International Journal of Aquaculture, 2015, Vol.5, No.27 1
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7
between them (Supplementary Table 1 and Figure 5,
6). The
F
ST
and
Nm
values between TR-1 and TR-5
population (0.5917 and 0.3450) and that between
TR-1 and TR-4 population (0.5466 and 0.4147)
indicate that there is reduced gene flow from the
Mahananda (TR-2 and TR-5 population) and
Panchanoi (TR-4 population) rivers to the Fulbari
barrage (TR-1) population (Supplementary Table 1
and
Figure 5, 6). However in contrast, higher gene
flow is observed between Balason (TR-3 and TR-6)
and Fulabari barrage (TR-1) population (Supplementary
Table 1 and
Figure 5, 6). The differences observed in
the
F
ST
and
Nm
values between Mahananda,
Panchanoi and Balason river populations may be
attributable to several factors, viz, water flow pattern,
water volume, fishing extent and other possible
anthropogenic and/or geological activities. The
F
ST
value was lowest (0.2560) and gene flow (1.4534) was
highest between the Panchnoi River (TR-4) and
Champasari (TR-5) populations (Supplementary Table
1 and Figure 5, 6). Although these two regions are not
linked at the upstream region there is a possibility that
these two regions might be linked during the monsoon
season though flood plains causing mixing of
individuals between these two regions. This
intermixing of individuals as well as inter-breeding
may cause lower gene differentiation and high rate of
gene flow among these two sites (TR-4 and TR-5).
Moreover when we compared the six populations in a
pair-wise manner, we found that the TR-1 population
lies more divergent from other five populations and
gene flow was also lowered between TR-1 with other
five populations. The same was also true for TR-2
with other five populations. This confirms an
independent and gradual isolated genetic differentiation
across the population of
Badis badis
. The independent
genetic differentiation of this population may be
attributed to the geographical distance. The Nei’s
genetic distance and genetic similarity exposed a
distinct spatial relationship between the six
Badis
badis
populations. In the UPGMA based dendrogram
TR-1 population formed an outgroup which might be
due to the convergence of all other three river streams
along with the
Badis badis
gene pool to the barrage
before being released to Bangladesh. In general, this
spatial genetic architecture delineates the genetic
hierarchical structure of
Badis badis
populations
across the main river streams of the Terai region.
We have involved a population of five individuals
each from each collection site primarily because of the
dwindling population structure of the species.
However to compensate this weak point of the study
we have used a set (twenty-two) primers to generate a
robust data matrix. Our study revealed a distinct
pattern of genetic diversity and genetic divergence
that exists across the six
Badis badis
populations in
the study area. The populations were allopatrically
distant or separated from each other although gene
flow was still evident in the populations which may
prevent the population from inbreeding depression and
consequently maintaining their survival. Moreover, it
was also found with the help of
SHE
analysis,
F
ST
analysis and dendrogram of the six populations of
Badis badis
, that a genetic hierarchical structure was
present in the populations.
SHE
analysis was
employed to separate species diversity into its richness
and evenness components. The
SHE
analysis revealed
that the change in the genetic diversity of the
Badis
populations was due to altitudinal variation in the
genetic richness and evenness in the populations. We
have previously reported that the genetic diversity of
the
Badis badis
population in the major stream
(Mahananda and Balason river) of Terai region was
declining. Several anthropogenic interferences like
indiscriminate fishing, effluents from adjacent
households and factories, heavy use of fertilizers and
pesticides in the nearby tea gardens or excavation of
river beds along the banks for sand and gravel all may
be responsible for the decline of the overall diversity
of this threatened ornamental fish species in the Terai
region of West Bengal, India. Therefore, proper steps
should be taken to improve the environment to avoid
further losses. The genetic data obtained from the
present study lend support to the view that there is a
scope of stock improvement for this threatened
ornamental fish species.
3 Materials and Method
3.1
Survey and Sample Collection
An extensive survey has been carried out in different
spots of the major streams (i.e. Mahananda and
Balason river) of the Terai Region of West Bengal,
India. A total thirty fish (five individuals from each
collection spots) tissue samples of
Badis badis
were
collected from six different spots and geographic
co-ordinates were recorded with the help of GPS
(eTrex Vista HCx, Garmin, USA). We have previously
