Collaboration for Agriculture & Rural Development: Technical and economic feasibility of applying the Better Management Practices (BMP) to household aquaculture in Vietnam - MS 8 " doc

The report proceeds with a methodology Section 2, an analysis of environmental quality parameters of shrimp aquaculture systems including the potential impact of shrimp production on foo

Ministry of Agriculture and Rural Development

COLLABORATION FOR AGRICULTURE AND RURAL DEVELOPMENT (CARD)

Environmental and Economic Evaluation of Better

Management Practices for Shrimp Culture in Vietnam

Nguyen Xuan Suc1, Dinh Van Thanh1, Bui Kien Cuong1,

Virginia Mosk2 and Elizabeth Petersen2

1 Research Institute for Aquaculture No 1 (RIA1), Tu Son, Bac Ninh

2 The University of Western Australia, 35 Stirling Hwy, NEDLANDS WA 6907

§ Corresponding Author: Liz.Petersen@tpg.com.au, Ph/Fax: +61 8 9332 8310

- 2008 -

Environmental and Economic Evaluation of Shrimp Culture Practices in Vietnam

Research Institute for Aquaculture No 1 & The University of West Australia 2

Acknowledgements

The authors would like to sincerely thank the Collaboration for Agriculture and Rural Development (CARD) Programme for funding this research We would also like to thank the following institutions for their support:

• The Research Institute for Aquaculture Number 1 in Vietnam,

• The University of Western Australia,

• The Center for Fisheries Extension in Ha Tinh, Nghe An, and Thua Thien-Hue,

• Vietnam’s National Fisheries Quality Assurance and Veterinary Directorate (NAVIQAVED), and

• The nine farming households for participating in the trial:

o Phan Ngan,

o Hau Van Anh,

o Tran Dinh Van,

o Cao Xuan Hoa,

o Le Van Tuan,

o Dinh Van Dung,

o Nguyen Hong Quyen,

o Nguyen Ngoc Hanh, and

o Hoang Xuan Kien

Executive Summary

The aim of the report is to provide an initial investigation into whether Better Management Practices (BMPs) can be adopted by Vietnamese shrimp farmers to reduce the environmental and food safety risks of shrimp production, while ensuring the farms remain economically viable It includes analysis of data from in-field measurements and laboratory analysis of key environmental quality parameters at different locations within shrimp farming systems that implemented BMPs, including water in inlet canals before it enters cultivation ponds, water within the cultivation ponds themselves, and water in outlet canals once it has exited the pond The same in-field measurements and laboratory analysis is conducted for shrimp ponds of nine farming households implementing BMPs (three each in Nghe An, Ha Tinh and Thua Thien-Hue) Chemical and microbial analysis is also conducted on shrimp produced in these nine households, and the economic viability of their operations is assessed

While trials need to be conducted on a larger number of farms over a longer time period for the findings to be presented with confidence, initial results in this report suggest that implementation of BMPs are generally effective at controlling environmental water quality, and chemical and microbial outbreaks Moreover, the profitability of farms using these practices are just as cost-effective as farms that do not use BMPs (the benefit cost ratio of BMP and non-BMP farms are similar) Hence, widespread adoption of these practices in Vietnam is not likely to have a detrimental impact on profitability of farming enterprises Rather, it is likely to have a positive impact if export markets can be ensured or possibly expanded with product certification

Specific key findings

1 Analysis of environmental water sampling showed that, on average, a number of parameters were within recommended limits for maximising shrimp production, including: salinity and water temperature (although significant variation outside recommended limits was reported through time for these two parameters), pH, ammonia, alkalinity, nitrogen dioxide and hydrogen sulphide,

2 Transparency readings were found to be slightly problematic being mostly above the optimal range which showed a difficulty in establishing good phytoplankton blooms Temperature was sometimes found to be lower than recommended levels for optimal production,

3 The one problematic environmental parameter was dissolved oxygen – with levels being consistently below recommended levels for maximised production, especially in the morning Moreover, low dissolved oxygen levels in output channels have the potential to be hazardous to significant varieties of fish fauna Pond aeration prior to discharge is likely to negate these impacts, although the cost impacts

to the shrimp enterprise needs to be assessed,

4 Chemical and microbial analysis found no or negligible levels of chemicals or microbes harmful to shrimp (for production or food

Environmental and Economic Evaluation of Shrimp Culture Practices in Vietnam

Research Institute for Aquaculture No 1 & The University of West Australia 4

5 Total costs of half-hectare shrimp operations is approximately 55 million VND (approximately USD3,400 at the time of writing) These costs are dominated by feeding (51%) There is significant variation in costs across farms,

6 The average production is just over 1 tonne/half-hectare operation, valued at 76 million VND (approximately USD4,700 at the time of writing) This is also very variable across shrimp operations,

7 The average price received for the shrimp was 73,000VND per shrimp, although higher prices were received for larger shrimp compared with the small shrimp (by weight),

8 Profit was approximately 21 million VND (approximately USD1,300 at the time of writing), compared with 8 million VND for non-BMP farmers The average Benefit Cost Ratio was approximately 1.3, on par with non-BMP farmers This suggests that the study farms invested significantly more funds into their operations, than the average non-BMP farmer,

9 If environmental water quality is contained within recommended limits, and chemical and microbial outbreaks are avoided, then the major determinant of profit was feeding The most cost-effective farms were those that invested heavily in feeding the shrimp

10 There are significant opportunities for increased capitalisation of shrimp enterprises Significant growth in Vietnam’s shrimp aquaculture industry has the potential to be sustained in the medium-term

Table of Contents

Acknowledgements 2

Executive Summary 3

1 Introduction 6

2 Methodology 8

3 Environmental Quality of Shrimp Aquaculture Systems 10

3.1 Transparency 10

3.2 Salinity 11

3.3 pH 12

3.4 Dissolved oxygen (DO) 12

3.5 Water temperature 13

3.6 Ammonia (NH3) 14

3.7 Alkalinity 15

3.8 Nitrite 15

3.9 Sulphides 16

3.10 Key findings 17

4 Household Shrimp Production 18

4.1 General information on household operations 18

4.2 Environmental water quality data 19

4.3 Shrimp produt quality analysis (chemical and microbial) 22

4.4 Costs of production 23

4.5 Production volume and value 27

4.6 Profit and Benefit Cost Ratio 29

5 Discussion and Conclusions 31

5.1 Environmental water quality parameters 31

5.2 Shrimp production and profitability 32

5.3 Summary comments 33

Bibliography 34

Appendix 1: Better Management Practices 35

Environmental and Economic Evaluation of Shrimp Culture Practices in Vietnam

Research Institute for Aquaculture No 1 & The University of West Australia 6

1 Introduction

Household shrimp production is the predominant form of coastal aquaculture in Vietnam In 2006, approximately 459,000 tonnes of shrimp was produced comprising 12% of total fisheries production in Vietnam (USDAFAS 2007) Approximately 34% of shrimp production (158,000 tonnes) was exported at a value of USD1.46billion Shrimp production is increasing, with an average of 13% growth experienced each year from 2000 to 2006 (USDAFAS 2007) Prices have remained steady such that the growth in the value of shrimp production is similar to the growth in volume

Approximately 70% of shrimp production (by volume) is produced through aquaculture operations, which comprises approximately 24% of total aquaculture production by volume but 71% by value (Fistenet 2007) Aquaculture production of shrimp experienced an average of 26% growth between 2001 and 2006, compared with 2% growth in the wild-caught sector

In recent years, residues and contaminants have been detected in exported shrimp, with devastating results in markets In 2003, five consignments from Thua Thien-Hue (TT-Hue) province to the European Union were destroyed or returned because of the presence of residues, and a far larger quantity from all north central provinces were similarly treated in 2004 Low standards of education, limited farm capital and minimal opportunities for capacity-building amongst households have resulted in inappropriate farm practices, which have caused degradation of the environment, declines in water quality, loss of farm resources and disease outbreaks As a consequence, the livelihood of many of these farmers is threatened

The loss of production, negative environmental and socio-economic impacts, and food safety concerns have provided impetus for the development and extension of better management practises (BMP) for household shrimp farms BMPs have been used in many countries to implement the more general principles of responsible shrimp farming (FAO 2005) They can be defined as farm and local-level practices aimed at enhancing efficiency, productivity, mitigating negative environmental and socio-economic impacts, and suppling products that meet requirements of food safety BMPs are voluntary and are becoming widely used as an important strategy to enhance the marketability of aquaculture product

A number of projects have contributed to the development of practical BMPs for shrimp farming in Vietnam (e.g a DANIDA-funded (Danish International Development Agency) SUMA/NACA project (Support to Brackish Water and Marine Aquaculture/Network of Aquaculture Centre in Asia-Pacific), and a NAFIQAVED (National Fisheries Quality Assurance and Veterinary Directorate) pilot project - see Appendix 1 for the list of BMP protocols) These projects have proposed specific BMPs and have conducted some small-scale testing of these BMPs Their findings have not yet been widely disseminated among producers and BMP implementation is still limited This is due to a number of financial, social, technical and economic feasibility constraints Small-scale household shrimp farms are extremely diverse and fragmented, and their capacities to adopt BMP are hampered by lack of awareness, capital constraints and lack of perceived incentive The benefits of applying BMP to

household farms remain to be fully investigated However, experience in Thailand, India and Bangladesh has shown that small-scale farmers who applied BMPs made gains in efficiency, productivity and quality (SUMA, 2004)

This report is one output of a project jointly funded by the Australian Agency for International Development (AusAID) and the Vietnam Ministry of Agriculture and Rural Development (MARD) through the Collaboration for Agriculture and Rural

Development Programme (CARD) The aim of the report is to provide an initial

investigation into whether BMPs can be adopted by Vietnamese shrimp farmers to reduce the environmental and food safety risks of shrimp production, while ensuring the farms remain economically viable It presents the results of environmental and

economic evaluation of BMP trials in three provinces of Vietnam (Ha Tinh, TT-Hue and Nghe An) The evaluation includes analysis of water quality as it enters and leaves shrimp ponds, product quality data, and economic assessment of household incomes for those participating in the BMP trials

The report proceeds with a methodology (Section 2), an analysis of environmental quality parameters of shrimp aquaculture systems (including the potential impact of shrimp production on food safety and the environment) (Section 3), and an analysis

of household shrimp production (including food safety, production and profitability aspects of households implementing BMPs) (Section 4) The report finishes with a discussion and conclusion regarding the initial assessment of the cost-effectiveness of BMP adoption in reducing environmental and food safety risks (Section 5)

Environmental and Economic Evaluation of Shrimp Culture Practices in Vietnam

Research Institute for Aquaculture No 1 & The University of West Australia 8

2 Methodology

Data collection was conducted over a five month period, March to July 2007, in three provinces; Ha Tinh, Nghe An, and Thua Thien-Hue (TT-Hue) (see Figure 1)

Figure 1: Vietnamese provincial map indicating the location of the three project provinces

Data was collected by three sources:

1 Extension officers These data include in-field measurements and laboratory

analysis of key environmental quality parameters at different locations within the project site Data is presented for inlets (water in inlet canals before it enters the ponds), outlets (water in outlet canals once it has exited the pond),

and within the ponds themselves Readers are referred to Ha and Suc (2007)

for more information on project sampling sites

2 Farmer households These data include in-field measurements of key

environmental quality, production and economic parameters collected by nine different shrimp farmers within the project site

3 NAVIQAVED officers (Vietnam’s National Fisheries Quality Assurance and

Veterinary Directorate) NAVIQAVED controls food safety and veterinary

services for seafood products in Vietnam They provide chemical and microbiological analyses of shrimp produced by the nine farmer households during the trial period

In-field measurements included:

• pH: measured with a portable pH meter (YSI 52)

• Salinity: use of refractometer (Spec T2000)

• Dissolved Oxygen (DO): measured with an oxygen meter (YSI 52)

• Temperature (oC): measured with a digital thermometer (Thermo 100)

• Transparency (cm): measured with Secchi disk

The running river water was used as a supply source for in-field laboratory analysis Samples were collected using a peristaltic pump with two heads, were kept cool with ice, and then analyzed immediately upon reaching the laboratory All analysis followed standard methods (Alpha 1998), and included:

The Vietnamese and Australian partners (Research Institute for Aquaculture No.1 and the University of Western Australia) collaborated in the data analysis and report writing Three Vietnamese project partners visited Perth in December 2007 to collaborate with the Australian project partners to conduct initial data analysis, discussion and planning The analysis and report was finalised through email contact

Project team

The Vietnam-based project team comprised:

¾ Mr Nguyen Xuan Suc, Project Leader,

¾ Dr Dinh Van Thanh, and

¾ Mr Bui Kien Cuong

The Australian-based project team comprised:

¾ Dr Elizabeth Petersen – Adjunct Senior Lecturer, the University of Western Australia, and Applied Economist, Advanced Choice Economics Pty Ltd,

¾ Ms Virginia Mosk, MSc – Technical Aquaculture Consultant to The University of Western Australia, and

¾ Associate Professor Steven Schilizzi – The University of Western Australia

3.1 Transparency

It is recommended that transparency (Secchi disc visibility) remain between 25 and 40cm for maximum production (Boyd 1990) If transparency is less than 25cm and the pond is too turbid with phytoplankton, this may create problems with dissolved oxygen If the reading is greater than 40cm then the phytoplankton is too scarce

Transparency readings were found to be above the maximum level at the start of the production period in ponds of all three provinces, decreasing to within recommended levels half way through the season in Ha Tinh and Nghe An (Figure 2) While transparency readings were higher than recommended in the inlets and outlets of all provinces (with the exception of the outlets in TT-Hue), transparency is considered to

be an indication of pond condition and phytoplankton density, and is therefore less important in the inlet and outlet channels

Transparency levels in the inlet and outlet are unlikely to have an impact on the environment, or affect food safety, as it is purely an optimal range for the best growth of the shrimp Plankton blooms favour greater shrimp production by stimulating the growth of shrimp food organisms and it also limits the visibility of the shrimp from predatory birds, thus reducing stress to the target species allowing them

to roam and feed, and develop more quickly

Hue - Transparency

20 30 40 50 60 70 80

Inlet Outlet Ponds

Figure 2: Transparency levels in inlets, outlets and ponds

3.2 Salinity

There is very little difference in salinity levels between water sources in any provinces (Figure 3) It is recommended that for maximum production, salinity levels remain between 15 and 25%o (Boyd 1990) Salinity levels remained between this range in Nghe An, but increased to 27%o by the end of the cultivation period in Ha Tinh, and dropped below this range mid-season in TT-Hue due to heavy rainfall which

is common for that time of year Salinity levels in the inlet and outlet during and at the end of the trial is unlikely to have an impact on the environment or food safety

Ha and Suc (2007) indicates a range of 13-24%o for the three areas prior to stocking

Hue - Salinity

11 16 21 26

Outlet Ponds

Figure 3: Salinity levels in inlets, outlets and ponds

Environmental and Economic Evaluation of Shrimp Culture Practices in Vietnam

Research Institute for Aquaculture No 1 & The University of West Australia 12

3.3 pH

It is recommended that for maximum shrimp production, pH remain between 7.5 and 8.5 (Boyd 1990) The pH of the culture pond was consistently within this range throughout the season in all provinces (Figure 4) pH levels were lower than recommended in inlets and outlets in Nghe An and in the inlets in Ha Tinh, although this does not have an impact on shrimp production if pH levels are correct within the ponds themselves

pH levels in inlet and outlet canals during and at the end of the trial is unlikely to have an impact on the environment or food safety The MS-3 baseline data report (Ha and Suc 2007) indicates a range of 6-8.30 for the three areas prior to stocking

Hue - pH

5.5 6 6.5 7 7.5 8 8.5

Inlet Outlet Ponds

Figure 4: pH levels in inlets, outlets and ponds

3.4 Dissolved oxygen (DO)

Generally, dissolved oxygen levels are highest in the inlets, and lowest in the outlets (Figure 5) Dissolved oxygen of the culture pond at Ha Tinh and TT-Hue sat above 5.5 mg/l (above 5 mg/l being optimal) even though the outlet pond readings did drop below 4.5 mg/l At Nghe An, dissolved oxygen dropped below 5mg/l for most of the season and ended at around 3.75 mg/l Despite the dissolved oxygen of the outlet pond in Ha Tinh dropping to around 2.75 mg/l at the end of the season, the culture pond stayed at a stable 5.5 mg/l As shrimp spend most of their time on the pond bottom, the mud/water interface and its oxygen content is very important Almost all muds are devoid of oxygen below a depth of a few centimetres because of poor water circulation and microbial activity within the mud Maintenance of oxygenated conditions at the mud surface is particularly important in shrimp ponds as oxygen is needed for shrimp and food organism respiration, it promotes microbial degradation

of organic matter, and prevents the release of toxic, reduced substances such as hydrogen sulphide and nitrite (Boyd 1990) If the readings where taken at the same position each time in the culture ponds it may be that there were other stagnant areas of the pond, which were not aerated and circulated properly, hence causing an overall reduction of oxygen in the system DO at these levels are unlikely to affect food safety, however DO levels in outlets that fall lower than 5mg/l may have an impact on the environment, and plants and animals in the surrounding aquatic

ecosystem Under normal stream conditions 3.0mg/l or less, of DO is regarded as hazardous for a significant variety of fish fauna (Ellis 1937)

Hue - DO

2.5 3.5 4.5 5.5 6.5 7.5

Outlet Ponds

Figure 5: Dissolved oxygen levels in inlets, outlets and ponds

3.5 Water temperature

There was little difference in the water temperature between water sources in any of the provinces (Figure 6) For shrimp production, it is recommended that the temperature remains between 25 and 33oC for maximum production Temperature remained within this range in all provinces Temperature increased over the season

in all provinces, and experienced significant increases mid-season in TT-Hue and Nghe An corresponding to the drop in salinity and pH of the water

As temperature levels both in the inlet and outlet channels effectively mirriored the temperature in the ponds, and were similar to baseline readings (Ha and Suc 2007),

it is highly unlikely that there would be an impact on the surrounding environment Water temperature would only affect food safety if the product was harvested and not put on ice immediately and handled properly throughout the packaging and transporting process The temperature of the ponds alone would have no effect

Environmental and Economic Evaluation of Shrimp Culture Practices in Vietnam

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Hue - Temperature

24 26 28 30 32 34

Inlet Outlet Ponds

Figure 6: Water temperature levels in inlets, outlets and ponds

3.6 Ammonia (NH3)

Ammonia levels were consistently low in all water sources and provinces throughout the season (Figure 7) Levels were below 0.1mg/l in all sources, which is the maximum recommended level for Vietnam (internationally, Chin & Chen (1987) consider 0.13mg/l of ammonia to be a safe level for shrimp pond conditions) Generally, ammonia levels were found to be higher in the outlets than in the ponds and inlets Levels of ammonia in the outlet channels were not significantly high and would be unlikely to impact the environment or food safety standards Ammonia is more toxic when dissolved oxygen concentration is low, however with increasing carbon dioxide (which occurs when DO is low) the toxicity of ammonia decreases (Boyd 1990)

Hue - NH3

0 0.02 0.04 0.06 0.08

Outlet Ponds

Figure 7: Ammonia levels in inlets, outlets and ponds

3.7 Alkalinity

Alkalinity averaged approximately 85mg/l in all water sources, although it increased significantly to approximately 100mg/l in Ha Tinh during the end of the data collection period (Figure 8) This increase corresponds to a drop in temperature, salinity and pH Alkalinity in all water sources generally remained within the safe range of 80-120 mg/l Alkalinity is defined as the sum of exchangeable bases reacting to neutralise acid when an acid is added to water Alkalinity plays two important roles in water Bicarbonates, and carbonates to a lesser degree, are a storehouse of carbon needed in photosynthesis for phytoplankton growth They also constitute the major buffering system to reduce fluctuations in pH Alkalinity levels

in outlets and inlets at all times during the trial was unlikely to have any impact at all

on the environment or affect food safety

Hue - Alkalinity

60 80 100 120

Outlet Ponds

Figure 8: Alkalinity levels in inlets, outlets and ponds

3.8 Nitrite

There are significant differences in nitrite levels across provinces and water sources (Figure 9) It is recommended that nitrite levels remain below 0.30mg/l to maximise shrimp production Whilst sub-lethal concentrations of nitrite increases the susceptibility of fish to bacterial diseases (Hanson & Grizzle, 1985), nitrite levels were significantly lower than this level for all water sources in TT-Hue, and generally for inlets and ponds in Ha Tinh and Nghe An As there are many factors which affect the nitrite toxicity in fish and shrimp ponds (eg chloride concentration, pH, animal size, previous exposure, nutritional status, infection and dissolved oxygen concentration

(Schwedler et al 1985)), it is difficult to pinpoint one variable However, attention to

dissolved oxygen is again highlighted as important

Environmental and Economic Evaluation of Shrimp Culture Practices in Vietnam

Research Institute for Aquaculture No 1 & The University of West Australia 16

Hue - Nitrite

0 0.05 0.1 0.15 0.2 0.25 0.3

Outlet Ponds

Figure 9: Nitrite levels in inlets, outlets and ponds

3.9 Sulphides

It is recommended that sulphides remain below 0.2mg/l for maximum production Sulphide levels in TT-Hue were consistently and significantly below this level for all water sources in TT-Hue, and for inlets and ponds in Ha Tinh and Nghe An (Figure 10) Sulphide levels were higher than recommended in the outlets in Nghe An, and in

Ha Tinh at the beginning of the season Toxic amounts of hydrogen sulphide block the electron transport system and stops oxidative respiration Blood lactate concentrations also increase and anaerobic glycolysis is favoured over aerobic respiration, suggesting that the toxic effect is hypoxia Therefore, increased levels of dissolved oxygen are desirable (Boyd, 1990) Hydrogen sulphide toxicity is also more common in acidic environments as pH decreases As hydrogen sulphide is toxic at low concentrations and egg survival and fry development of fish can be limited by 0.006mg/l H2S, impact on the environment should be monitored If the pond water can be aerated prior to discharge this would minimise the environmental impact of

H2S At the levels reflected in these data food safety is not a concern

Hue - Sulphide

0 0.01 0.02 0.03 0.04

Outlet Ponds

Figure 10: Sulphide levels in inlets, outlets and ponds

2 Dissolved oxygen was lower than recommended in Nghe An,

3 Salinity was lower than recommended in TT-Hue, and higher than recommended in Ha Tinh,

4 Sulphides were within the recommended range for all ponds, although higher than recommended for outlets in Ha Tinh and Nghe An,

5 Transparency was high at the beginning of the cultivation period in all provinces, but fell to within the recommended range in Ha Tinh and Nghe An towards the end of the period,

6 An increase in alkalinity in Ha Tinh corresponded to drop in temperature, pH and salinity, and

7 Environmental quality data analysis shows that it is unlikely that the shrimp aquaculture systems tested will have an adverse effect on the environment or food safety One exception to this is dissolved oxygen levels, which were low

in the output channels and my be hazardous for fish fauna Low dissolved oxygen also increases the toxicity of nitrites and sulphides in outlet channels Pond water aeration prior to discharge is likely to negate these impacts

Environmental and Economic Evaluation of Shrimp Culture Practices in Vietnam

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4 Household Shrimp Production

Data and analysis on household shrimp production is presented in the following six sub-sections:

1 General information on household operations,

2 Environmental and water quality data,

3 Chemical and microbial analysis,

4 Costs of production,

5 Production volume and value, and

6 Profit and Benefit Cost Ratio

4.1 General information on household operations

Nine households participated in the BMP trials, three from Thua Thien-Hue (TT-Hue) (households 1 to 3 in Table 1), three from Nghe An (households 4 to 6 in Table 1) and three from Ha Tinh (households 7 to 9 in Table 1) The average size of the shrimp culture ponds was 0.44ha, ranging from 0.25ha to 0.68ha This average pond size is smaller than the average of non-BMP shrimp farmers in the same provinces

(0.69ha) (Thanh et al 2007)

Table 1: Household name, location, pond area and culture type

Location of household Area of culture

pond (ha)

Stocking density (shrimp/m 2 )

Culture type

1 Phongchanh, Vinhhung, TT-Hue 0.68 7.9 Improved-extensive

2 Phongchanh, Vinhhung, TT-Hue 0.36 13.9 Improved-extensive

3 Phongchanh, Vinhhung, TT-Hue 0.50 10.0 Improved-extensive

4 Hunghoa, Hunghoa, Nghe An 0.25 24.0 Semi-intensive

5 Hunghoa, Vinh, Nghe An 0.45 22.2 Semi-intensive

6 Hunghoa, Vinh, Nghe An 0.50 10.0 Improved-extensive

7 Hongha, Thachha, Ha Tinh 0.50 18.0 Semi-intensive

8 Lienha, Thachha, Ha Tinh 0.50 20.0 Semi-intensive

9 Lienha, Thachha, Ha Tinh 0.25 24.0 Semi-intensive

Four of the nine shrimp farmers who participated in the trials also have ‘containing ponds’ which are used for water conditioning and processing These ponds average 0.19ha (ranging from 0.10 to 0.25ha)

The average stocking density was 16.7 shrimp/m2, which is almost double that of non-BMP households where the stocking density is 8.4 shrimp/m2 (Thanh et al

2007)

Culture type is defined by stocking rate according to the following guide:

• < 8 shrimp/m2 – Extensive

• 8 – 15 shrimp/m2 – Improved extensive

• 15 – 25 shrimp/m2– Semi-intensive

• > 25 shrimp/m2– Intensive

The households who participated in the farm trials are either improve-extensive or semi-intensive farmers All farmers in TT-Hue are improved-extensive farmers All other farmers are semi-intensive except for one farmer in Nghe An

4.2 Environmental water quality data

This section presents data on environmental water quality parameters collected by household members They are the same nine parameters as measured by Extension Officers for the shrimp systems as presented in Section 3, and are located in the same three provinces Table 2 presents average, minimum and maximum water quality readings from a 10-17 week culture period from March/April to June/July

2007 (the exact timing of the readings depends on the farm)

4.2.1 Transparency

Although the average transparency reading for all households was approximately

37cm, within the recommended range of 25 – 40cm for maximum production, almost all ponds had higher than recommended maximum levels, and one pond also fell below the recommended minimum of 25cm

Data was missing from ponds 6, 7 & 8, and patchy data for 4, 5 & 9, however farms from the other ponds noted in detail water colour and corrective measures taken if the colour changed from ideal green to strong green Pond 3 in TT-Hue seemed to have the most consistent colour from green to strong green and to yellow These transparency levels are unlikely to have an impact on the environment, or affect food safety, as it is purely an optimal range for the best growth of the shrimp

4.2.2 Salinity

The average salinity reading for all households was approximately 19%o, which is within the recommended range of 15-25%o for maximum production Salinity was low in TT-Hue, with two farmers having lower than recommended salinity levels (even though it may be expected that warmer ambient air temperatures in this region would encourage evaporation and therefore increase salinity levels) Overall, salinity was higher in Ha Tinh and Nghe An, with higher than recommended readings

on some of the ponds in those areas These salinity levels are unlikely to have an impact on the environment or food safety Ha and Suc (2007) indicate a range of 13-24%o for the three areas prior to stocking

4.2.3 pH

pH in the mornings (average 7.93) and evenings (average 8.10) did not venture greatly outside the optimum range of 7.50 – 8.50 for maximum production Generally, pH was found to be slightly higher in the evenings than in the mornings

pH levels are unlikely to have an impact on the environment or food safety Ha and

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4.2.4 Dissolved oxygen levels seemed to be a widespread problem with a number

of minimum and maximum readings falling below the acceptable 5.00mg/l, especially

in the mornings, and will thus not enhance maximum growth of this species DO at these levels are unlikely to affect food safety, however DO levels in outlets that fall lower than 5mg/l may have an impact on the environment, and plants and animals in the surrounding aquatic ecosystem Under normal stream conditions 3.0mg/l or less,

of DO is regarded as hazardous for a signicant variety of fish fauna (Ellis 1937)

4.2.5 Temperature readings were consistently between the optimum of 25–33oC for maximum production Ponds in Ha Tinh and Nghe An had maximum temperatures higher than the recommended temperatures As the temperatures did not deviate greatly from the ambient, it is highly unlikely that there would be an impact on the surrounding environment Water temperature would only affect food safety if the product was harvested and not put on ice immediately and handled properly throughout the packaging and transporting process The temperature of the ponds alone would have no effect

4.2.6 Ammonia (NH 3 ), almost all readings fell within the safe range for production

and environment of 0.00–0.10 mg/l Levels of ammonia were not significantly high and would be unlikely to impact the environment or food safety standards Ammonia

is more toxic when dissolved oxygen concentration is low, however with increasing carbon dioxide (which occurs when DO is low) the toxicity of ammonia decreases (Boyd 1990)

4.2.7 Alkalinity readings were consistently between the optimal range of 80–

120mg/l Two farms each in TT-Hue and Nghe An dropped below the optimal range, but it is not expected that this would impact shrimp production, and was unlikely to have any impact at all on the environment or affect food safety

4.2.8 Nitrogen Dioxide (NO 2 ) and Hydrogen Sulphide (H2S) levels were all

within the safe range throughout the season and in all ponds, and are unlikely to have any impact on the environment or food safety

Table 2: Environmental water quality parameter of households

Transparency (cm) Salinity (%o) (AM) pH (PM) pH DO mg/l (AM) DO mg/l (PM) Temp (AM) oC Temp (PM) oC NH3

(mg/l) Alkalinity (mg/l) (mg/l) NO2 (mg/l) H2S

Optimal

range for

Note: Bold figures indicate that the value falls outside the optimal range for Vietnam

n.a = not available