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

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 province

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

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

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

Leader, Integrated Biosystems Integrated Resource Management and Biotechnology

Organisation South Australian Research and

Development Institution (SARDI)

Name: Nhu Van Can Telephone: +84.383829884

Position: Director Fax: +84.383829378

Organisation Aquaculture Research Institute for

North-Central

Email: arsinc@vnn.vn

• 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

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

• 1st

six monthly report

• 2nd

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 4th 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

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

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 m2 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*(LnWf-LnWi)/t Where: Wi and Wf 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 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, -196oC) 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±2.40oC s

Table 1 Environment conditions in the cultured areas

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

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

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

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

1.4 Production and quality

ated from both growth and survival There was a positive

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

Final production (ton/ha) 4.14±0.57a 6.82±0.56a 12.62±2.16b 14.84±0.91b

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

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

Final production (ton/ha) 9.49±0.68a 14.46±0.69b 23.58±0.68c 34.80±1.00d

Biomass gained (ton/ha) 6.10±0.68a 7.68±0.69a 10.02±0.69b 14.46±0.99c

% of biomass gained 180.0±20.0a 113.3±10.1b 73.9±5.1c 71.1±4.8c

Value (Mean±SD) followe

T6, T7 and T8 are treatme

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

1.5 Fatty acid profile

Table 8 Fatty acids of clam cultured at different stocking sizes and different stocking

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

Table 6 Economical evaluation of clam rearing at stocking size of 1.0cm

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

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

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

% 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 50m2 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*(LnWf-LnWi)/t Where: Wi and Wf 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

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 (oC) Salinity (ppt) Turbidity (cm)

The environment conditions in the trial ponds fluctuated widely The temperature ranged

between 14.7 to 20.8oC 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

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

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

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)

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

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 260C (±0.5oC) 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

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