Manu Potaros, Department of Fisheries, Bangkok.
Thailand is currently the world's leading producer of shrimp. Intensive shrimp aquaculture is well developed along the Thai coastline.
This country report from Thailand concentrates on shrimp farming as it is in this aquaculture sector that interactions between aquaculture and the environment are most pronounced. Until about 10 years ago, Thailand was mainly involved in extensive shrimp culture of Penaeus merguiensis. When the commercial production of P. monodon commenced, shrimp farm area expanded from 4 to 23 provinces and production increased dramatically. The rapid development of the shrimp culture industry has caused serious environmental impacts including: (i) the destruction of coastal mangroves; (ii) shrimp pond effluents have caused pollution of natural waters, including seawaters; and (iii) serious shrimp disease outbreaks, due mainly to self-pollution and a deteriorating pond environment. Methods to reduce the negative impacts of shrimp farming in Thailand, to ensure that it has an environmentally sustainable future, are described in this report.
Shrimp farms have operated along the coast of the Gulf of Thailand for more than 50 years, originating in the Inner Gulf at Samut Prakarn Province. Originally, paddy fields were converted to shrimp ponds by flooding them with seawater during the monsoon season. The incoming sea water, laden with shrimp seed, was confined in the field for 3–4 months (until the shrimp reached market size), after which the water was drained out through sluice gates and the shrimp collected with a bag net. The main species produced were Penaeus merguensis (banana or white shrimp). About 10 years ago, Thailand succeeded in culturing hatchery seed on a commercial scale and many hundreds of millions of shrimp seeds were produced. This accelerated the development of shrimp farming into semi-intensive culture and finally, intensive culture systems. The coastal area devoted to shrimp farming expanded from 4 provinces in the Inner Gulf (Bangkok, Samut Prakarn, Samut Sakorn and Samut Songkran) to the whole coastal area of 23 provinces. As the seed which is mass produced is Penaeus monodon (black tiger shrimp), this subsequently became the main cultured species.
Map of Thailand.
Due to the rapid expansion of shrimp farming, the production of cultured shrimp increased from 1,590 tonnes in 1977, to 10,091 tonnes in 1982 and 23,566 tonnes in 1987. After 1987, shrimp farms along the Inner Gulf (Bangkok, Samut Prakarn, Samut Sakorn and Samut Songkram) began to face water quality problems, so shrimp farmers moved down to the east and south coasts of Thailand, and finally across to the coast of Andaman Sea. Highly intensive farming methods were used and the production of cultured shrimp increased each year, standing at 162,070 tonnes in 1991 and 162,692 in 1992. It is likely that the production of cultured shrimp in Thailand is now at its maximum level and will not exceed 200,000 tonnes annually (see Tables 1 and 2).
In Thailand most shrimp farm products are for export. In 1992, Thailand exported 124,399 tonnes of shrimp product with an estimated value of 31,113 million Bahts. This is around half of the total value for the export of aquatic products. The role of cultured shrimp production in the economy of Thailand is shown in Table 3.
Table 1. Shrimp farm area (rai) along the coast of Thailand, 1987–1991.
|Nakorn Si Thammarat||46,735||37,748||47,754||62,500||69,841|
Note: 6.25 rai = 1 ha.
The total pond area of shrimp farms in Thailand was 470,826 rai in 1991 with 18,998 farms, which provide work for approximately 114,000 people. There are more than 2,000 private hatcheries which employ around 20,000 people. In addition, there are cold storage and processing plants for shrimp products plus feed mills, about 250 plants in total, with more than 200,000 men. Apart from this, investors and banks gain benefit by providing credit with greater than 1,000 million Bahts in circulation at interest rates of 15–17%.
A case study of intensive farming of black tiger shrimp which included 20 farms, was conducted by the Department of Fisheries (DOF, 1992) and analysis of the results (Table 4) revealed that the total cost of shrimp production was 82,730 Bahts/rai, which comprised 55,627 Bahts of cash costs and 27,103 Bahts non-cash costs. The variable cost was 53,697 Bahts/rai which was 64.9 % of the total cost. The study showed that feed costs were the highest variable cost, representing 33.7 % of total costs. The second highest variable costs were seed costs, representing 11.4 % of the total cost. Fixed costs were 29,033 Bahts/rai representing 35.1 % of total cost. Fixed costs were comprised of cash costs of only 4,381 Bahts and non-cash costs of 24,652 Bahts. The net operating profit was 11,101.5 Bahts/rai (Table 5).
Table 2. Shrimp production in Thailand (tonnes).
|Year||Cultured Shrimp Production||Wild Shrimp Production|
Table 3. Value (millions of Bahts) of shrimp product to the GDP of Thailand.
|Year||Value of shrimp product||% of GDP|
Table 4. Cost of shrimp production from intensive pond culture (1 rai/pond).
|Cost Item||Cash Costs||Non-cash Costs||Total||% of total|
|Depreciation of pond and sluice gate||-||5,993||5,993||7.2|
|Depreciation of equipment||-||8,915||8,915||10.8|
|Depreciation of housing||-||561||561||0.7|
|Teaseed cake and lime||1,170||-||1,170||1.4|
|Drugs and other chemicals||2,147||-||2,147||2.6|
|Gasoline and lubrication||4,684||-||4,684||5.7|
|Pond bottom clearing||3,220||-||3,220||3.9|
|Pond and sluice gate repair||1,160||-||1,160||1.4|
25.5 Bahts = 1 US $; 1 rai = 1,600m2; 1 ha= 6.25 rai.
Table 5. Production cost and income from intensive pond culture of black tiger shrimp.
|ITEM||per rai||per kg|
|Production of black tiger shrimp (kg)||659||-|
|Net profit over variable cost||40,234||60.9|
|Net profit over cash cost||38,304||58.0|
A comparison of the income and benefit of shrimp farming compared with that of rice farming may be made using data from poor-grade paddy production costs in 1992 (Table 6). The country average for poor grade paddy production costs in 1992 was 2,573.5 Bahts/tonne. One rai of paddy field yielded 641 kg/crop and the farm price of poor grade paddy was 3,060 Bahts/tonne. The income from one crop of poor grade paddy plantation from one rai area of land was 1,961.5 Bahts, with a net profit of 314 Bahts/rai.
In the case of producing good grade paddy, the net benefit from one rai land was 331.7 Bahts (production 307 kg/rai, cost of production was 3.12 Bahts/kg and farm price 4.20 Bahts/kg). In one rai of land, a net benefit of 11,101.5 Bahts can be made by culturing shrimp, but capital investment is up to fifty times greater and more experience in farm management is needed compared with rice cultivation.
As mentioned earlier, shrimp farming practices in Thailand have developed gradually. The pattern of practice and management can be identified as follows:
This is the original shrimp culture system used at the start of shrimp farming in the Inner Gulf area of Thailand. Farm practices were based on natural seed supply, the conversion of rice fields with the construction of high dikes around it and the installation of a sluice gate, which allowed seawater to pass through during high tide. Shrimp farmers opened the sluice gate to receive seawater containing shrimp seed and nutrients and retain them in the field. Most of the incoming shrimp seed were banana shrimp (Penaeus merguiensis).
Water levels in the field were maintained at depths of 50–60 cm, so the shrimp farms had to be close to the sea, which is also mangrove area. During high tides, sea water would be drained into the field every day to maintain water levels in the ponds. After 3–4 months, when the shrimp had grown to market size (40–50 shrimps/kg), the water was drained out through the sluice gate during low tide and the shrimp were trapped using a bag net set at the sluice gate. Before a new crop of shrimp was started, the dike was repaired and the ditch scoured. These systems produced two crops of shrimp per year: the first during the north-east monsoon season (November-February) as this is a period of high salinity sea water. The main product at this time is banana shrimp, which can live and grow well in high salinities and high yields of 25–30 kg/rai can be attained. The second crop of shrimp is during the rainy season (during the south-west monsoon) with low salinity sea water. The main product will be Metapeneaus sp. shrimp which grow well in low salinities. Yields of this crop will be less than the first crop. Extensive shrimp farmers usually have large farms (50–300 rais) in order to get enough economic return to keep a family. Farmers try to increase shrimp production by draining more seawater into the field with the aim of increasing shrimp seed and nutrient intake. The pumping of sea water is by water wheel run by windmill or diesel engine.
Table 6. Cost of poor grade rice production from a one rai rice field in 1992 (Bahts).
|Item||Cash Costs||Non-Cash Costs||Total|
|Seed preparation and seedlings||30.0||56.5||86.5|
|Weeding and other care||17.6||190.1||207.7|
|Expense after harvesting||125.8||99.7||225.5|
|Insecticide and herbicide||70.0||-||70.0|
|Gasoline and lubricant||30.7||-||30.7|
|Equipment and other supplies||7.2||-||7.2|
|Repair of tools||2.7||-||2.7|
|Interest and opportunity costs||31.8||20.0||51.8|
|Tax and land-use||20.2||133.5||153.7|
|Depreciation of tools||-||12.2||12.2|
Cost per rai
|Variable costs per kg paddy||2.3|
|Total cost per kg paddy||2.6|
|Total cost per tonne of paddy||2,573.5|
|Paddy construction per rai (kg)||641|
In this system, farm management is improved and hatchery seed are used. The Department of Fisheries (DOF) successfully produced shrimp seed of both banana shrimp and black tiger shrimp in 1983. This was necessary as the natural supply of shrimp seed were becoming depleted. The stocking of hatchery seed allows natural populations to recover. The eradication of wild fish is achieved using teaseed cake, which maintains a high survival rate of the shrimp. The dimensions of shrimp farms change with semi-intensive systems, the area is reduced to 20–30 rais, often equipped with water storage. The stocked species are banana shrimp and black tiger shrimp with stocking densities of 5–10 pieces/m2. The seawater is drained into the ponds by a pushing pump, which handles the higher quantity of sea water more easily. Additional feed is applied so that the yield of shrimp increases to 60–100 kg/rai in a 4 month period.
The development of intensive culture was made possible by the large scale production of seed by the Department of Fisheries and the private sector, with 3–4,000 million produced annually. The large, shallow semi-intensive ponds were converted to 1–5 rais in area and water depths increased to 2–2.5 m. Stocking rates were up to 50–100 pieces/m2. Due to the poor tolerance of banana shrimp in poor water quality, the more tolerant black tiger shrimp is stocked. Also tiger shrimp can grow up to a size of 30–40 pieces/kg in a 4 month culture period, which is better economically as large shrimp fetch a higher price than small shrimp. In intensive farms, heavy feeding rates are applied and after 100 days of culture the pond bottom will form anaerobic conditions, with low dissolved oxygen levels and high concentrations of toxic gases, such as hydrogen sulphide, ammonia, nitrite and carbon dioxide. These conditions will kill banana shrimp but are not as harmful to the black tiger shrimp. In intensive systems, the chemical condition of the water and dissolved gases may be a serious threat to shrimp health. Dissolved oxygen levels in the water column have to be kept at over 5 ppm and additional dissolved oxygen is supplied by paddle wheel or air jet machine. Water is also exchanged at a rate of 10% fresh seawater per day. In intensive systems, a pipe-pumping engine is used instead of a pushing pump because of the distance of the high dike from the sea, the smaller volumes of sea water, smaller size of pond and shorter pumping times during high tide.
The stocked shrimp are fed with high quality complete feeds, with a protein content of over 45%, supplemented with vitamins and minerals. The feeding schedule must be at least 4–5 times/day and the quantity of feed fed should be adjusted every 15 days. In converting extensive or semi-intensive ponds to intensive ponds, the farmers need to remove top soil of the shrimp pond. In general, the sub-soil in mangrove areas has a very high acidity (with pH of around 3–4) caused by the pyrite soils and sub soils. The soil acidity problem can only be solved through time, entails high costs and will be very difficult to manage. Intensive culture requires a 4–5 month culture period with the yields of 0.8–0.9 tonnes/rai to 2 tonnes/rai, depending on the farm environment, experience of the management and capital support. On average over the country, yields are 0.6–0.7 tonnes/rai and 2–2.5 crops can be produced annually.
Most suitable lands can be utilised for shrimp farming. The use of mangrove for shrimp farms is, however, regulated and shrimp farms can only be developed in designated areas and with the permission of the Department of Forestry. The returns from shrimp farming are very high, which has attracted people from various professions to invest in the business. The development of shrimp farming was not pre-planned, so shrimp farms are scattered randomly throughout the coastal area which causes impacts to nearby plantations and water sources used by animals. Despite this, the shrimp farming business is still in operation because shrimp farmers have enough money to pay for conflict or damage.
3. IMPACT OF THE RAPID DEVELOPMENT OF THE SHRIMP CULTURE INDUSTRY ON THE ENVIRONMENT
The growth of cultured shrimp production brings in foreign exchange, but at the same time results in negative impacts on the environment. These are:
3.1 Exploitation of mangrove
The utilisation of mangrove for shrimp culture has an effect on the ecological balance of coastal areas. The DOF has never recommended that shrimp farmers use mangrove land for culture for various reasons, including:
Although coastal mangrove land is close to the sea and seawater can be easily drained into the shrimp ponds (which is why extensive farming was initiated in these areas), in reality, land in mangrove areas is not suitable for shrimp farm construction, because:
There are many plant roots and stumps which are difficult and costly to remove.
Mangrove areas belong to the public and are directly under the control of the Department of Forestry. The Department of Forestry cannot efficiently protect the mangrove due to manpower and budget limitations. The cutting down of mangrove trees for charcoal production was permitted but no attention was paid to reforestation, so mangrove deterioration existed prior to the development of shrimp farming, which gave invaders the opportunity to mis-use the mangrove area.
Expansion of shrimp culture in Thailand was very rapid and there were no plans in place to cope with the rapid growth. There was a lack of infrastructure such as land-use planning, seawater supply canals and waste water drainage canals, road systems, electricity facilities and other services for the shrimp farming industry.
However, the shrimp culture industry is not the only source of damage to the mangrove. Shrimp farms account for only 38% of the total destroyed mangrove land (Table 7). Suitable land for shrimp farming are in areas beyond the mangrove. This was observed after the failure of shrimp farming in the Inner Gulf of Thailand when many shrimp farmers moved to the Andaman coast and constructed shrimp ponds in the rice fields beyond the mangrove. These lands tend to be privately owned.
Table 7. Reduction of mangrove land compared to area converted to shrimp farms.
|Year||Mangrove area (rai)||Reduction in mangrove (rai)||Percentage reduction in mangrove||Shrimp Farm (rai)|
2.2 Shrimp farm effluents pollute coastal seawater
Discharge waters from shrimp ponds contain silt and organic substances (waste feed and excretory products of shrimp) as well as some toxic chemicals (used for killing shrimp predators), fertilisers, lime and other minerals. As a result of the process of organic digestion, a layer of anaerobic sediment may form in the ponds, micro-organisms will consume more oxygen and high quantities of carbon dioxide, hydrogen sulphide, ammoniacal nitrogen and nitrite will be produced. High concentrations of these chemicals and the anaerobic conditions in the ponds may be harmful to, or kill, the shrimp. The final product from the digestion of organic material is nutrients for micro-organisms which are in turn food for shrimp, bivalves and fish. At Tha Tong Bay in Surat Thani Province, there are shrimp farms along the coastal area and oyster and bloody cockle beds in the coastal seawaters which receive the wastewaters from shrimp farms. Many thousands of tonnes of oysters and bloody cockle are produced annually. At Ranod and Sating Pra District in Songkhla Province, there are 15,000 rais of shrimp farms in the coastal area and beyond the shrimp farms is sandy beach that was always a poor area for swimming crab. After the shrimp farms were developed and discharged wastewater to the sea, the number of swimming crabs were found to increase and there are now plenty, although no statistical study has been carried out.
There is a consensus of opinion that waste water and silt from shrimp ponds is a cause of water pollution in the coastal environment, however, it is only one of many sources of pollution. This can be clearly seen at the mouth of main rivers on which crowed cities and large numbers of factories are sited. In the case of the Inner Gulf of Thailand, which receives the flow of the rivers: Chao Phrya, Tha Chin, Mae Klong and Petchaburi, in whose basins there are crowded residential areas (with ⅓ of the country's population) and tens of thousands of industrial plants. Effluent from cities contains domestic and industrial pollutants and is composed of organic and inorganic substances and heavy metals residues. In 1990, a study was conducted by the Coastal Aquaculture Division of the Department of Fisheries on water quality and heavy metal residues in the Tha Chin River, one of the main rivers flowing from the central plain of Thailand into the Inner Gulf (Table 8). This river is the situated in Samut Sakorn Province, in the centre of the shrimp culture area. The results revealed that the river is 325 km in length, flows through 4 provinces including 20 large, crowded cities with a population of approximately six million (DOF, 1990). There were 52 plants or factories including, 33 cloth dying factories, 4 fish sauce factories and 1 alcohol distillery. There are rice and fruit tree plantations and pig farming. Quantities of heavy metal residues in the river have increased ten fold over the last six years.
Table 8. Heavy metal residues in the Tha Chin River in January, 1990.
|Mouth of River||0.12||0.05||0.10||0.33|
Source: Coastal Aquaculture Division, Department of Fisheries.
When effluents from cities combine with wastewater from shrimp farms a severely toxic mixture results, especially for shrimp culture. Since 1987, shrimp farms in the Inner Gulf of Thailand area (Bangkok, Samut Sakorn, Samut Prakarn, Sumut Songkran and Petchaburi) an area about 148,765 rai had to be closed down, as the seawater sources used by the shrimp farmers were polluted. At first it was believed that such poor water quality was the result of waste effluents from shrimp culture, but two years after the shrimp farms ceased operating the polluted condition of the water had not reduced. It can thus be concluded that pollution from cities is the main agent causing damage to the environment. The main causes of water pollution in Inner Gulf may be summarised as follows:
There are many crowded cities and industrial plants depositing waste into the water resources.
The Inner Gulf has a closed shape and is shallow. Waters discharged from rivers and canals cannot travel a long distance from the coast, so it flows circularly within the gulf.
Greater volumes of freshwater from the main rivers are being used for irrigation. The amount of freshwater to dilute the wastes is therefore less, so the wastes accumulate.
The enforcement of pollution control legislation is rather weak.
Drainage canals are shallow and the mouths of rivers and canals are closed with sand or sediments. The effluent from shrimp farms cannot flow out to the deep sea and flows back to the shrimp farms at the high tide.
Only intensive shrimp culture causes water pollution, due to the heavy application of feed and chemicals, but intensive farms comprise only 46% of the total farm area.
Chemical analysis of sea water shows that water quality along the coasts which have no densely populated cities or industrial plants is better than water quality along parts of the coast which have cities with dense populations and industrial plants (Table 9). It can be concluded that the deposit of shrimp farm effluents into coastal waters will not permanently pollute the environment.
Table 9. Water quality in coastal areas in 1992.
|Province||Surat Thani||Prachuab Kiri Khan||Chasearng Sao||Samut Sakorn|
|Location||Mouth of Klong Tha Thong||Klong Bang Nang Rom||Klong Wan||Mouth of Bang Pakong||Coastal Area||Mouth of Subpa Samit||In Subpa Samit Canal|
|pH||5.1 – 8.2||7.4 – 8.4||7.4 – 8.2||6.7 – 8.0||7.6 – 8.5||6.4 – 9.0||7.4 – 8.4|
|Dissolved oxygen (mg/l)||2.8 – 11.2||3.3 – 11.7||4.3 – 9.2||4.1 – 8.8||1.1 – 11.8||1.1 – 7.5||0.3 – 7.5|
|BOD (mg/l)||0.8 – 7.7||nd||nd||nd||nd||nd||nd|
|Nitrite (mg/l)||0.002 – 0.022||0.007 – 0.48||0.002 – 0.07||0.005 – 0.122||0.1||0 – 0.05||0.1 – 0.18|
|Ammonia (mg/l)||0.001 – 0.95||0.0 – 0.475||0.0 – 0.30||0.07 – 0.70||0.2||0.007 – 0.3||0.044 – 0.46|
|Phosphate (mg/l)||0.00 – 0.59||0.008 – 0.48||0.05 – 0.42||0.00 – 0.05||0.25 – 3.0||0.01 – 0.48||0.02 – 0.13|
|Description||No sewage or industrial waste. Suitable for shrimp culture.||As before and have oyster farm.||No sewage. Water source of shrimp and fish hatchery.||Sewage from small town. No industrial plants. To be used for shrimp culture.||Coastal Area: Sewage from big town with many industrial plants. Also shrimp effluents. Not suitable for shrimp farming.|
3.3 Source of diseases in shrimp culture
In intensive shrimp culture, ponds are stocked at high densities (50–100 post-larvae/m2 or higher), which results in the application of high quantities of feed. Uneaten feed and shrimp faeces will accumulate at the bottom of the pond and will be decomposed, which may cause low dissolved oxygen levels and unfavourable water quality conditions in the pond. In addition, nitrogen and phosphorus produced from the decomposition of organic material will promote the growth of phytoplankton. When phytoplankton blooms die, the plankton will also be broken down which further reduces oxygen levels and stimulates decomposition in the pond. These activities encourage the growth of micro-organisms such as protozoa, bacteria, fungus and virus which are parasites and disease vectors of shrimp.
Outbreaks of shrimp disease often occur when the shrimp have been stocked for one month in an old pond. The disease is caused by the bacteria group Vibrio which grow well in shrimp faeces. If water and feed management practices at the farm are not good other diseases will infest the farm over the months prior to harvesting. The most common diseases are:
Ectocommensal fouling disease. This is the result of an attachment of the protozoan groups Zoothannium, Acinecta, Uphelota, Tokophrys and other algae on the gill, appendages and shell of the shrimp.
Swollen tail disease and tail rot disease. This is a bacterial infection on the tails of shrimp.
Black gill disease. This is where the gills are covered with a Fusarium fungus, bacterial infections and an accumulation of dead phytoplankton. Gill colours such as brown, tan and yellow are caused by dying phytoplankton and red coloured gills are usually observed at night when dissolved oxygen is low.
Monodon baculovirus (MBV) disease. This is the result of the MBV (Monodon baculovirus) infection in the hepatopancreas.
Black splinter disease. This is formed by changes in the connective tissue when shrimp haemocytes surround the bacteria.
Cotton disease (milky disease). The entire dorsal side of the shrimp, or a section of the body, will have groups of spores under the shell which have a milky white appearance.
Crooked leg disease. This is caused by calcium deficiency in the water (low alkalinity).
All of these diseases occur as a result of high stocking densities of shrimp seed and improper management of the pond environment.
4. AN ECONOMIC ASSESSMENT OF THE MAGNITUDE OF THE DAMAGE
Shrimp culture in Thailand expanded all over the coastal area until it impacted on the environment, particularly with the destruction of mangrove and water pollution. A study of the economic damage caused by those impacts was not carried out, but some estimations can be made.
4.1 Destruction of mangrove
At present, there are approximately 4–5 hundred thousand rai of shrimp farms but the destroyed area of mangrove is 1.2 million rai. It has been estimated that shrimp farms occupy an area equivalent to 38% of the total destroyed area of mangrove. If an effective survey was made, it would show that the area of shrimp farms which occupy the mangrove must be less than present area of shrimp farms as, especially on the Andaman Sea coast, most shrimp farms (18,441 rai) are out of mangrove areas. In addition, the mangrove area that has been used for shrimp farms is often previously degraded forest so it is very difficult to assess the economic damage related directly to shrimp farming.
Sources of water pollution in coastal areas are derived from cities and shrimp farm wastes. These wastes will pollute both the natural environment and water supplies for shrimp farms. Shrimp farm wastes are made up of organic substances and when it is broken down, the final products will be nutrients which can sustain plant life. If it is properly managed, the coastal environment adjacent to shrimp farming areas could have sustainable fertility. However, the effect of closing shrimp farms in the 5 provinces of the Inner Gulf of Thailand may be estimated from the statistical data. It has been shown that the area of shrimp farms closed in 1990 and 1991 was 124,374 rai in total, which was comprised of 9,085 rai of extensive farms, 39,885 rai of semi-intensive farms and 75,404 rai of intensive farms. The cost of the damage has been calculated from the value of expected shrimp production and the value (or depreciation cost) of ponds and equipment. The cost of the damage was 4,135.6 million Bahts or approximately US $ 162.2 million.
5. AN ANALYSIS OF WHAT COULD HAVE BEEN AND IS BEING DONE TO MITIGATE OR AVOID THE DAMAGE
After concerned people were made aware of the problems of industrial shrimp farming, both the Government and the private sector have tried to protect the environment and solve the problems.
5.1 Government activities:
5.1.1 Maintenance of coastal environment
The Department of Fisheries has limited the area of farms and production of shrimp to not over 5 hundred thousand rai (80,000 hectares) and 200,000 tonnes per year, respectively, in order to protect the coastal environment.
To promote recovery of the environment where a deterioration has occurred, through controlling farm management practices and the discharge of effluent into receiving canals. The Ministerial directive dated 18 November 1991 (BE 2534) was declared and the shrimp farm operators needed to be registered with the District Fisheries Office. Shrimp farms with water areas above 50 rai (8 hectares) have to construct a waste storage pond of 10% of the size of the whole water area of the farm. The BOD value of discharged wastewater from the farm will not exceed 10 ppm. In addition, shrimp farm operators who discharge the bottom residues from ponds will be fined or jailed.
A monitoring program for analysing the chemical properties of coastal waters will be made by the Coastal Aquaculture Development Centres and Stations. The data generated will be distributed to nearby farmers to advise them of coastal water quality and to remind them not to drain poor water from their shrimp ponds.
The Department of Fisheries has implemented a project of improving drainage canals and tributaries. In this project, 147 natural canals and tributaries with a total length of 670 km have been excavated and scoured. In addition, water ways with a length of 816 km in shrimp farming areas have been deepened. This programme will take 5 years to implement (1990–1994) and the budget is 460 million Bahts (US $ 18.07 million). The programme is being implemented in a potential area of 24 coastal provinces. After 1994, the project will be turned into the routine work of the provincial authorities. The aim of the project is to maintain and sustain the existing shrimp farming industry.
4.1.2 Maintenance of the mangrove
The people will be made aware, by various educational means, of the importance of preserving the mangrove. At the same time there will be a strengthening of the protection afforded under mangrove law and enforcement will be applied. Nine Cabinet resolutions have been made, but only the essential ones will be mentioned in this paper.
1. Cabinet resolution on 15 December 1987, it was mentioned that the zonation of mangrove will be separated into 2 areas: a conservation zone and an economic zone.
Conservation zones cover 426.78 km2 of mangrove and will be reserved in their natural state for environmental and ecological purposes, such as:
sanctuary of plants and animals;
propagation and breeding of plants and animals;
areas that are easy to destroy through erosion;
areas of local principle symbol;
wind break and break water areas;
areas for scientific study;
areas for ecological and environmental reserve;
areas not beyond 20 m distance from river and canals and 75 m distance from the coast.
Economic zones cover an area of 3,297.7 km2 of mangrove and are divided into:
Economic Zone A: This area will be reserved for forestry activities and covers 1,996.89 km2 of mangrove.
Economic Zone B: This is the area not included in Economic Zone A and will be reserved for :-
agriculture (include aquaculture);
ship port and yard;
2. Cabinet resolution on 23 July 1991. This resolution was intended to stop the destruction of the mangrove, the essential tenets of the resolution are:-
To restrain any projects which will change the condition of the mangrove and which will not benefit the country economically and socially.
To examine the issue of land use in mangrove and confiscation of documents which do not follow forestry law.
To retract all land use documents in mangrove and change to apply with the right to earn a living or leasing.
To move the rural poor, who earn their living in mangrove, into Economic Zone B and apply forestry community methods for management practices.
To set the area of mangrove for personal holding.
To set the land use plan for industry and coastal aquaculture so that coastal ecology can be conserved, and also to provide a water supply system in the area beyond the mangrove.
To disseminate conservation knowledge to local people.
To support mapping of the mangrove that reflects the real situation.
To allow the National Bank of Thailand to administer the provision of commercial bank projects which convert the mangrove.
4.1.3 Priorities for research on the improvement of shrimp farming
To maintain the sustainability of shrimp farming. The renovation of failed shrimp farms in the provinces of Bangkok, Samut Prakarn, Samut Sakorn, Samut Songkram and Petchaburi, by improvement of farm management, has been achieved. The Samut Sakorn Coastal Aquaculture Centre has been conducting trials by treating inflow water before it is used for filling the shrimp ponds. A water storage pond is constructed and the area of pond must be equal to the area of cultivated ponds. The drainage water will be pumped into the storage pond and kept for a one month period to allow for chemical recovery. The water is then chlorinated using 10 ppm chlorine over a one week period. When it is assured that the water is free from chlorine, that water is used to top up the culture ponds at a rate of 10% rate. The water is of such good quality in the culture pond that it will not be drained out through the whole period of rearing. Stocking densities are 20 pieces per m2 with a pond water depth of 1.25 m. Within 4–5 months, the 1 rai of pond will yield 600 kg or 3.750 t/ha. This is a promising methodology to ensure the sustainability of shrimp farming practices in Thailand.
The Department of Fisheries is formulating a project to renovate the failed shrimp farms by applying techniques of water treatment and recycling.
Private sector. After the collapse of shrimp farms in the Inner Gulf of Thailand, shrimp farmers have been made aware of environmental problems. Some of these farmers moved their farms to the Andaman Coast (Indian Ocean). The construction of the new farms was done in the rice field beyond the mangrove. More attention is now paid to official recommendations and instruction are followed.
6. CONCLUSIONS AND RECOMMENDATIONS
Marine shrimp culture along the coast is one of the main economic activities in the country. Shrimp farming provides employment and earns national income. However, if the shrimp farmers do not know how to apply proper management, the coastal environment may be damaged through the destruction of mangrove and their own culture practices may be adversely affected. Governments should promote the development of marine shrimp culture along the coast but before implementation, a development plan should be formulated and good management practices should be specified, which should include:-
A land use plan should be formulated which does not allow the utilisation of mangrove for shrimp culture. The most suitable area for shrimp farming is rice fields or unused low land beyond the mangrove. The level of such land will be not over 1–2 m above the high tide level.
To provide infrastructure which supports the shrimp culture industry such as drainage canals, roads, electricity and other necessary services. To facilitate the common use of those infrastructures, the structure of farm plans should be designed as a closed group of farms.
Control and enforcement of farm practices and the number of farms will be done by the official agency.
To provide education on farm and water management to farm owners and farm operators before they start farming. Visits of government extension officers and shrimp farming scientists will be made frequently.
Monitoring of sea water quality along the coast will be routinely conducted and information on water quality transferred to the farmers. Shrimp pond wastes will not be discharged directly into natural water ways. The waste treatment pond will be attached to the farm system and waste must be treated before discharge.
Research on farm management, disease and parasite problems must be conducted and findings regularly transferred to the farmers.
Dr. Pham Thuoc, Research Institute of Marine Products, Hai Phong.
Cage culture of marine finfish in Hai Long Bay.
This report gives details of the relationship between aquaculture and the environment in Vietnam. It gives information on aquatic resources in Vietnam, environmental problems related to aquaculture and recommendations for confronting some of the major problems identified.
In recent years, especially in the Indo-Pacific region (including China, Japan, Taiwan, Hong Kong, Thailand, Philippines, Indonesia, Singapore), aquaculture has been developing rapidly, both on a large and small scale. Aquaculture in Vietnam has existed for quite a long time, and is characterised by diversity and self-reliance. The development of aquaculture is based on the experience of rural people and the available natural resources, resulting in differences in culture practices in the northern, central and southern parts of the country. Aquaculture production comes from collective and individual activities. State and public institutions only control about 10% of waters areas, and these are mostly large water bodies where aquatic productivity is quite low. Aquaculture has been developing rapidly in Vietnam recently, particularly the culture of fish and shrimp for export, stimulated by increasing interest among the rural population.
Capture fisheries and aquaculture in Vietnam has to supply approximately a half of the animal protein for the population. Aquaculture production currently contributes about 30–40% of the total fishery production. In addition, aquaculture offers scope for employment in production and associated industries (such as processing and feed supply) thus making a contribution to increasing the living standards of the people. The development of aquaculture in Vietnam is based on the ecological systems of the country, for instance, mangrove and coral ecosystems and littoral and estuarine environments. Hydrological factors, climate and geography (including the effects of human beings) also play a role in the development of aquaculture. If targets are met, by 1995 aquaculture production in freshwater, brackishwater and marine environments will have reached 400,000 tonnes. This includes provision for domestic consumption and export requirements. To achieve this production level, however, attention will need to be given to efficient utilisation of water bodies, preservation of the aquatic environment and sustainable use of natural ecological systems. The problems of environmental conservation are becoming increasingly acute as exploitation and aquaculture are developing at a rapid rate and pollution problems are becoming more serious.
Map of Vietnam.
Since the mid-seventies, an environmental emphasis has been put in State plans, thousand of hectares of forests and mangrove forests have been replanted and regulations concerning environmental preservation as well as resource management have been promulgated. There is an increasing emphasis on information exchange and education of the people on environmental conservation. Marine and inland water pollution will become an increasingly serious matter for fisheries ecology and resources. The Government has given special attention to the influence of the environment on fisheries and aquaculture, however, environmental deterioration has had a serious effect on fisheries and will become increasingly important in the future. The reasons for such environmental deterioration are war, over-exploitation of natural resources, lack of technology and increasing population pressures. There is a growing awareness among people in the country concerning environmental protection, however, there is still a need to increase efforts to improve environmental protection for fisheries and aquaculture resources.
This country report gives information on the interactions between aquaculture and the environment in Vietnam. It includes a broad review of the environmental issues involved in aquaculture development, a more detailed “case study” of the environmental aspects of coastal aquaculture development in Vietnam and recommendations for the improved environmental management of future aquaculture development within the country.
3. STATUS OF AQUATIC RESOURCES AND AQUACULTURE
3.1 Aquatic resources in Vietnam
3.1.1 Coastal resources
Vietnam has 3,260 km of sea coast. The economic exclusive zone (EEZ) is about 1 million km2, there are more than 4,000 large and small islands and a complicated topography. In coastal areas, there are lagoons, open coasts, gulfs, and ponds. There were around 250,000 ha of mangrove forests in 1983 and there are around 100,000 ha of lagoon and closed gulfs, and 290,000 ha of muddy littoral areas. There are a large number of rivers entering coastal waters, with around one big river mouth each 20 km of the coast (112 rivers mouths). The Vietnamese sea waters are situated in the intertropical region and its climate is governed by a monsoonal regime. There are a wide range of environmental conditions along the long coastline. Table 1 gives a brief description of the physical environment along the coast of Vietnam. In general, the coastal areas and inland waters of Vietnam can be divided into three different regions: northern, central and southern. The natural character of the marine and brackish waters are strongly influenced by two large river systems; the Red river in the north and the Mekong river in the south.
Table 1. Features of the major coastal environments in Vietnam.
|Quang Ninh to Thanh Hoa.||Shallow coastal plain; salinity intrusion inland common; 20–30 ppt inland common; semi-diurnal tide; amplitude 3–4m.|
|Nghe An to Da Nang.||Steeper coastline; salinity 20 ppt in coastal lagoons; daily tide not uniform; tidal amplitude 1.5–2m.|
|Da Nang to Ba Lang An (Quang Ngai province).||River slope rising; salinity varies over short distances; daily tide not uniform; tidal amplitude 1.5–2m.|
|Ba Lang to Cam Ranh Bay (Khanh Hoa province).||Small coastal plain; salinity 31 ppt; daily tide not uniform; tidal amplitude 1.5–2m.|
|Cam Ranh Bay to Vung Tau.||Transitory area; salinity decreasing at 30–32 ppt; in estuaries salinity is 20–30 ppt.|
|South of Vung Tau and Mekong delta.||Extensive coastal plain; Eastern coast; daily tide not uniform; tidal amplitude 3–4 m; Western coast; diurnal tide; tidal amplitude 1 m.|
The Red river delta area belongs to the Southeast Asian monsoon tropical region, affected by two main monsoon systems: the north-east monsoon from October to March, which is a cold, dry and foggy season; and the south west monsoon from April to September, which is a wet, hot and typhoon season. Depending on the geological position and topography of each region, the fluctuation of the monsoon appears differently. In addition, the region suffers from typhoons originating in the West-Pacific. Annually, there are about 4–5 typhoons or tropical low pressures formed in the Eastern Sea.
The typhoon season is usually from June to the end of October, although in some years, early typhoons and tropical low pressures may occur in February and the season may last until December.
The distribution of the number of typhoons and tropical low pressures formed in the East Sea is shown in Table 2.
Table 2. Number of typhoons in the Eastern Sea according to month (1950–1975).
|Number of typhoons||0||1||0||2||6||19||16||34||24||15||9||3||128|
In the Red river delta, there is a strong influence from the north east monsoon. Typhoons appear in this area in May and terminate in October-November. The tide in this region is a simple diurnal tide. In winter, water temperatures range from 16–20°C, the lowest temperature is 14°C. In summer, the water temperature is from 27–29°C. The salinity pattern in the estuaries is:
Dry season (December to March). In this period the quantity of freshwater entering the sea is less and the fluctuation of seawater is positive. Salinities are relatively high and stable, from 20–31 ppt.
Rainy season (May to October). In this period, the quantity of freshwater entering the sea where the survey is carried out is great. The fresh water quantity is positive therefore the salinity is usually low and highly variable.
Other characteristics of the coastal environment in the Red river delta are noted in Table 3.
Table 3. Characteristics of the coastal environment in the Red river delta.
|Tide||The area of Haiphong has uniform daily tidal with mean tidal amplitude of 2.6–3.6m.|
|pH||In general, Haiphong waters are weakly alkaline with pH 7.8–8.35. The distribution and variation of pH values are controlled by hydrographic conditions of the estuaries. In the dry season, pH is higher and more stable, about 8.00–8.35. In the rainy season, pH is lower, about 7.80–8.20.|
|Nutrients||Phosphate content in water off Haiphong is relatively low, about 3.5–5.0 mg P/m3. Lower than water in the Tonking Gulf.|
|Dissolved oxygen||The variation off Haiphong is not great, about 4.5–5.5 ml/l. Dissolved oxygen saturation (O2%) is about 90–110%.|
|Zooplankton and benthos||167 species of zooplankton (100,000 pcs - 1,000,000 pcs per cubic meter), averaging 240 mg/m3 in water. 31 species of benthos recorded.|
|Phytoplankton||183 species of phytoplankton recorded in Haiphong area, 127 species from brackish water ponds (of these silicic algae make up 80% of the total).|
The lagoons in the Central region of Vietnam are typical of those in the coastal provinces. Tam Giang, Cau Hai and Lang Co lagoons spread 60 kilometers along the coast of Quang Binh, Quang Tri and Thua Thien provinces. The rivers here are short with mountains reaching down close to the sea. As a result, the salinity is high in the dry season. In Quang Binh province and Thua Thien Hue province there is a large amount of water in flood season, with salinity of 5–7 ppt and in the dry season salinity is 16–28 ppt. Table 4 gives some further details of the coastline in the central region.
Table 4. Characteristics of the coastal environment in the central region of Vietnam.
|Tide||Mostly a mixed type consisting of diurnal and semi-diurnal tide, but irregular. There are about 18–20 days of diurnal tide per month. In Thuan Hai province there is a semi-diurnal tide. The tidal amplitude is 0.7–1.2 m.|
|pH||pH is 7.0–8.2, depending on season.|
|Zooplankton||34 species of zooplankton, 450–730 ind/m3. In general, the number of organisms is relatively poor because in rainy season water flows strongly in lagoons and in dry season it is not fertile.|
|Phytoplankton||153 species of phytoplankton recorded, density is 290–8,000 individuals per one cubic meter. Silica algae make up 67–75 % of the total.|
The central region is affected by typhoons. According to statistics, typhoons and tropical low pressures come directly into the central part of Vietnam. Annually there are on average 4.4 typhoons and low pressure in this region. Besides heavy rains and floods, typhoons and low pressures also cause seawaters to rise and serious saline intrusion into inland areas.
The Mekong river delta is a major economic region, with a productive capture fishery and aquaculture industry. In this area, the influence of the north-east monsoon is decreasing, but the south-west monsoon has a major influence. The north-east monsoon starts from the end of October and ends in the middle of March. The south-west monsoon is from April to September. In the Mekong river delta, there is almost no typhoon. The annual variation in temperature is from 26– 28°C. In the estuaries, salinity fluctuates from 22–32 ppt with a pH of 6.5–7.5. There is a heavy load of silt from the Mekong river. Mangrove forests along the coastal area contribute another 5 t/ha/yr of decomposing leaf litter (Hong, 1983). The Mekong river delta is highly suitable for mangrove forests, particularly in the southern part of the delta in Minh Hai province. However, these forests have been seriously degraded, partly by war, and more recently by over-exploitation for aquaculture and wood. The coastal area is starting to be polluted in some areas due to agricultural and other wastes. The area is also subject to increasing human pressures because of migration.
In the Mekong delta, the environmental character in the east is different from that in the west. For example, in An Ninh, An Bien districts in Kien Giang province (on the west), the salinity is 23–27 ppt and the pH is 8.5–8.7 in dry season, but in rainy season the salinity is 2.3–4.8 ppt and pH is 6.9–7.0. In Ba Tri district of Ben Tre province (on the east), the salinity recorded is 25.8 ppt and the pH is 7.5– 8.4 in the dry season, but in rainy season the salinity is only 18.6 ppt and pH is 7.4 (Luu, 1991).
3.1.2 Inland resources
There are estimated to be around 1.4 million ha of inland open waters in Vietnam including a large network of rivers, with at least 2,345 rivers of length greater than 10 km long. The total length of the main inland waterways is about 2,500 km in the north (mainly the Red river system) and 4,500 km in the south (mainly the Mekong river system). The main rivers of Vietnam are the Red and the Mekong rivers, their lower basins resulting in two vast alluvial plains. In the north, the Red and Thai Binh river basins have a combined area of 14,700 km2. The Red river flow ranges from 1,000 m3/s in January to 13,000 m3/s in July and the waters are very turbid with high sediment loads. On the central Vietnam coast with mountainous terrain, the rivers have short courses and are often torrential. The maximum flows in these rivers coincide with the rainfall peaks in October-November. The southern Mekong river has an annual discharge averaging 14,800 m3/s with a peak of 40,000 to 50,000 m3/s in September. Water turbidities are lower than in the Red river but the large volume of water discharges between 70 and 100 million tonnes of sediment into the Eastern Sea each year.
In general, the quality of water in the rivers is good. In estuarine areas, there are wide seasonal variations in salinity. In the Red river basin, in the northern part of the country, the highest salinity is found between July and August. In the Mekong delta, the highest salinity is in March and April and the lowest in September and October. The physical character of water of the Red river is monitored at 5 research stations: pH varies from 7.2–7.8, turbidity is high at 377–415 NTU, water conductivity is 18.7–21.5 μS (mean value 19.9). The Red river possesses high turbidity, contains a lot of alluvium and the content of the mixture substrate is high. pH and water conductivity of the river are average and suitable for aquatic life. The average rainfall in the freshwater areas of northern Vietnam is 1,500–2,000 mm, with 80–85 % of rain concentrated in the flood season from April to October. In the dry season, many lakes, ponds, streams and rice fields are dry. The temperature in the following water is fairly stable, in mountainous regions it is 16–26°C and in the lower deltas it is 17–22°C. The concentrations of nitrogen and phosphorus compounds tends to increase downstream. pH in agricultural low land areas is 5.2–6.6, and in alluvial plains pH is 7.3–8.3.
In the southern part of Vietnam, the Mekong river delta is situated in the tropical monsoon region and hot or warm throughout the year. The annual variation in temperature is not small. The mean temperature is 27.3°C, with a maximum of 30°C and the coldest temperature not under 20°C. In the main river systems, the dry season pH is from 7.8–9.5 and in the rainy season it is 7.0–7.5. In general, the freshwaters of the Mekong have great advantages for aquaculture development, due to the favourable warm and wet climate and lack of typhoon. The major rivers in the Mekong delta are the Mekong and Bassac rivers. Many of the surrounding areas are covered by water in the rainy season. In rivers, the turbidity varies from 19 to 35 cm depending on different seasons. The water is fairly clean and in general not too polluted (Table 5). Compared with other rivers in Vietnam, the Mekong river region is particularly diverse. There are 254 species of phytoplankton, 49 species of zooplankton and 47 species of benthos. Biomass is also high: phytoplankton is 29,950–674,670 individuals/litre, zooplankton is 885–8,662 individuals/m3 and benthos is 3.5–25.8 g/m2 (Luu, 1991).
Table 5. Water quality in the Mekong River.
|HCO3-||74.0 to 106.8 mg/l|
|Dissolved oxygen||4.5–7.5 mg/l|
|Carbon dioxide||3.8–4.7 mg/l|
Apart from the rivers, lakes and man-made reservoirs are found in several parts of the country. The total area is estimated as 164,000 ha, but in the future there may be 1,003,638 ha taking into account expansion of reservoir area.
3.2 Aquaculture production
Aquaculture in Vietnam is carried out in inland and coastal environments and a wide range of animals and plants are cultured. A list of cultured freshwater fish is given in Table 6 and the total present and future area is given in Table 7.
Aquaculture in Vietnam can be summarised as follows:
Coastal aquaculture in lagoons and ponds: Recently, due to the export of shrimp and seaweed, brackish water culture has brought higher economic returns and has developed more quickly. There has also been some interest in marine cage culture recently.
Aquaculture in large inland bodies/water surfaces: Utilising natural as well as artificial seeds, production tends to be low.
Aquaculture in small lakes and ponds: The areas used only take about 10% of the total area, the yield is relatively high and production contributes around 60% to total aquaculture production.
Cage culture, in inland waters and coastal seas.
Aquaculture in rice fields.
Table 6. Freshwater fish cultured in Vietnam (12 local species; 11 imported species).
|Scientific Name||Culture methods|
|1. A. Local Species|
|2. Pangasius hypophthalmus||Ponds, lakes|
|3. Pangasius sp.||Ponds, lakes|
|4. Puntius altus (Giinter)||Ponds, lakes|
|5. Pangasius nasutus (Bleeker)||Cages|
|6. Puntius schwanenfeldii (Bleeker)||Cages|
|7. P. gonionotus (Bleeker)||Ponds, Cages|
|8. Puntioplites proctozysron (Bleeker)||Ponds|
|9. Lentobarbus hoovenii (Bleeker)||Ponds, Cages|
|10. Fluta alba (Zuiew)||Tanks|
|11. Clarias macrocephalus (Giinther)||Ponds|
|12. Channa micropeltes||Cages|
|13. Trichogaster pectoralis||Low land|
|B. Imported Species|
|1. Cyprinus carpio L.||Ponds|
|2. Hypopthalmichtys molitrix||Ponds, Reservoir|
|3. Hypopthalmichtys nobilis||Ponds, Reservoir|
|4. Ctenopharyngodon idellus||Ponds, Reservoir|
|5. Oreochromis mossambicus (Peters)||Ponds|
|6. Oreochromis niloticus (Peters)||Ponds|
|7. Helostoma temmincki||Ponds|
|8. Osphromeinus goramy (Lacepede)||Ponds|
|9. Clarias gariepinus||Ponds, Tanks|
|10. Micropterus dolomieu (Lacepede)||Lakes|
|11. Hypomesus olidus (Oallas)||Lakes|
Table 7. Potential of water surface areas and cultured production of Vietnam in 1985.
|Area (ha)||% of total||Area (ha)||% of total||tonnes||% of total|
|Large water surface||394,300||28.5||91,215||25.0||0.06||5,473||4.2|
Source: Development schedule for aquaculture, Institute of Fishery Economics and Planning, 1989.
Aquaculture production in Vietnam contributes about 30% to fishery yields for the whole country. It makes an important contribution to exports, particularly for shrimp which accounts for 30–40% of the total products exported followed by seaweeds and invertebrates. Vietnam has systems for producing fish fry and it has been estimated there are at least 375 fry producing stations. There are estimated to be about 215 shrimp fry rearing stations: 6 stations in the north, 190 in the central part and 19 stations in the south and the number is expanding rapidly. However, in inland and coastal waters there is still a heavy reliance on the natural seed supply. Fry and seed supply is a big constraint at the present time. Due to the rapid development of cultured areas, natural seed will not be sufficient to provide the increasing needs for fry. Small-scale private involvement in hatcheries is increasing, especially in the central coastal provinces of Vietnam. Here, private hatcheries currently produce more than 200 million of shrimp post-larvae per year.
Freshwater fish culture is developing, but not in a regular manner. In the northern mountainous provinces, provinces in the Red river delta, Western plain (Tay Nguyen), Hanoi, Ho Chi Minh City and An Giang province, freshwater fish culture has been shown to be economic. However, in other parts of the country, freshwater rearing ponds have low economic returns. Along the coast of Quang Ninh province, a cage farm cultures marine fish in cages in sheltered water. In 1992, fish culture and exploitation in Vietnam met with difficulties, particularly with respect to capital for investment as well as climate. However, the sector has made every effort to gain a production of 1,086,800 tonnes in which fishery exploitation takes more than 730,000 tonnes and aquaculture takes 340,000 tonnes (Table 8). Aquaculture area in 1992 in Vietnam can be shown generally as follows:
|Utilised area||530,000 ha|
|Shrimp and special products coastal culture area||205,000 ha|
|Newly developed area||6,000–7,000 ha|
|Extensive culture changed to semi-intensive.||3,000 ha|
Aquaculture focuses mainly on fish and shrimp culture and also special products cultured for export such as crab, turtle and molluscs. In some localities as Quang Ninh, Thanh Hoa, Thua Thien Hue, Minh Hai, An Giang, aquaculture is developing mainly on an individual basis, combining aquaculture with family economic development, and giving work for labourers. Some state enterprises have co-operated with foreign countries to culture seawater fish species, such as in Quang Ninh, Hai Phong, Quang Nam and Da Nang and these have produced good export commodities. Shrimp culture areas in Vietnam reached 189,000 ha with a yield of around 33,000 tonnes. The mean yield is 182 kg/ha.