogram based on Nei’s
(1973) genetic distance indicated the segregation of
four different experimental groups/populations of
prawn into two clusters: 1♂: 1♀ and control
populations in one cluster whereas 2♂: 1♀ and 1♂:
2♀ in another cluster. Results of this study clearly
indicate the suitability of maintaining 1♂: 1♀ sex
ratio in brood banks of giant fresh water prawn in
order to produce genetically variable and high
yielding post larvae from the hatcheries. Results of the
present experiment further indicated that there is a
clear role of sex ratio on the genetic variability of
larvae of giant fresh water prawn and thus
maintenance of appropriate sex ratio is a vital issue for
brood stock development for this species.
4 Conclusion
In the present study, genetic variability was assessed
successfully for the giant freshwater prawn post larvae
produced from 3 different sex ratios and post larvae
produced from the natural broods. Results obtained
from this study clearly support for the maintenance of
1♂:1♀ sex ratio for brood stock development.
Collection of
Macrobrachium rosenbergii
broods for
hatcheries from nature has already created a sharp