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Standardising stocking density for freshwater prawn Macrobrachium rosenbergii (De Man, 1879) farming in coconut garden channels

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The effect of stocking density on the population structure, growth characteristics and production of freshwater prawn Macrobrachium rosenbergii in coconut garden channels was studied. A randomised block design of four treatments andfour replicates was used and the only difference being the stocking densities which ranged from 5000ha-1 to 25,000ha-1. The mean weight and survival at the time of harvest varied from 55.5 g to 101.7 g and 28.21% to 69.44% respectively. At lower densities the proportion of undersized non-marketable prawns was relatively low. However, net production increased with stocking density from 90.1 (TC-1) to 199.7 kg. ha-1. 8 months-1 (TC-4). Final marketable yield structure and economics revealed that the stocking density of 15,000ha-1 was optimum for coconut garden channels in Kuttanad. Present study suggests that the profit incurred from freshwater prawnfarming is directly related with production of larger orange-clawed and blue-clawed morphotypes. Hence stocking density was found as an essential component for ensuring better marketable yield and improving the economic returns. This study provides significant information since most coconut garden channels are abandoned water areas which when utilised properly can be an additional source of income especially to agriculture farmers in India and other Asian countries.
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Asian Fisheries Science 24 (2011):354-366
Asian Fisheries Society
ISSN 0116-6514
Standardising stocking density for freshwater prawn
Macrobrachium rosenbergii (De Man, 1879) farming in
coconut garden channels
K. RANJEET1* and B. MADHUSOODANA KURUP2
1PG Department & Research Centre in Aquaculture and Fishery Microbiology, MES Ponnani College
Ponnani South P.O., Malappuram (Dist) -679586, India
2Kerala University of Fisheries and Ocean Studies, Panangad, P.O., Kochi, PIN-682 506, India
Abstract
The effect of stocking density on the population structure, growth characteristics and production of
freshwater prawn Macrobrachium rosenbergii in coconut garden channels was studied. A randomised block design
of four treatments andfour replicates was used and the only difference being the stocking densities which ranged
from 5000ha-1 to 25,000ha-1. The mean weight and survival at the time of harvest varied from 55.5 g to 101.7 g and
28.21% to 69.44% respectively. At lower densities the proportion of undersized non-marketable prawns was
relatively low. However, net production increased with stocking density from 90.1 (TC-1) to 199.7 kg.ha-1.8 months-
1 (TC-4). Final marketable yield structure and economics revealed that the stocking density of 15,000ha-1 was
optimum for coconut garden channels in Kuttanad. Present study suggests that the profit incurred from freshwater
prawnfarming is directly related with production of larger orange-clawed and blue-clawed morphotypes. Hence
stocking density was found as an essential component for ensuring better marketable yield and improving the
economic returns. This study provides significant information since most coconut garden channels are abandoned
water areas which when utilised properly can be an additional source of income especially to agriculture farmers in
India and other Asian countries.
Introduction
Aquaculture production systems used across the world differ widely depending on the
species being cultured and on the geographical location and socio-economic context. The pursuit
for an alternate eco-friendly and sustainable aquaculture has led to the recognition of giant
freshwater prawn, Macrobrachium rosenbergii (De Man, 1879), with the trade name ‘scampi’,
as the prime candidate species for freshwater grow-outs. Kuttanad, the rice bowl of Kerala
(South India), is traditionally known as the home ground of this species. Traditionally, prawn
farming is carried out in polders developed from paddy cultivation (Kurup et al. 2002). Being a
low-lying wetland, Kuttanad is governed by a wide array of physico-chemical parameters
characterised by low water and soil pH. Since this area is also frequently flooded, a round the
year culture of scampi is not feasible. Moreover, paddy being given prime importance, scampi
culture is only practiced as part of a crop rotation process. Hence, the duration of culture cannot
be extended beyond 5-6 months. Also due to water logging, pre-stocking management practices
like drying, raking and liming of the soil cannot be done effectively. Hence, a wide fluctuation in
355 Asian Fisheries Science 24 (2011):354-366
the net production from these polders (95 to 1,297 kg.ha-1) was discernible (Kurup and Ranjeet,
2002).
Another limiting factor for the profitability of freshwater prawn farming is the size
disparity seen among adult prawns (Ranjeet and Kurup, 2002). The differential growth pattern of
various male and female morphotypes of M. rosenbergii has been well characterised in grow-out
population under different levels of stocking density and management strategies (Brody et al.
1980; Cohen et al. 1981; Karplus et al. 1987). As stocking density increases, an increase in yield
can also normally be expected; however, a corresponding increase of non-marketable prawns in
the harvested population due to the decrease in mean weight is commercially most
disadvantageous to this species (Cohen et al. 1981; Montanez et al. 1992; Kurup, 1996). Hence
the economic success of prawn culture in any locality is governed by the proper selection of
stocking density and stocking size (D’Abramo et al. 1989).
In Kuttanad, area under coconut cultivation is nearly 871,000 ha and intricate coconut
garden channels are available that provide a conducive grow-out environment for successful
farming operations. These channels usually have a water-spread area ranging from 0.2 to 7 ha,
hence providing a vast span of untapped resource for freshwater prawn farming. The farming of
this species has been carried out in the past without adhering to a strict protocol. No attempts
have so far been made to optimise the stocking density in these channels for improving survival
rate, growth performance, marketable yield and profitability. In the present study, an attempt is
made to investigate the optimum stocking density for freshwater prawn farming in coconut
garden channels of Kuttanad. Kuttanad shares a geographical and agro-climatic environment
similar to many South Asian countries. Sound knowledge on the farming of freshwater prawn in
the interstitial channels formed during agriculture can be effectively utilised as a means of
additional income to farmers.
Materials and Methods
A randomised complete block design method was used to select the channels. All the 16
coconut garden channels selected for the study had an equal water spread area of 1 ha each.
These channels were cleared of all predatory fishes by netting, drying and applying deoiled cake
of mahua @ 5 kg.ha-1. Lime @ 50 kg.ha-1was added to bring pH to neutrality. Having
considerable natural deposits of lime in these areas, liming @ 50 kg.ha-1 was found to be enough
to maintain the soil and water pH under control throughout the culture period. Farmyard manure
@ 1,000 kg.ha-1 was applied in equal monthly installments during the culture period. The
channels were stocked with post larvae procured from a local hatchery. The performance of post
larvae stocked under four separate stocking densities (treatments) in these channels was assessed.
Each set of treatment represents data collected from four separate channels (quadruplicates). In
the first set of treatments (TC-1) the initial stocking density was kept @ 5,000ha-1and in
subsequent treatments the initial stocking density was @ 10,000ha-1 (TC-2), 15,000ha-1(TC-3)
and 25,000ha-1 (TC-4) respectively. The prawns were fed initially with a commercial feed
(Charoen Pokphand (CP scampi) starter feed) @ 20% of the prawn biomass for 3 months and
later they were fed with a diet mixture of groundnut oil cake, rice bran and boiled meat of edible
Asian Fisheries Science 24 (2011):354-366 356
clam in equal proportion @ 10% of the prawn biomass. Water in the coconut garden channels
was exchanged twice every week. Water quality parameters such as temperature, dissolved
oxygen, transparency, water and soil pH were monitored on a monthly basis following AOAC
(1985), while levels of total ammonia-nitrogen (TAN), nitrite-nitrogen and hydrogen sulphide in
water samples collected during morning hours from each treatment were determined at
fortnightly intervals using Aquakit (MERCK).
At the end of 8 months of culture, water from the channels was pumped out, and the
prawns were harvested by handpicking. Random samples of 500-1,000 prawns from each grow
out were examined on the day of harvest. All the prawns were sorted according to their sex and
morphotypes (Kurup et al. 1998). The males were then classified into three morphotypes such as
small males (SM), strong orange-clawed males (SOC) and strong blue-clawed males (SBC) and
four of their transitional stages viz. weak orange-clawed males (WOC), transforming strong
orange-clawed males (t-SOC), weak blue-clawed males (WBC) and old blue-clawed males
(OBC). Similarly, females were also sorted into three main morphotypes such as small females
(SF), strong orange-clawed females (SOF) and strong blue-clawed females (SBF) and three
transitional stages viz. weak orange-clawed females (WOF), transforming strong orange-clawed
females (TOF) and weak blue-clawed females (WBF) (Harikrishnan and Kurup, 1997). All the
prawns were measured up to the nearest mm and weighed up to the nearest g. In order to assess
the effect of stocking density on population characteristics and yield structure the cumulative
mean values of each treatment among channels (TC-1 to 4) were compared. The variations in the
mean weight, survival rate and net production among the four treatments were tested employing
Duncan’s Multiple Range Test (DMRT) (Gomez and Gomez, 1984).
Results
Water quality parameters among the treatments did not show any significant difference
(P>0.05). Table 1 shows the mean values calculated for different water quality parameters
observed during the present study. All the water quality parameters determined were well within
the optimum ranges.
Population structure
The details of population density at harvesting on mean weight of prawns, percentage
survival and contribution of male and female in the harvested population of the four treatments
(TC-1 to TC-4) are given in Table 2. The final densities of M. rosenbergii at the time of harvest
in treatments 1 to 4 were in the order of 0.35, 0.54, 0.57 and 0.70 m-2 respectively. Survival in
the various treatments showed a remarkable decline from 69.4% in TC-1 to 28.2% in TC-4. A
similar declining trend in the mean weight also was noticed with increase in final density among
the treatments. Male: female ratio was dissimilar at all the four densities. Highest production was
encountered in TC-4 (199.7 kg.ha-1), while the least was seen in TC-1 (90.1 kg.ha-1). The
percentage by weight of undersized non-marketable prawns (SM and WOC) increased
remarkably with an increase in the stocking density (Table 3). Proportion of SM and WOC was
least in TC-1 (10.32%), whereas it showed significant increase to 36.33% in TC-4. On the
357 Asian Fisheries Science 24 (2011):354-366
contrary, percentage of BC males in the final population followed an inverse trend, which
showed a decrease at significant levels from 34.71% in TC-1 to 14.11% in TC-4. Among the
female morphotypes, only SF showed a direct relationship with stocking density as its proportion
increased from 5.33 in TC-1 to 12.89% in TC-4. The most significant among them were the
individual weight of OBC, which showed reduction from 147.9 to 103.45 g in TC-1 and TC-4
respectively.
Results of Duncan’s Multiple Range test (DMRT) employed to compare mean weight,
survival rate and net production indicate that all the above production parameters were
significantly (P<0.01) different among the four treatments (Table 4). On further investigation it
was noticed that mean weight and survival rate among all the four treatments varied significantly
(Table 5). However regarding the net production the performance of TC-1 and TC-2 did not
differ significantly. Similarly, there was no difference in the net production between TC-3 and
TC-4. The structure of male and female populations from four treatments is depicted in Fig. 1. It
could be seen that SM and WOC showed a direct proportion with the increasing density. The
proportion of SM was appreciably high in stocking density of @ 25,000ha-1 (14.2%) while it was
least at a density of 5,000ha-1(7.8%). Similarly, high proportions of t-SOC and OBC were
observed at lower density of 5,000ha-1 (26.8% and 15.1% respectively) while their percentage
showed reduction considerably at stocking density 25,000ha-1 (16.3% and 12.8% respectively).
The population structure of female morphotypes at the final harvest also showed significant
variations (P<0.05) in the different treatments (Fig. 1). The percentage of undersized SF
increased from 10.1 to 15.3% as the stocking density increased from TC-1 to TC-4. The
percentage of orange-clawed (OC) and blue-clawed (BC) females did not follow any particular
pattern among the treatments, but their adequate representation in TC-2 (39.8 and 49.7%) and
TC-3 (41.2 and 45.2%), were worth noticing.
Table 1. Water quality parameters from the four treatments 1-4 (Coconut garden channels).
Parameters
Treatment 1
(TC-1)
Treatment 2
(TC-2)
Treatment 3
(TC-3)
Treatment 4
(TC-4)
Temperature (oC)
28.4 ± 2.35
29.3 ± 2.77
31.4 ± 1.52
30.4 ± 2.12
Dissolved Oxygen (mg.L-1)
4.62 ± 1.62
5.50 ± 0.84
5.06 ± 0.91
4.94 ± 1.02
pH range
7.8 ± 0.46
7.7 ± 0.52
7.4 ± 0.64
7.5 ± 0.55
Soil pH range
6.3 ± 0.34
6.0 ± 0.25
6.2 ± 0.28
6.3 ± 0.40
Transparency (cm)
35.1 ± 12.41
28.8 ± 18.65
26.2 ± 11.30
28.4 ± 13.88
Total alkalinity (mg.L-1)
68.4 ± 14.42
52.1 ± 13.15
66.7 ± 18.99
64.3 ± 15.38
Nitrite-N (mg.L-1)
0.11 ± 0.05
0.14 ± 0.03
0.12 ± 0.04
0.11 ± 0.03
Total ammoniacal-N (mg.L-1)
0.14 ± 0.01
0.17 ± 0.03
0.13 ± 0.05
0.09 ± 0.03
Mean water quality parameters +/- standard error from four treatments in quadruplicate (N=128)
Asian Fisheries Science 24 (2011):354-366 358
Table 2. Stocking details and yield characteristics of M. rosenbergii reared under stocking density in coconut garden
channels.
TREATMENTS
TC-1
TC-2
TC-3
Stocking Particulars
Number per ha.
5,000
10,000
15,000
Mean weight (g)
0.2
0.2
0.2
Biomass per ha.
1.0
2.0
3.0
Harvest Details
Number per square meter
0.35
0.54
0.57
Number per ha.
3560
5380
5690
Mean weight (g)
101.65
87.73
69.11
Gross production (kg.ha-1)
92.10
110.10
188.30
Net production (kg.ha-1)
90.10
103.16
173.50
Survival (%)
69.44
54.52
42.69
Mean male weight (g)
128.6
105.2
101.8
Mean female weight (g)
68.2
52.5
50.1
Sex ratio
2.05:1
1.15:1
1.11:1
Fig. 1.Population structure of male and female morphotypes in treatment 1-4.
Fig 1. Population structure of male and female morphotypes in
treatment 1-4
0%
20%
40%
60%
80%
100%
TC-1 TC-2 TC-3 TC-4
Treatments
Percentage contribution
SBF
WBF
TOF
SOF
WOF
SF
OBC
SBC
WBC
t-SOC
SOC
WOC
SM
359 Asian Fisheries Science 24 (2011):354-366
Table 3. Percentage contribution and mean weight of male and female morphotypes among the four treatments (channels).
Treatment
Male morphotypes
Female morphotypes
SM
WOC
SOC
t-SOC
WBC
SBC
OBC
SF
WOF
SOF
TOF
WBF
SBF
TC-1
Sample size (n)
65
25
6
72
41
22
24
29
34
15
26
51
50
Contribution by weight (%)
6.28
4.04
4.56
28.45
5.00
8.37
21.37
5.33
1.16
0.10
7.34
4.76
3.24
Mean weight (g)
18.41
42.53
93.33
103.62
97.78
129.40
147.91
12.05
34.64
51.50
52.14
54.59
76.80
TC-2
Sample size (n)
24
14
17
45
48
35
52
24
48
4
15
24
24
Contribution by weight (%)
15.79
11.28
3.77
20.12
6.22
6.20
15.09
7.37
0.81
0.42
3.55
4.47
4.91
Mean weight (g)
25.60
32.20
87.50
108.70
82.80
120.53
121.30
12.26
37.92
50.45
58.17
51.18
65.41
TC-3
Sample size (n)
13
24
15
35
31
20
35
24
42
15
12
16
62
Contribution by weight (%)
20.21
15.92
2.66
11.58
8.02
4.20
10.62
9.33
0.52
0.14
7.87
3.55
3.38
Mean weight (g)
18.23
36.43
68.50
76.37
78.12
102.45
111.45
16.04
31.50
60.63
71.99
60.95
70.00
TC-4
Sample size (n)
29
29
13
30
51
33
40
33
38
18
29
17
32
Contribution by weight (%)
23.66
12.67
3.73
14.29
4.42
2.00
7.69
12.89
1.72
1.56
5.88
6.34
2.15
Mean weight (g)
15.57
32.47
45.61
61.57
61.00
95.34
103.45
13.50
41.20
64.40
58.40
61.14
86.02
Asian Fisheries Science 24 (2011):354-366 360
Table 4. Comparison of means for mean weight of prawn, survival rate and net production among the four
treatments.
Variable
Source
df
Sum of
Squares
Mean Square
F
Sig.
Mean
weight
Between Treatments
3
4956.183
1652.061
30.773
0.001
Within Treatments
12
644.234
53.686
Total
15
5600.416
Survival
Between Treatments
3
3680.498
1226.833
47.036
0.001
Within Treatments
12
312.993
26.083
Total
15
3993.491
Net
production
Between Treatments
3
34100.544
11366.848
16.502
0.001
Within Treatments
12
8265.883
688.824
Total
15
42366.427
Table 5. DMRT results for mean weight, survival rate and net production among the four treatments.
Treatment
Mean weight
Survival
Net production
Mean
SD
Mean
SD
Mean
SD
TC-1
101.650a
7.5067
69.440a
6.6525
90.100b
7.4891
TC-2
87.730b
8.1917
54.533b
3.8724
103.160b
15.0562
TC-3
69.113c
8.6865
42.690c
6.3707
173.500a
28.4177
TC-4
55.483d
3.9793
28.210d
2.1198
199.718a
40.8038
Means with same letter as superscript are homogeneous
Yield Characteristics
Variations in the mean weight of population corresponding with final density were
observed among the four treatments. Highest mean weight for prawns was recorded in TC-1
(101.6 g) against 55.5 g registered in TC-4 (Table 2). Invariably, the mean weight of male and
female morphotypes was highest in TC-1 with 128.6 g and 68.2 g respectively in TC-1 and 85.3
and 42.8 g respectively in TC-4. Commensurating with the variations in mean weights, the net
production also showed differences among the treatments. The lowest mean net production was
recorded in treatments with stocking density @ 0.5 m-2 (90.1 kg.ha-1), while the highest
production was registered in channels stocked @ 2.5m-2 (199.7 kg.ha-1). The results of DMRT
(Table 5) showed variations in net production were insignificant among TC-1 and TC-2 and
between TC-3 and TC-4. Hence, there was no significant increase in the net production beyond
an initial stocking density of 15,000 ha-1 in these coconut garden channels. It may, therefore, be
inferred that a further increase in the stocking density from 1.5to 2.5m-2 will not have any
significant effect in improving the net production.
The weight distribution patterns of prawns in the four treatments at different levels of
stocking density are depicted in Fig. 2. Preponderance of males in the final harvest in TC-1
361 Asian Fisheries Science 24 (2011):354-366
seems to have influenced the marketable weight structure which is evident from the dominance
of weight group >120 g (44%). Moreover, it may also be noted that the percentage of undersized
non-marketable prawns (<50 g), such as SM, WOC and undersized female morphotypes were
appreciably low (6%) in this treatment. In contrast, the percentage of non-marketable prawns
showed an increase to 22% in TC-4, which was characterized with highest stocking density.
Furthermore, the weight class >120 g was only moderately represented (29%) in TC-3 and TC-4.
In these treatments, the weight distribution of the total population was found to be much
influenced by the female morphotypes since the weight group 5080g (40%) showed
predominance. It would thus appear that of the total biomass produced from each of the four
treatments, 94% of the yield from TC-1 was constituted by prawns of >50g size group and
therefore, were marketable whereas in TC-4 only 78% were marketable. While working out the
total revenue by taking into consideration the price packages offered by the seafood processing
plants located at Cochin for M. rosenbergii per kg, total income would work out to be Rs.
25,032/- in TC-1, Rs. 32,312/- in TC-2, Rs. 47,528/- in TC-3 and Rs. 60,120/- in TC-4. It may
therefore be seen that though the yield from TC-1 formed only 35.7% of TC-4, income wise it
fetches 43.3% of the latter because of large size of prawns as well as reduction in the percentage
of undersized prawns. However, analysis of cost and return per ha showed beyond a stocking
density of 15,000ha-1 the profit incurred from farming reduced considerably (Table 6). As the
stocking density increased in subsequent treatments the gap between the percentage contribution
of yield and income reduces significantly. Hence beyond a stocking density of 15,000ha-1, the
farming of freshwater prawn becomes less economical.
Fig. 2. Market yield structure of final harvest from four treatments.
Fig. 2. Market yield structure of final harvest from four
treatments
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
TC-1 TC-2 TC-3 TC-4
Treatment
Percentage contribution
>230
120-230
8-0-120
60-80
50-60
<50
Asian Fisheries Science 24 (2011):354-366 362
Table 6. Cost and returns per hectare from M. rosenbergii farming under separate stocking densities in coconut
garden channels.
*1 Rs= 0.22
US$
Discussion
A remarkable difference in growth and the consequent weight attained by the
morphotypes at the four levels of final density in coconut garden channels could be discernible
and their variations were well reflected in the population structure. The available reports suggest
that females invariably dominate in grow-outs of M. rosenbergii (Smith et al. 1978). However, in
the present study, a similar trend was noticed only at higher final population density levels in
coconut garden channels, while at low stocking densities, males showed their dominance. The
growth rate of female is slow when compared to their male counterparts and therefore the
chances of their vulnerability to predation are high in higher density, especially during early
phase of culture (Peebles, 1979). Adult male prawns at a greater stocking density are prone to
face competition for food and space. Owing to greater struggle and due to its highly cannibalistic
nature, the proportion of male population gets considerably reduced (Kurupet al. 1998). Retrieval
percentage registered in the coconut garden channels in the present study was found to be high
when compared to earlier reports (Padmakumar et al. 1992; Mathew et al. 1993). Mean weight of
dominant male morphotypes in the highly stocked grow-outs increased with reduction in survival
rate and this may be due to the complex social hierarchy prevailing in the grow-out, while the
Particulars
TC-1
TC-2
TC-3
TC-4
I. COSTS (Rs.)
A. Variable Cost
Pond preparation
2520
2850
3500
5000
Fertilizer
520
520
800
1000
Feed
3500
3500
6500
9000
Seed
3000
6000
9000
15000
Power
1200
1025
1230
2210
Labor
1800
2900
5000
7800
Fuel
850
850
1250
2000
Total Variable Cost
13390
27280
42010
B. Fixed Costs (Rs.)
Pond Construction (apportioned)
7500
7500
7500
7500
Depreciation (5%)
375
375
375
375
Salary.Wages-1
1500
1500
1500
1500
Interest on Fixed capitals (18%)
1773
1773
1773
1773
Total Fixed Costs
11148
11148
11148
11148
C. Total Costs (A+B) (Rs.)
24538
28793
38428
53158
II. RETURNS
Total cost of production (Rs.)
24538
28793
38428
53158
Total Yield (kg)
89.4
115.4
182.8
250.5
Gross Return (Rs.)
25032
32312
47528
60120
Net Return (Rs.)
494
3519
9100
6962
363 Asian Fisheries Science 24 (2011):354-366
undersized SM and WOC were deprived of food and space. This in turn reduced their average
weight at higher densities.
Earlier works to optimise stocking density in polders (Kurup et al. 2002), river pens (Son
et al. 2005), cages (Cuvin-Aralar et al. 2007) and in polyculture ponds (Hossain and Islam 2006;
Marques et al. 2010) suggest that the most important factor for viable freshwater prawn culture is
stocking density. A dynamic shift in the proportion of male morphotype with density was also
discernible in the present study. At higher density, the proportion of SM was relatively high
while OC males and its transitional stages showed next hierarchical dominance. Interestingly in
the channels having low density, the percentage of BC males was distinctly high but the weight
attained by them were comparatively lesser than that of t-SOC. This may be because with an
ambient environment to thrive, the undersized male prawns instead of passing through the
transformation pathway skipped the intermediary stages to attain the terminal growth by leapfrog
transformation (Harikrishnan and Kurup, 1997). Moreover, in higher densities because of the
urge for faster transformation from SOC to t-SOC and to subsequent BC, the relative size and
weight of these males became comparatively less. So even though the prawns could attain the
terminal stage of their growth, the weight gained was pertinently less when compared to
morphotypes from lower densities. The shift observed in the frequency of male morphotypes
may be due to the complex social organisational hierarchy in M. rosenbergii. At high density the
percentage of SM and WOC were high and this would suggest the chances of inhibition of
growth of SM by BC due to the proximity of the latter. It may therefore be inferred that the rate
of transformation of male morphotype to its successive stages was very rapid in low density
grow outs, on account of less competition and fast growth rate and this can well be attributed as
the reason for the presence of OBC in appreciably high proportions. Selective stocking and
harvesting hence of late have received much attention among researchers as a mode to reduce
this size disparity (Mohanty, 2009; Preto et al. 2010).
The inverse relationship between the prawn density and mean size of different
morphotypes in this study fully agrees with the earlier findings (Cohen et al. 1981; Karplus et al.
1986b). The reduction in prawn growth with increasing density may be attributed to a variety of
reasons such as competition for food, early sexual maturity, hyperactivity of subordinate
individual, loss of exuvia and aggressive and social hierarchy (Karplus et al. 1986a). The results
from the present study suggest the relative proportion of OC and BC in the population and the
marketable size structure of the yields profoundly influence the economic viability of ‘scampi’
farming, rather than the total biomass produced. Therefore, information on the effect of various
stocking densities, management measures and dynamics of male morphotypes and their
interaction are very much required for improvement in the economic yield of M. rosenbergii for
sustainable aquaculture. While working out the marketable yield structure and profit incurred
from the culture under varied stocking densities, it could be seen that an increase in stocking
density beyond a particular level was not helpful in the reciprocal improvement of the profit due
to the dominance of undersized prawns in the final harvest. Although the significance of
formulating different feeding strategy for diverse stocking rates has been advocated recently
(Asaduzzaman, 2009), optimisation of stocking density is still considered the pivotal point in
developing a threshold grow-out strategy for M. rosenbergii in many Asian countries (Schwantes
Asian Fisheries Science 24 (2011):354-366 364
et al. 2009; Nazim et al. 2010). Optimisation of stocking density also holds good since the
reduction of the stocking rate below a particular level, though helpful in increasing the mean
weight of prawns, would result in poor yield and thus farming becoming economically unviable.
Ranjeet and Kurup (2008) has shown that under similar culture period, the mean weight of prawn
from polders and coconut garden channels differ greatly hence emphasising the need for
adopting suitable grading system for marketing and increasing economic profitability from M.
rosenbergii farming.
Farming in coconut garden channels was found to have some advantages like (1) Longer
duration of culture than polders, as a result the mean weight of prawns gets increased (2) Better
monitoring of feed input and hence wastage of feed can be considerably reduced (3) An
elaborate network of coconut roots available on the banks on the channel act as artificial
substrate or shelters for prawn hence reducing cannibalism (4) The shade cover of coconut palm
avoids any thermal stratification in channels, (5) Harvesting is less labour intensive and can be
done through draining or pumping out the water and (6) Since channels can be individually
harvested, the farmer can sell the catch depending on the market demand.
Conclusion
In Kuttanad, a scientific culture practice for M. rosenbergii in coconut garden channels is
lacking and most of the farmers are complying with a rather traditional type of farming which
leads to reduced profit. Since stocking density has been a deciding factor that determines the
profitability and economic sustainability of prawn farming, any information on standardising
stocking densities for these grow-outs warrants much importance. The present study suggests
that the relative proportion of larger OC and BC morphotypes in the final population profoundly
influences the economic viability of ‘scampi’ farming in coconut garden channels. In order to
ensure the availability of desired morphotypes in the harvested population in appreciable
quantities, optimisation of stocking density is a prerequisite. While maintaining an initial
stocking density at 1.5m-2 in coconut garden channels, a linear relationship between the
economic returns and corresponding profit could be established and similar relationship could
not be arrived at other stocking densities studied. Therefore, a stocking density of 15,000 ha-1
would be ideal in the coconut garden channels of Kuttanad for the farming of M. rosenbergii in a
more economically viable level.
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Received: 01/03/2011; Accepted: 23/08/2011 (MS08-71)
... In terms of the intensification of culture for freshwater prawns, stocking density and culture strategies are the main factors that contribute to estimating production and survival at this higher level of culture intensity because the majority of growth performance parameters tend to be critical under these factors (Sanchez-Zazueta et al. 2013). Studies on the effect of stocking density in freshwater prawn culture have been carried out in coconut garden channels (Ranjeet and Kurup 2011), circular tubs (Langer et al. 2011), fiberglass tanks (Banu et al. 2016), aquarium (Costa and Arruda 2016), earthen ponds (Paul et al. 2016;Chowdhury et al. 2017), biofloc systems (Negrini et al. 2017), and net cage-concrete pond systems (Avillanosa et al. 2019) for the giant freshwater prawn. The highest productions were observed in densities ranging from 1.5 to 3.0 prawns/m 2 in semi-intensive systems and from 5 to 50 prawns/m 2 in intensive systems. ...
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