Project Technical Report:" Development of clam culture for improvement and diversification of livelihoods of the poor coastal communities in Central Vietnam - MS4 " potx

Ministry of Agriculture & Rural Development

Collaboration for Agriculture & Rural Development
(CARD)









027/05VIE

Development of clam culture for improvement
and diversification of livelihoods of the poor
coastal communities in Central Vietnam


MS04: 3
rd
Six-Monthly Report





April – October, 2007

1
Table of Contents

1. Institute Information 3
2. Project Abstract 4
3. Executive Summary 4
4. Introduction & Background 6
5. Progress to Date 6
5.1 Implementation Highlights 6
5.1.1 Clam production (Grow-out trials) 6
5.1.2 Hatchery production 8
5.1.3 Propagation of the technologies (on farm trials level) 16
5.2 Smallholder Benefits 16
5.2.1 Opportunity to utilize the brackish water ponds for clam production 16
5.2.2 Increasing in production and benefit from clam culture in the intertidal areas 16
5.2.3 Easily Applicable Farming Knowledge 16
5.2.4 Low Investment Risk 16
5.2.5 Maximizing Commercial Potential through Knowledge 16
5.3 Capacity Building 17
5.3.1 ARSINC 17
5.3.2 End-users 18
5.3.3 Enhanced reputation and relation ship with other institutions and collaborators
18
5.4 Publicity 18
5.5 Project Management 18
6. Report on Cross-Cutting Issues 18
6.1 Environment 18
6.2 Gender and Social Issues 19
7. Implementation & Sustainability Issues 19
7.1 Issues and Constraints 19

7.2 Options 19
7.3 Sustainability 19
8. Next Critical Steps 19
9. Conclusion 19
10. Statuatory Declaration 20


2
1. Institute Information
Project Name
Development of clam culture for improvement
and diversification of livelihoods of the poor
coastal communities in Central Vietnam.
(Project No: 027/05VIE)
Vietnamese Institution
Aquaculture Research Sub-Institution for North
Central (ARSINC)
Vietnamese Project Team Leader
Mr. Nhu Van Can (Project Director)
Mr. Chu Chi Thiet (Project Manager)
Australian Organisation
South Australian Research and Development
Institution (SARDI)
Australian Personnel
Dr Martin S Kumar (Team Leader)
Dr Bennan Chen (Senior Scientist)
Date commenced
February 2006
Completion date (original)
February 2009

Completion date (revised)

Reporting period
November 2006, April 2007

Contact Officer(s)
In Australia: Team Leader
Name:
Dr Martin Kumar
Telephone:
08 82075 400
Position:
Principal Scientist, and Program
Leader,
Integrated Biosystems
Integrated Resource Management
and Biotechnology
Fax:
08 82075481
Organisation
South Australian Research and
Development Institution (SARDI)
Email:
kumar.martin@saug
ov.sa.gov.au

In Australia: Administrative contact
Name:

Telephone:

Position:

Fax:

Organisation

Email:


In Vietnam
Name:
Nhu Van Can
Telephone:
+84.383829884
Position:
Director
Fax:
+84.383829378
Organisation
Aquaculture Research Institute for
North-Central
Email:



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2. Project Abstract

3. Executive Summary
The.
• The stocking biomass of 2 ton/ha is recommended for optimising cost benefits in clam
production under intertidal culture conditions.
• Successful production of clam as a rotational crop in prawn farms provides new
opportunity for the farmers to utilise the prawn farm which normally used only for 4
months per year for shrimp culture.
• Artificial conditioning of clam brood stock has been successfully completed
• The mass production of 2 million spat was achieved under revised larval rearing
procedure developed.

The main objective of the project is to develop and extend the clam culture technology
(hatchery and husbandry) to sustain livelihoods of poor coastal farmers in the North
Central provinces and to develop a strategy which contributes to sustainable aquatic

environment management using clam aquaculture to improve prawn farm effluent
utilisation. In the first half of the second year, two types of clam production trials
(intertidal clam production, clam production in prawn ponds as rotational crop) and
broodstock conditioning trials have been successfully completed. Details of the both
production trials along with brood stock conditioning results are included in this report.
Key findings are listed below.

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3.1 Project Implementation Progress
3. 1.1 Key Highlights
Project progressed well during the last 18 months and achieved specified milestones related
to the technology development in clam husbandry (production) and hatchery areas.
Following milestone reports submitted were reviewed and accepted.
• Socio-economic evaluation report
• 1
st
six monthly report
• 2
nd
six monthly report
In the first half of the second year, two clam production trials including; intertidal clam
production, clam production in prawn ponds as rotational crop, broodstock conditioning
have been successfully completed. Details of the both production trials along with brood
stock conditioning results are included in this report. A farmer selection criterion was
developed in consultation with lead farmers, village representatives and provincial
authorities. The details will be reported in the next 4
th
six monthly report.
In the second year, the work will be concentrated on farm trials, which fine tune the
technology and facilitate formulation of extension manuals. In the third year, work will focus

on extension of technology including expanded farmer participated trials. Project impact will
also be assessed during the third year
3.1.2 Key outcome
a) Production experiments made excellent progress
• Optimisation parameters for intertidal clam production have been determined. The
stocking biomass of 2 ton/ha is recommended for optimising cost benefits in clam
production under intertidal culture conditions.
• Viability of clam production in prawn pond as a rotational crop has been established.
Successful production of clam as a rotational crop in prawn farms provides new
opportunity for the farmers to utilise the prawn farm which normally used only for 4
months per year for shrimp culture.
b) Hatchery production experiments.
Based on the results of initial larval rearing experiments, a second mass spat production trials
successfully completed by producing 2 million spats. Artificial conditioning of clam brood
stock has been successfully completed
Experimental design on larval rearing and nursery production has been revised based on this
trial results. Larval rearing and brood stock conditioning experiments are in progress.


c) On farm trials/Demonstration.
An introductory workshop on clam culture has been conducted for the farmers in the North
Central Provinces. Farmer selection criteria for demonstration were prepared. Lead farmers
were selected. Trials are under way. Further workshops are being organised to provide
guidelines on demonstration trials to farmers.
Overall the project is progressing well as per the proposal.

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4. Introduction & Background
The main objective is to develop and extend the clam culture technology (hatchery and
husbandry) to sustain livelihoods of poor coastal farmers in the North Central provinces; and

to develop a strategy which contributes to sustainable aquatic environment management
using clam aquaculture to improve prawn farm effluent utilisation. The aims of the proposed
project are:
a) to provide poor fisher community an alternative income, food security;
b) to improve technological and extension capacity for the stakeholders; and
c) to reduce negative impacts of shrimp culture through implementation of a strategy for
environmental management and waste utilisation of existing resources.
4.1. Specific objectives:
The objectives of this project (027/05VIE) include the following:
• to develop and extend the clam culture technology (hatchery and husbandry);
• to sustain livelihoods of poor coastal farmers in the North Central provinces; and
• to develop a strategy which contributes to sustainable aquatic environment management
using clam aquaculture to improve prawn farm effluent utilization.
4.2. Outputs Expected
In accordance with expected output proposed, the last six months were focused on following
aspects related on the following
- Completed intertidal clam production trial
- Completed rotational clam in prawn farm
- One set of mass production trials completed, Larval rearing experiments to optimize
the larval survival and growth is in progress.
- Brooder conditioning experiments completed
- Farmer selection criteria for demonstration was developed

4.3. Methodology
The visits by Australian Project Leader in April 2007 enabled to undertake major review of
the results obtained on clam production and larval rearing trials and also enabled to fine tune
the experimental procedure for larval rearing and nursery production optimization. Team
workshop was organised in April enable to evaluate the clam production results and larval
rearing methods. Larval rearing and nursery productions experiments were revised and the
trials are in progress. Demonstration trials, design, planning, farmer selection criteria and

execution procedures were finalised.
5. Progress to Date
5.1 Implementation Highlights
5.1.1

Clam production (Grow-out trials)
The research in pond culture type will be focused on suitability of substrate, optimum
stocking density, and stocking size. All experiments were conducted in triplicate. The
outcome of the experiments (culture types) will be used for the development of technical

6
guidelines for on farm trials in the second year. The clam production involved the following
5 types culture trials:
a) Clam culture using prawn farm influent water (reservoir): Clam culture was carried
out as a pre- treatment for water intake in prawn farm. Work completed and the
results reported
b) Clam culture using prawn farm effluent (effluent treatment pond). Clam culture was
conducted by utilising prawn farm effluent. Work completed and the results reported.

c) Shrimp and clam polyculture: Simultaneous culture of prawn and clams was
undertaken with a view to improve farm water quality as well as generate additional
income. Work completed and the results reported.
d) Alternative/rotation crop: Clam culture was under taken after the pawn harvest as
rotational crop. Work completed and results included in this report.
e) Clam culture in intertidal area: Inter tidal area was used for clam culture. Work
completed and the results included in this report.

5.1.1.1 Experiment on clamcultured in the intertidal areas

Traditional clam culture has been undertaken in the inter-tidal areas. The aim of this

experiment was to enhance the profitability of clam farmer. The key objective was to
increase productivity and benefit by determining the optimum stocking density and stocking
size. The other parameters within the culture system can not be altered as it is a natural
ecosystem highly connected to capture fisheries which is one of the key industry for the
fisher community.

Materials and method
The inter-tidal clam culture experiment was undertaken in 24 plots of 50 m
2
each for 8
treatments (3 replicates each). The small size of clam seed (1.0 cm) were stocked at 4
different stocking biomass 0.5, 1.0, 2.0 and 3.0 tons/ha and referred as T1, T2, T3 and T4
respectively. The bigger size of clam seed (1.7 cm) were stocked at 4 different stocking
biomass of 3.4, 6.8, 13.6 and 20.6 ton/ha and referred as T5, T6, T7 and T8 respectively (the
densities were adjusted due to actual stocking size availability). Experiment was terminated
after 165 days rearing.
The environment factors such as temperature, DO, pH and turbidity , salinity of water in the
experiment site were monitored daily at 3 designated points within the experimental area
while samples of water were analysed weekly for Total N, Total P, Ammonia and Nitrate.
Growth of clam, expressed in mean of height (cm) and mean of weight (gr), was determined
by random sampling (n=30) and measured every fortnight. The daily specific growth rate
(SGR) was calculated using the following formula:
SGR(%/day) = 100*(LnW
f
-LnW
i
)/t
Where: W
i
and W

f
are mean of initial weight and final weight, respectively and t is number
of experiment days.
The final production (expressed as ton/ha) of each treatment was conducted by entirely
harvested and the biomass gained was calculated from final production minus the stocking
biomass.
Size variation was evaluated according to (Wang et al., 1998) in which the mean of three
replicates of the coefficient of variation (CV) was used to examine the inter-individual

7
weight variation among the clam in each treatment: CV(%)=100*SD/ M where M is mean of
weight and SD is standard deviation of the clam in each treatment.
The meat ratio (% of meat weight/ total weight) of clam estimated to understand meat yield.
This parameter was measured by random sampling of clam and the total weight of the clam
and meat weight was measured by separating the meat content. The excess water was
removed by putting the sample on tissue papers.
The fatty acids content of clam was determined from random samples, preserved in Liquid
Nitrogen Biological Container (YDS-3, -196
o
C). The samples then were analysed by
extracting the fatty acid in methanol/toluene mixture (3:2 v/v) and analysed in Finnigan
Trace GC untra, capilary collume BP-70 (50m x 0.32mm x 0.25µm) in the Laboratory of
Vienamese Academy of Science and Technology.
All data of the treatments were tested for significant differences (p<0.05 or p<0.01) using
One-way ANOVA followed by Turky test for multiple comparisons of means. The data are
expressed as Average ± SD and statistical analyzed was performed using GraphPad Prism
version 4.0 and Microsoft Office EXCEL for Window.

Results and discussions
1.1 The environment conditions of the experiments

The experimental site in the intertidal area is situated in Hau Loc District, Thanh Hoa
Province near the estuary where clam naturally occurred. The environment conditions such
as DO, water temperature, pH and salinity (table 1) are regarded as the best conditions for
clam development. The high levels of salinity fluctuation are typical for estuary ecological
conditions. This means clam are not be affected by the marked variation in the salinity and
good growth and survival rate noticed. The average water temperature was 23.59±2.40
o
C s.
Table 1. Environment conditions in the cultured areas
Paramenters DO (ppm) Water
temperature (
o
C)
pH Salinity (ppt) Turbidity (cm)
Aver 6.25±0.42 23.59±2.40 25.65±2.84 9.05±3.13
Max 7.66 31.00 8.99 31.00 20.00
Min 5.50 19.50 7.21 20.00 5.00
1.2 Growth performance
The growth performance of the two stocking sizes of clam at different stocking biomass
expressed in specific growth rate, final length and final weight are shown in the table 2 and
table 3.
Table 2. Growth performance of clam at stocking size of 1.0cm
Treatments T1 T2 T3 T4
SGR 1.25±0.05
a
1.13±0.05
a
1.08±0.10
ab
0.94±0.37

b

Final length (cm) 2.04±0.13
a
2.01±0.09
ab
1.95±0.10
b
1.95±0.11
b

Final weight (gr) 5.92±1.08
a
5.76±0.81
ab
5.46±0.76
ab
5.30±0.85
b

% of meat/total weight 15.87±1.00
a
15.48±2.72
a
15.53±1.02
a
15.15±5.47
a
CV% (weight) 28.72±2.55
a

23.07±0.24
b
23.73±1.55
b
27.78±2.11
ab

Value (Mean±SD) followed by different superscript letters within a row are significantly different (P<0.05). T1,
T2, T3, T4 are treatments of clam cultured at 0.5, 1.0, 2.0 and 3.0 tons/ha respectively. SGR = daily specific
growth rate; CV = coeficient of variation


8

9
For the small size of clam (1.0cm), there was no significant difference in specific growth rate
among T1, T2 and T3 treatments (table 2) indicating that growth of the clam was not be
affected by the stocking biomass below 2 tons/ha. The final size of clam was more variable at
low (T1) and high (T4) levels of stocking density compared to the medium ones. The meat
yield expressed in percentage of meat per total weight, which regarded as the most valuable
part of clam was not significant different (p>0.05) in all treatments.
Table 3. Growth performance of clam at stocking size of 1.7cm
Treatments T5 T6 T7 T8
SGR 0.62±0.04
a
0.46±0.03
b
0.33±0.02
c
0.32±0.02

cd

Final length (mm) 2.36±0.17
ab
2.40±0.10
a
2.32±0.11
bc
2.27±0.10
c

Final weight (gr) 9.24±1.20
a
9.33±0.95
a
8.90±1.12
a
8.21±1.01
b

% of meat/total weight 14.53±1.89
a
15.78±2.35
a
16.53±0.62
a
15.48±1.31
a

CV% (weight) 22.3±0.45

a
19.05±5.16
a
18.69±3.36
a
22.73±4.16
a

Value (Mean±SD) followed by different superscript letters within a row are significantly different (P<0.05). T5,
T6, T7 and T8 are treatments of clam cultured at 3.4, 6.8, 13.6 and 20.6 ton/ha respectively. SGR = daily
specific growth rate; CV = coeficient of variation

The growth performances of 1.7 cm clam stocked at different densities are provided in table
3. In the case of 1.7 cm clams, the increase in stocking biomass significantly impacted
specific growth rate. At the stocking density higher than 3 tonnes/hectre, the SGR was
relatively low and was not significantly different for T7 and T8 treatments. The final length
and final weight of the T8 treatment were significantly smaller than the other treatments.
Generally, at younger stage, animal grow at a faster rate. In the case of clam, the small size (1
cm) the growth was significantly better than the bigger size (1.7cm) if stocked at same
biomass. In the intertidal areas, the natural feed and environmental factors are uncontrollable
and are dependent of nature. Dynamics of tide, wave and current create the availability of
algae, organic matter that regarded as feed for clam. However, clam is a filter feeder and
passively dwells on the bottom therefore, increase in biomass beyond certain level, the
natural feed might not be enough for growing. Results of growing performance (table 3)
indicated that at high stocking biomass (3 ton/ha), the growing could be inhibited as it was
evidenced that the grow rate was significantly reduced as in creasing of stocking biomass. It
also is noted that the culture period is winter time of the year when water temperature
normally is low and not appropriate for growing of M. lyrata, the tropical species.
1.3 Survival
The stocking biomass impacted the survival rate in both sizes of clams stocked. Survival was

very high in the low stocking biomass and was almost similar in the treatment T2 and T3.
The survival rate in T1 and T4 treatment was significant different (P<0.05). In the bigger size
groups, the T7 and T8 treatments resulted in very low survival and not significant different
compared to the treatment T5 and T6. The environmental condition and food availability
could be attributed as main reason for the impact stocking biomass on survival rate.

T1 T2 T3 T4
50
60
70
80
90
100
110
a
ab
ab
b
Clam at stocking size of 1.0 cm
Survival (%)

T5 T6 T7 T8
50
60
70
80
90
100
110
a

b
c
c
Clam at stocking size of 1.7 cm
Survival (%)
Fig 1. Survival of clam size 1.0cm and 1.7cm rearing at different stocking biomass.
Valu , T3
1.4 Production and quality
ated from both growth and survival. There was a positive
T3 T4
e (Average ± S.D) followed by different superscript letters are significantly different (P<0.05). T1, T2
and T4 are treatments of clam cultured at 0.5, 1.0, 2.0 and 3.0 tons/ha respectively; T5, T6, T7 and T8 are
treatments of clam size 1.7cm cultured at 3.4, 6.8, 13.6 and 20.6 ton/ha respectively.

The production of clam was estim
relation noted on clam production and stocking biomass although the growth and survival
were negatively affected. Among the small stocking size group, the final production
increased accordingly with the increase stocking biomass and no significant difference
(P>0.05) was detected between T1 and T2 nor T3 and T4. However, T1&T2 were
significantly different in final production compared to T2 & T3. The percentage of biomass
gained, in contrast, was showing reduction trend when increasing the stocking biomass and
no significant difference between T1 and T4 was detected. This is due the fact that the
increase in biomass negatively affected the growth and survival of the clams.
Table 4. Biomass production of clam at stocking size of 1.0cm
Treatments T1 T2
Final production (ton/ha) 4.14±0.57
a
6.82±0.56
a
12.62±2.16

b
14.84±0.91
b

Biomass gained (ton/ha) 3.62±0.57
a
5.78±0.56
a
10.54±2.16
b
11.72±0.91
b

% of biomass gained 6 5 5 97.1±109.4
a
55.8±53.6
ab
06.9±104.0
ab
375.8±29.3
b

Value (Mean±SD) followed by differen letters with fferen
were significantly
mass production of clam at stocking size of 1.7cm
T7 T8
t superscript in a row are significantly di t (P<0.05). T1,
T2, T3 and T4 are treatments of clam cultured at 0.5, 1.0, 2.0 and 3.0 tons/ha respectively

In the bigger stocking size (1.7cm), the final production in the treatments

increased as increase in stocking biomass (p<0.05) while the biomass gained was not
significant different (p>0.05) in the treatment T5 and T6. The percentage of biomass gained,
in contrast, was reduced as increasing of stocking biomass in T5, T6 and T7. However, the
treatments T7 and T8 were not significantly different in terms biomass gained during the
experimental period. In both sizes the increase in biomass certainly impacted net production
negatively.
Table 5. Bio
Treatments T5 T6
Final production (ton/ha) 9.49±0.68
a
14.46±0.69
b
23.58±0.68
c
34.80±1.00
d
Biomass gained (ton/ha) 6.10±0.68
a
7.68±0.69
a
10.02±0.69
b
14.46±0.99
c
% of biomass gained 180.0±20.0
a
113.3±10.1
b
73.9±5.1
c

71.1±4.8
c


1
Value (Mean±SD) followe
T6, T7 and T8 are treatme
d by diffe lette are si fferen 5,
nts of clam 6.8, 6 on/ha .

ical calculation
rent superscript
cultured at 3.4,
rs within a row
13.6 and 20. t
gnificantly di
respectively
t (P<0.05). T
However, the increase in biomass gained as well as final production indicated the benefit can
be obtained if the appropriate stocking biomass was determined. The econom
therefore is necessary to optimize investment benefit.

2
1.5 Fatty acid profile
Table 8. Fatty acids of clam cultured at different stocking sizes and different stocking
biomass
Fatty Acids T1 T2 T3 T4 T5 T6 T7 T8
14:00 0.58 1.07 0.59 2.52 6.35
16:00 44.26 42.67 78.27 21.63 47.07 84.63 33.54 33.94
16:1(n-7) 9.85 3.53 7.88 0.75 10.94 11.71

17:00 0.19 0.89 1.94 1.22
17:1(n-7) 3.39 7.71
18:00 4.63 15.63 22 23.98 16.82 7.84 10.08 10.72
18:1(n-9) 63.02 39.79 26.83 29.68 49.38 33.41 27.18 31.94
18:1(n-7) 5.31 6.33
18:2(n-6)t 0.41 8.19 1.06 2.35 13.74
18:3(n-3) 0.54 1.1 5.16
20:1(n-9) 7.83 0.52 8.18
20:2(IS) 0.16 0.47 0.16 0.16 0.16 0.47 0.16 0.16
20:4(n-6) 1.11 7.72 2.98 5.06 2.72 3.54 8.9
20:4(n-3) 0.31
20:5(n-3) 4.45 3.11 5.95 6.2 0.97 7.96 3.29
24:00:00 1.17
22:5(n-6) 1.56
22:5(n-3) 3 4.96 1.85 2.46
22:6(n-3) 45.78 29 33.62 29.65 27.58 62.77 30.4 30.0
Sum (n-3) 50.23 35.11 38.58 37.76 33.78 63.74 40.82 30.29
Sum (n-6) 0.11 0 7.72 2.98 5.06 2.72 5.1 8.9
Sum HUFA 50.34 35.11 46.3 40.74 38.84 66.46 45.92 42.19
Total mg FAME/g DW 174.3 149.2 176.9 134.4 166.6 193.7 139 166.1
Value = mg/gDW; T1, T2, T3 and T4 are treatments of clam size 1.0 cm cultured at 0.5, 1.0, 2.0 and 3.0 tons/ha
respectively; T5, T6, T7 and T8 are treatments of clam size 1.7cm cultured at 3.4, 6.8, 13.6 and 20.6 ton/ha
respectively.

There was variability in the fatty acid profile between treatments independent of different
stocking biomass. However, the presence of DHA at a very high content (29.00 to
62.77mg/gDW) and sum of HUFA indicated the high nutritional value of clam. The total
FAME varies from 134.4 to 193.7 mg/gDW. The variation of fatty acids of clam may relate
to the ovary and/or growing development stage when fatty acids normally accumulated. This
result showed the quality of clam in term of fatty acids profile needs further researches.

1.6 Economical evaluation
The estimation of the economic benefit of clam cultured in the intertidal areas is showed in
the table 6 and table 7. The net profit estimated based on the output cost and input cost and
value/price of clam.

3
Table 6. Economical evaluation of clam rearing at stocking size of 1.0cm
Treatments T1 T2 T3 T4
Input
Seed cost (35.000 VND/kg) 17,500,000 35,000,000 70,000,000 105,000,000
Mesh and fencing (VND/ha) 3,300,000 3,300,000 3,300,000 3,300,000
Labour cost for protection, cleaning
(6monthsx1.200.000 VND/m) 7,200,000 7,200,000 7,200,000 7,200,000
Hut for daily monitoring (VND/hut) 5,000,000 5,000,000 5,000,000 5,000,000
Land lease (VND/ha) 4,000,000 4,000,000 4,000,000 4,000,000
Harvesting cost (2% of production
cost) 994,320 1,636,320 3,028,800 3,561,600
Total input (A) 34,994,320 53,136,320 89,528,800 125,061,600
Output
Total output (12.000VND/kg) (B) 49,716,000 81,816,000 151,440,000 178,080,000
Net profit (A - B) 11,721,680 25,679,680 58,911,200 50,018,400
% of seed investment 46.06% 62.35% 75.65% 81.99%
% of investment benefit 30.85% 45.75% 63.67% 39.06%
T1, T2, T3 and T4 are treatments of clam cultured at 0.5, 1.0, 2.0 and 3.0 tons/ha respectively. The
The main cost in clam culture is the expenditure in seed purchase. Cost of seed ranged
between 46% to 81% in small size seed (1cm) for the four treatments ( T1, T2 T3 &T4). As
all other costs are fixed the increase in stocking biomass increased the cost. Although total
production increased with the increase in stocking biomass, the economic analysis clearly
indicated that the net profit decreased beyond the level of 2 tonnes/h stocking biomass (T3).
The T4 with the stocking density of 3 tonnes/h is yielded lesser net profit compared to T3.

This can be explained by the proportion of seed cost was relatively high while the growth and
survival of this treatment was lower compared to other treatments with low stocking biomass.
Therefore the stocking biomass of 2 ton/ha should be recommended for clam culture in the
intertidal area at stocking size of 1cm height for period of 6 months.
Table 7. Economical evaluation of clam rearing at stocking size of 1.7cm
Treatments T1 T2 T3 T4
Input
Seed cost (18.000 VND/kg) 61,200,000 122,400,000 244,800,000 367,200,000
Mesh and fencing (VND/ha) 3,300,000 3,300,000 3,300,000 3,300,000
Labour cost for protection, cleaning
(6monthsx1.200.000 VND/m) 7,200,000 7,200,000 7,200,000 7,200,000
Hut for daily monitoring (VND/hut) 5,000,000 5,000,000 5,000,000 5,000,000
Land lease (VND/ha) 4,000,000 4,000,000 4,000,000 4,000,000
Harvesting cost (2% of production
cost) 2,278,080 3,470,400 5,659,200 8,352,000
Total input (A) 79,978,080 142,370,400 266,959,200 392,052,000
Output
Total output (12.000 VND/kg) (B) 113,904,000 173,520,000 282,960,000 417,600,000
Net profit (A - B) 30,925,920 28,149,600 13,000,800 22,548,000
% of seed investment 73.75% 84.20% 90.68% 92.95%

4
% of investment benefit 37.27% 19.36% 4.82% 5.71%
T5, T6, T7 and T8 are treatments of clam cultured at 3.4, 6.8, 13.6 and 20.6 ton/ha respectively.
In the bigger size group with higher stocking biomass the net profit continue to reduce net
profit as seed cost increased up to 93%. The price of seed was much higher than that of
harvested clam, the net profit therefore relatively low compared to smaller size seed stocking
treatments. It is therefore recommended that the stocking biomass should not be higher than
6.8 ton/ha.
5.1.1.2. Trial on rotational culture of clam

Prawn farming in Central Vietnam normally occurs in April to September each year; the
rotation clam culture has to wait until September. Clam rotational culture is possible in
prawn farms between October and March. The aim of this trial is to evaluate the feasibility of
an alternative clam crop in prawn farms during October to March. The objective of the
experiment was to determine appropriate size for the short-term culture. Clams must reach
marketable size within the period available before the start of prawn culture season.
Materials and method
The experiment was conducted in prawn ponds of 50m
2
using 3 replicates in two treatment
with a stocking biomass of 3.39 ton/ha ( T1) and 9.83 ton/ha (T2). In this trial, clam size of
1.9 cm height was stocked at stocking biomass of 3.39 ton/ha and the clam size 2.6cm height
was stocked at stocking biomass of 9.83 ton/ha. Those larger stocking sizes were selected
due to the culture duration in the pond were limited as a rotational crop with main crop,
prawn, it was necessary to ensure the clam reaching market size within relatively shorter
culture duration. This experiment was terminated after 165 days rearing. The sandy bottom
was provided as this substratum was found most suitable from previous experiments.
Water quality parameters such as temp, DO, pH, turbidity, salinity were being monitored
daily. The nutrient such as total N, ammonia NH3, nitrate NO3 and total phosphorous was
monitored weekly.
Growth of clam, expressed in mean of height (cm) and mean of weight (gr), was determined
by random sampling (n=30) and measure every forthnight. The daily specific growth rate
(SGR, weight basic) was calculated using the following formula:
SGR(%/day) = 100*(LnW
f
-LnW
i
)/t
Where: W
i

and W
f
are mean of initial weight and final weight, respectively and t is number
of experiment days.
The final production (expressed as ton/ha) of each treatment was conducted by entirely
harvested and the biomass gained was calculated from final production minus the stocking
biomass.
Size variation was evaluated according to (Wang et al., 1998) in which the mean of three
replicates of the coefficient of variation (CV) was used to examine the inter-individual
weight variation among the clam in each treatment: CV(%)=100*SD/ M where M is mean of
weight and SD is standard deviation of the clam in each treatment.
The meat ratio (% of meat weight/ total weight) of clam in this experiment was evaluated to
determine meat yield. The total weight and the weight of meat (separating the meat from the
shell) measured from the randomly selected samples.
All data of the treatments were tested for significant differences (p<0.05 or p<0.01) using
One-way ANOVA followed by Turky test for multiple comparisons of means. The data are

5
expressed as Average and statistical analysis was performed using GraphPad Prism version
4.0 and Microsoft Office EXCEL for Window.

Results:
Environment conditions of the trial ponds
Table 9. The environment conditions in ponds
pH DO (ppm)
Temperature (
o
C)
Salinity (ppt) Turbidity (cm)
T1 (1.9 cm)

Mean
6.29 20.73 21.17 49.35
Max
8.47 8.56 30.73 29.00 60.00
Min
7.45 3.88 14.70 10.00 38.00
T2 (2.6)
Mean
±SD
6.31 20.84 21.18 48.92
Max
8.70 8.40 30.73 29.00 60.00
Min
7.46 4.75 16.23 10.00 45.00
The environment conditions in the trial ponds fluctuated widely. The temperature ranged
between 14.7 to 20.8
o
C but still was acceptable for clam growing. The salinity ranged
between 10 to 21.2ppt. The experiment started during rainy and low temperature climate and
ended in summer season. This change in climate has reflected in the environmental
conditions in particular pond water temperature and salinity. The environmental data clearly
indicated that both treatments were experienced similar environmental conditions.
Table 10. Nutrients level in the trial ponds
Treatments P total NO3 NH3
T1 0.196±1.34 2.353±0.697 0.006±0.006
T2 0.185±0.120 2.267±0.754 0.006±0.006
The details of nutrients levels (phosphorus, nitrate and ammonia) are provided in the table
10. The nutrient levels did not vary significantly between treatments. The different levels of
biomass did not impact ammonia levels in the pond. Clam is a filer feeding organism mainly
consuming algae- in this case the clam consumed naturally occurring algae in the pond.

Unlike fish or prawn culture no supplementary feed was used based on the stocking biomass
which could have made the difference in the ammonia level in the ponds of the two
treatments.
Survival and grow performance of the clam
Table 11. Survival and growth performance of clam in the rotational pond cultures
Stocking size\Parameters Size 1.9 cm Size 2.6 cm

6
Survival (%) 78.49±4.33
a
75.98±6.33
a
SGR 0.241±0.029
a
0.161±0.020
b
Final length (cm) 2.26±0.09
a
2.81±0.10
b
Final weight (g) 8.72±0.10
a
15.56±1.66
b
Meat ratio (%) 11.35±0.98
a
12.45±1.28
b
CV% (weight) 15.99±2.38
a

20.56±3.40
a
Value (Mean±SD) followed by different superscript letters within a row are significantly different (P<0.05)
Survival of clam at different stocking size and different stocking biomass in ponds were not
significant different (p>0.05). The SGR of small size was higher than the big one though the
size variation was not significant different (table 11). This result suggested that clam cultured
in ponds might not be limited by the stocking biomass of 9.83 ton/ha under the
environmental conditions tested in this trial.
Clam quality
The meat ratio (table 11) as well as the total fatty acids (table 12) of clam size 2.6cm was
higher than that of the clam size 1.9cm can be explained by the accumulation of nutrition for
gonad development of the clam at bigger size although they were stocked at higher biomass
(nearly three times higher). This also indicates the feed availability in ponds was not the
factor that limited the clam quality. The presence of the number of fatty acids detected in this
clam compared to those in the clam cultured in the intertidal area indicated that clam cultured
in pond were not different in terms of quality as food for human consumption
Table 12. Fatty acids of clam cultured at different stocking sizes and different stocking
biomass in the rotational ponds
Fatty Acids Clam at stocking size of
T1:1.9cm (3.39 ton/ha)
Clam at stocking size of
T2: 2.6cm (9.83 ton/ha)
14:00
0.88 1.81
15:00
1.67 1.19
16:00
80.88 96.07
16:1(n-7)
3.03 3.80

17:00
2.60 1.60
17:1(n-7)
8.12 3.61
18:00
13.79 12.25
18:1(n-9)
7.82 9.90
18:2(n-6)
0.60 0.82
18:3(n-3)
1.77 0.64
20:1(n-9)
0.23 0.29
20:1(n-7)
0.68 0.51
20:2(IS)
0.47 0.47
20:4(n-6)
3.70 4.26
20:5(n-3)
3.91 3.84
24:00:00
0.98

7
22:5(n-3)
0.65 0.44
22:6(n-3)
25.61 27.56

Sum (n-3)
29.73 31.54
Sum (n-6)
3.70 4.77
Sum HUFA
33.77 35.80
Total mg FAME/g DW
160.73 166.52
Value = mg/gDW
Production and economical evaluation
Table 13. The production of clam in the rotational pond cultures
Stocking size\Parameters T1 (Size 1.9 cm) T2 (Size 2.6 cm)
Stocking biomass (ton/ha) 3.39 9.83
Final Production (ton/ha) 5.34±0.30 13.31±0.52
Final Biomass Gained (ton/ha) 1.95±0.03 3.48±0.52
% of biomass gained 57.56±8.70 35.4±5.21
Net profit (*1000 VND) )
(1)
23.4 41.8
% of investment profit
57.55% 35.40%
Value (Mean±SD).
(1)
Calculated base on seed cost with assumption the seed and the clam harvested are same
price.
The production of clam was much higher at high stocking biomass treatment. However, since
the small size and low stocking biomass resulted in better growth, the biomass gained of the
clam size 2.6cm was lower than that of the clam size 1.9cm. Moreover, due to clam were
stocked at different size and different biomass, it is impossible to understand the growth and
survival whether have been affected by the stocking size or by the stocking biomass. The

comparison of the two treatments indicated that the bigger size of clam stocked at higher
biomass resulted in better net profit but lower in the rate of investment profit (table 13).
5.1.2

Hatchery production
The previous six month period was focussed on establishing the infrastructure facilities and
live feed (microalgae) production facility for the hatchery spat production trials. In this report
the experiments on brood-stock conditioning and larval rearing are included.
5.1.2.1 Brood-stock conditioning experiment: effect of sandy bottom on gonad
development
This experiment was designed to compare the effect of substrata on gonad development of
clam under stable water temperature condition.
Materials and method
The broodstocks were collected from tidal areas of Thanh Hoa province and were transferred
to ARSINC’ hatchery for the experiment. The average size (height, mm) expressed as
Mean±SD of breeders were 33.27±5.27 mm equipvalent to 26.38±8.23g per individual

8
The experiment was conducted in 6 cylindro tanks volume of 200L each and tanks for
treatments were randomly allocated. Two treatments (three replicates each) including sandy
botom versus non-sandy bottom were tested. All the tanks were conducted in a recirculation
system equipped with temperature control equipment to maintain water temperature
constantly at 26
0
C (±0.5
o
C). DO and pH were maintained at 6.27±0.32 and 7.8-8.3
respectively. Clam were allocated at the same density of 145 individuals per tank. Clam were
daily fed a mixtured of microalgae Nonochloropsis sp and Chaetoceros sp at ratio of 1.5:1.5
billions cells per clam per day. The feeding frequency was adjusted at 6 times per day (6h,

9h, 12h, 15h, 18h and 21h). Every 5 days, 10 clam of each tank were randomly sampled for
gonad development inspection. The gonad index was calculated from gonad wet
weight × 100/body wet weight (without shell). The experiment was terminated after 25 days
rearing.
All data of the treatments were tested for significant differences (p<0.05) using T-test for
unpaired comparisons of means. The data are expressed as Average±SEM and statistical
analyzed was performed using GraphPad Prism version 4.0 and Microsoft Office EXCEL for
Window.
Results and disscussion
2.1. Survival of breeders
Results from data analysis (t-test) showed that the mortality of brooder clam was not
significantly different (p>0.05) in difference of substrata (Fig 2). Average of survival of the
sandy bottom and without sandy bottom was 87.4± 4.4 and 80.9± 4.0 respectively.
Sandy No sandy
0.7
0.8
0.9
1.0
a
a
Treatments
Survival (%)

Fig 2. Survival of clam conditioning at different substrata

The total weight and ratio of meat/total weight (wet weight basic) of clam was stable during
cultivation (table 14).
The maturation rates of clam in this experiment are presented in the fig 3. During the first 10
days, the maturation rate of both treatments was steadily decreased. During next 10 days, the
non-sandy bottom remained MR below 30% while the sandy bottom resulted in dramatically

increase (up to 57% at day 20). In the last 5 days, it was slightly decrease in both treatments.

9
2.2. Gonad development
Table14. Development of clam conditioning on different substrata (Mean±SD)

Total weight (g) Meat/ weight ratio Maturation rate
Sandy bottom
Day 0
26.38±8.23 15.01±2.08 0.43±0.25
Day 5
28.98
±6.79 13.08±1.83 0.37±0.21
Day 10
28.32
±8.24 13.08±2.53 0.23±0.15
Day 15
30.30
±7.93 11.71±1.55 0.47±0.15
Day 20
28.82
±6.95 12.48±1.79 0.57±0.06
Day 25
29.21
±7.68 12.44±1.92 0.47±0.15
Non-sandy bottom
Day 0
26.38±8.23 15.01±2.08 0.43±0.25
Day 5
29.87

±7.06 14.08±1.73 0.13±0.06
Day 10
27.96
±5.97 12.81±2.01 0.27±0.12
Day 15
27.30
±5.87 12.50±1.89 0.27±0.23
Day 20
27.88
±4.99 12.79±1.27 0.30±0.10
Day 25
26.87
±5.62 13.06±1.91 0.23±0.06

0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
Day 0 Day 5 Day 10 Day 15 Day 20 Day 25
Age (days)
Maturation rate
Sandy
Non-sandy

Fig 3. Comparison of maturation rate of clam at different substrata (Mean±SD)

The maturation rate in this experiment indicated that clam can mature better with sandy
bottom in the controlled conditioning system. The result clearly supported the theory of
appropriate sandy substrata for clam development. The relatively higher maturation rate on
the day 0 indicates that the clams collected are in reasonable mature state. However, the clam
took initial period of 10 days to respond positively in the environmental and food availability
in the controlled conditioning systems provided in this experiment. Brooders required about
10 days for adaptation under new conditions. This adaptation period could be attributed to
the decrease in the maturation rate. Within next 10 days more than 50% clams matured and
ready for spawning. To clarify those matters in particular boorder adaptation or
acclimatisation period, more research should be addressed.
Details different stages of gonadial development are presented in plat 1.

10

Gonad Sta
g
e 1 Gonad Sta
g
e 2

g
e 3 Matured
g
ona
d

Gonad Sta

Plate 1: showing gonadial stages from the conditioning experiment

11
5.1.2.2 Clam larval rearing experiments
The experiments on larval rearing and nursing still under way. Due to the flooding in coastal
areas of North central region and some damage in the hatchery, affected by the storm Lekima
on Aug, the experiments on larval rearing have to delay as lack of matured breeders and
shortage of algae production.
5.1.2.3 Spat production
Besides implementing experiments for larval rearing, 3 batches of clam larvae were
conducted in the big tank volume (3m
3
each). The culture protocol was modified from
experiments on larval rearing conducted last year. The first two batches encounter problem of
contamination due to malfunctioning of filtration system in water treatment section. For the
experience and valuable information gained those trials, the new trial was conducted in very
strict conditions resulted in production of around 2 million spat. At the moment, attempt is
made by the hatchery team to produce 6.5 million of spa to meet the target before Apr, 2008.
Following revised methods followed to produce 2 million spats based on the previous
experimental results.
A. Brood stock conditioning
- Clam brooders were transferred from the culture areas in Thanh Hoa Province to the
hatchery. The maturity stages of gonad of the brooders were checked (at II stage).
The brooders were stocked in constant water temperature condition (at 25
0
C) in
recirculation system for 20 days for further maturation of gonads. The gnads attained
maturation during this period and ready for spawning.
- The brooders were fed with algae estimated about 3 billions of cells/ml per clam per
day consists of Chaetoceros sp, Nanochloropsis sp. Feeding frequency was 4 times

in 24 hours (6h, 11h, 16h, 21h).
- The salinity was maintained at 25ppt during conditioning period, the bottoms of tanks
were provided with sandy substrate.

B. Spawning method
- The matured brooders were transferred to spawning tank for the spawning. The male
and female were kept together in the same spawning tank (200 lit) with density at 150
clams per 200 litter tanks.
- The brooders were exposed to combination of shock treatments by sudden reduction
of temperature (4
0
C) and gentle stimulation (opening some matured clams and
removing its gonad out then crushing and mixing with water in the spawning tank).

C. Larval rearing procedure
- 3 hours after the spawning of clam, the embryos were transferred to incubation tank,
stocked at 15/ml. After 24 hours, larvae at D veliger stage were sieved through a
45µm screen, and then pooled into a culture tank. Larvae stocked at 7/ml.
- Water exchanged of 100% every 2 days culture, using wet screen for washing larvae.
Screen size was increased at each water change, the screen mesh selected depending
on the growth of larvae:

Larval size (µm) Mesh size (µm)
45 20
60 45
80 45

12
100 60
130 80

160 100
200 150
230 180

- Feed ration of mixed of 3 algae species (Isochrysis sp, Nanochloropsis sp,
Chaetoceros sp) maintained at 100.000 cells/ml.
- Larvae were measured every morning, and total larval numbers were estimated every
2 days after exchanging water and cleaning tank.
- Water salinity for larvae reared was maintained at 25ppt.

D. Spat collection method
- Larvae were at swimming stage for initial 8 days culture and after that they became
metamorphosis stage, ready for settlement.
- Larvae are pooled into 150µm screens with artificial substrata on bottom (up welling
system).

E. Nursery cycle
- Post setting larvae was provided nursery system by using an upwelling condition,
including 10 hanging screens on a surface of a 2 cubic meters rectangle tank. Water
with algae provided by flow through by using a pump from bottom to each screen for
feeding larvae.
- Stocking density of larvae at 200.000 per a cylinder screen (45cm diameters, 30cm
height)
- Feed ration of mixed of 3 algae species above maintained at 150.000 cells/ml.
- Water exchanged of 50% every day and 100% every 2 days, during this time, larvae
were also cleaned by water tap.
- Water salinity for nursery was maintained at 25ppt.

The details of larval development including settlement is presented in plat 1&2

13
















Embryonic stage

Umbo larval stage





D larval stage





Plate 2 showing clam larval developmental stages








14

Larval settling stage















Post settling stage

Spat





Plat 3 showing larval settlement and spat formation

15

5.1.3

Propagation of the technologies (on farm trials level)
In Aug, 2007 an introduction workshop had been successfully organized in Cua Lo, Nghe An
province. The objectives of the workshop were to introduce the primary results of the project
on clam hatchery and clam husbandry work and discuss the plan for developing collaboration
for onfarm trials (appendix). The invited participants including leaders of RIA1, leaders and
technicians of the National Fisheries Extention Center and Provincian Fisheries Extention
Center of 6 provinces and innovative farmers who were interested in clam culture. At the
workshop, a lot of suggestion, comments as well as expression of interest on the clam culture
technology have been recorded. The aquaculture technicians and farmers also expressed their
concerns about the clam culture in brackish water ponds, polyculture with prawn and
requested more research information.
5.2 Smallholder Benefits
5.2.1 Opportunity to utilize the brackish water ponds for clam production
The success that clam can survival and growth in pond opens opportunity for farmers to

utilize the brackish water ponds where the shrimp industry recently has been collapsed due to
bad management. In addition, success of clam culture as alternative crop will provide new
opportunity for the farmers to utilise the prawn farm which normally used only 4 months per
year for shrimp culture and thus provide more livelihood for the communities in the North
Central coast.
5.2.2 Increasing in production and benefit from clam culture in the intertidal areas
The success of intertidal trials provides data base and practical knowledge to build a
technical guideline for clam grow out. Appropriate stocking density and stocking size will
provide higher productivity, reduce the operation cost and bring in higher benefit.
5.2.3 Easily Applicable Farming Knowledge
Factors such as stocking density and salinity are within the capabilities of smallholder end-
users to monitor and manipulate. By focusing upon the research and understanding of the
impact of such factors on survival and growth of M lyrata and its larvae, the teams at
ARSINC are building the knowledge base for farming practices that can be applied by
smallholders.
5.2.4 Low Investment Risk
The focus on low-cost, reliable production and hatchery techniques and infrastructure
provide for low investment risk to the smallholder and smallholder communities.
5.2.5 Maximizing Commercial Potential through Knowledge
The following table summarizes the implications of the knowledge generated by this project
for the smallholder’s commercial production potential

Table . Technology Implications for M lyrata Commercial Production
Farming
Component
Knowledge Implications for Commercial Production
Production Density
• Farmers need to know optimum stocking density
that provide for maximum productivity per m
2

16