Basic HTML Version
International Journal of Marine Science 2013, Vol.3, No.40, 319-332
http://ijms.sophiapublisher.com
327
routine analyses using minimal cost-effective
resources at the field laboratory. As in this study,
farmers would attain a high quality shrimp yield at the
end of the culture period. Moreover, the release of
water from the culture ponds at the end of the culture
would not alter the balance of autochthonous
micro-flora in the adjacent water bodies. Future
studies would be directed towards increasing the
stocking density by introducing aerators without
compromising the environmental quality. However,
this has to be carried out in a step-wise manner to
understand the grid of interactions in detail as it would
help us scale the yield gradually.
3 Materials and methods
3.1 Culture ponds, farm management and approach
Two identical shrimp culture ponds (P1 and P2; Figure
2) in Kumta taluka of Karnataka state, west coast of
India (14.42
°
N and 74.40
°
E) were chosen as part of
the Indo-Norwegian co-operation project entitled
“Environmental management Strategy for Coastal
Aquaculture Practices in South-western Coastal India”.
Kumta experiences very hot summer with temperature
varying between 28-36
℃
. The impact of winter is
less with temperature ranging from 20-26
℃
. Rainfall
in the region is seasonal (June to September), but
heavy with annual precipitation exceeding 4000 mm.
The shrimp farm had an easy access from national
highway no. 17 and a good power supply. The site was
also equipped with a field laboratory to carry out
physical, chemical and biological analysis of pond
water and sediment. The culture ponds had a water
Figure 2 Layout of the shrimp farm (not to scale) near Alvekodi
village in Karnataka state, west coast of India. Sampling points
in the ponds have been denoted as A, B and C
spread area of ~ 0.60 ha and an average depth of 1.2 m.
The source of water to the culture ponds was an
adjacent tidal fed creek which was located about 3 km
away from the sea.
Pond management practices as applicable to modified
extensive culture method were followed. Before
stocking, the ponds were sun dried for a period of one
month and lime was applied to the bottom of the pond.
The ponds were filled with water five days prior to
stocking during high tide with the help of sluice gates
and electric pump. White spot syndrome virus (WSSV)
negative post-larvae (PL) of tiger shrimp
P. monodon
as confirmed by the polymerase chain reaction test
were procured from a local hatchery. Larvae were
actively moving around with no visible signs of
disease or morbidity and were transferred into the two
production ponds at a stocking density of 5 PL m
-2
.
No water exchange was done for the first 30- day of
culture (doc). Due to the close physical proximity, the
climatic conditions in both the ponds were almost
similar. No artificial aeration was used during the
culture period. An additional dose of lime was applied
regularly after 40 days of culture (doc) to adjust the
sediment pH around 7.0. Shrimps were fed with
commercial shrimp pellets procured from C P
Aquaculture (India) Pvt. Ltd. at 10% of their body
weight twice a day during the juvenile stage.
Precautions were taken to adjust the feeding according
to the biomass and survival. Towards the end of the
culture period, high organic load and nutrients in aqua
farms can lead to eutrophic conditions. Further,
oxygen-depletion and production of sulfide in
sediments and water column can stress free-swimming
fish (Bagarinao and Lantin-Olaguer, 1998). Therefore,
the feeding rate was gradually reduced to 2% to prevent
accumulation of organic matter within the ponds.
The ponds were monitored for one shrimp harvest
cycle covering 135 days to assess the variation in
physico-chemical parameters along with the
abundance and diversity of culturable vibrios.
3.2 Collection of samples
Samples of source/creek water and pond water were
collected one day prior to transfer of post-larvae and
thereafter at fortnightly intervals after stocking from
0-doc until 135-doc between September 2003 and
January 2004 at three pre-determined sampling