Hue University of Sciences
Hue City, Viet Nam
Phap, T.T., and L.T.N.Thuan. 2002. Tam Giang Lagoon aquatic systems health assessment. p. 225-234. In: J.R. Arthur, M.J. Phillips, R.P. Subasinghe, M.B. Reantaso and I.H. MacRae. (eds.) Primary Aquatic Animal Health Care in Rural, Small-scale, Aquaculture Development. FAO Fish. Tech. Pap. No. 406.
Tam Giang Lagoon, one of the largest lagoons in Asia, has an area of 22,000 ha and stretches for more than 60 km. Current aquaculture methods are mainly fish ponds, net enclosures and cage systems. Ponds are more commonly used for extensive, improved-extensive and semi-intensive types of culture, and in 1998, covered an area of about 1,980 ha. Aquaculture is being developed in the lagoon to overcome the depletion of natural aquatic resources and to satisfy the demand of the increasing population for aquatic products. The local government considers it an alternative measure to improve lagoon-dwellers' income and a means of reducing random exploitation of the lagoon's resources. As a consequence of the increased exploitation, environmental conditions have deteriorated. Some water quality parameters have exceeded their permissible limits. Diseases have been reported in four major cultured species (i.e., seaweed (Gracilaria sp.), shrimp, crab and fish) with high risk and frequency. Two disease epidemics broke out in 1995 and 1998, causing great losses to aquaculturists. The diseases resulted in an enhancement of the role played by the Aquatic Animal Hygiene Inspection and Veterinary Office of the Department of Fisheries in developing new mechanisms and strategies for the management of aquatic animal health in the lagoon. This paper also presents a proposal for a "Tam Giang Lagoon Aquatic Systems Health Assessment," which is based on research results from the International Development Research Centre of Canada (IDRC)-sponsored project "Management of Biological Resources in Tam Giang Lagoon," as well as on input provided by specialists from the Network of Aquaculture Centres in Asia-Pacific (NACA).
Tam Giang Lagoon (see Figure 1), which runs along the coast of Thua Thien Hue Province, Vietnam, has an area of 22,000 ha and a length of more than 60 km. On its eastern side, the lagoon is separated from the sea by sandy dunes with two openings, Thuan An and Tu Hien. On the western side of the lagoon are rice fields and river estuaries. The area is unique in terms of landscape and biological resources. Communities settled there to exploit the lagoon's biological resources and farm on the sandy land at its edge.
Because of increasing population pressure and a decrease in aquatic resources, government officials consider aquaculture as an alternative means of improving villagers' income and reducing exploitation pressure on the lagoon. As a result, aquaculture has recently developed so rapidly that it is having a strong impact on attempts to promote a sustainable aquaculture production system in the lagoon area.
Figure 1. Map of Tam Giang Lagoon.
Tam Giang Lagoon mixes with the sea through the two openings on the eastern side. The lagoon also receives water from many rivers, such as the Huong, Bo, Dai, O Lau and Truoi. Thanks to this unique topography, the lagoon has a mixture of fresh and salt water that makes the changes in its salinity both seasonally and spatially regular. This creates a typically brackishwater environment with valuable resources and a high potential for aquaculture.
The average depth of the lagoon is 2 m, although along its length there runs a channel 3 to 4 m deep. Thuan An Estuary is deepest, at more than 7 m. Therefore, the salinity and characteristics are favourable for the construction of aquaculture ponds and net enclosures in most parts of the lagoon.
The first aquaculture activities in Tam Giang Lagoon began with seaweed cultivation in 1977. Shrimp culture began in the early 1990s, and from 1990 to 1993, the area of shrimp ponds increased from 42 to 437 ha. Meanwhile, the area under seaweed cultivation increased from 226 to 357 ha. The total aquaculture area in the lagoon reached 1,000 ha in 1995 (Phap 1996).
Present aquaculture methods involve mainly ponds, net enclosures and cages. Ponds are more common for the following systems: extensive, improved-extensive and semi-intensive. The area of production and the aquaculture patterns in the lagoon in 1996 are presented in Table 1 and Figure 2 (Phap 1996).
Table 1. Types of aquaculture and areas covered in Tam Giang Lagoon.
During the 1998 culture season, the area of net enclosure in Phu Tan Commune alone (where most of the aquaculture activity is concentrated) was 413.5 ha. Although this does not present a full picture of the aquaculture boom in the lagoon, it does reflect the significant rate of increase.
Figure 2. Aquaculture production in Tam Giang Lagoon, 1992-96.
Aquaculture is regarded as a pilot scheme investigating the economic potential for fisheries development in Thua Thien Hue. The Department of Fisheries in Thua Thien Hue promotes semi-intensive culture in which villagers include aquaculture as part of their livelihood portfolio and state-run companies supply seed and technical support. This is the official strategy for aquaculture development in Thua Thien Hue Province (Phap 1996).
In the past five years, basic aquaculture techniques, acquired from training courses held at the Fishery Extension Centre, Phu Tan, have enabled the lagoon fishers to experiment and learn from other experienced aquaculturists. Step by step, they are developing their own aquaculture practices that are characterised by low stocking density and polyculture. Polyculture seems to be more sustainable than monoculture, as it reduces the risk of losing the whole crop due to disease. Common polyculture patterns include: shrimp (Penaeus monodon)/crab (Scylla serrata)/ fish (Siganus guttatus)/seaweed (Gracilaria tenuistipitata); shrimp/ seaweed and shrimp/crab/fish. Grouper and grass carp (Ctenopharyngodon idellus) are cultured in cages.
This flexible approach is more appropriate to the environmental conditions of the Tam Giang ecosystem and to the management and investment capacities of local people. This runs counter to previous aquaculture development (semi-intensive and monoculture) that was applied by state-run companies. Low intensity polyculture has resulted in increased economic benefits, because investments for seed and feed are low, no improved techniques are required, product quality is good and the price obtained for the product is higher than in high-density culture.
Meanwhile, aquaculture companies that relied on more intensive cultivation methods have had to abandon their ponds or rent them to fisherfolk; these companies are no longer involved in aquaculture development in Tam Giang Lagoon. However, aquaculture production in the lagoon is still regarded as unstable, and further research is required to address the associated problems.
Approximately 220,000 people in 38,000 households, or about 20% of the population of the province, live directly around the lagoon. The population is increasing at a rate of 3.1% per year. Families in villages around the edge of the lagoon that depend on agriculture as their main livelihood activity have the lowest income in their community, while families who have adopted aquaculture have higher incomes (Newkirk 1995).
Before 1970, the total fish catch in the lagoon was about 3,600 mt/yr; however, since 1980, production has been around 2,000 mt/yr. The number of persons engaged in fishing has increased rapidly, from 66,000 in 1980 to 90,000 in 1993. The amount of fishing gear used has also increased; 13 types of fishing gear are in use, including fishing corrals, fixed lift nets and bottom nets, all in high density. Electro-fishing gear is also becoming commonplace.
High fishing intensity has resulted in the depletion of the lagoon's resources and increased the difficulties of fisherfolk. To improve the situation, aquaculture has been accepted by the fisherfolk and is considered by local government as an alternative source of income, as well as contributing to reducing degradation of the lagoon's aquatic resources. Aquaculture brings greater income, which helps improve the life of the fisherfolk. For example, in Phu Tan Commune, changes have resulted in an improvement of infrastructure, and most families now have brick houses with modern conveniences. Community health care and education are also improving; the number of malnourished children is decreasing and over 80% of the children attend school.
Nevertheless, aquaculture demands a high initial investment, and a high risk of disease outbreaks may result in losses. Therefore, the poor fisherfolk, who are mostly migratory fishers, cannot get involved, while their natural fishing grounds are becoming more confined This widens the gap between the more wealthy, the mobile fishers and the poor in these communities.
Aquaculture in Tam Giang Lagoon is generally regarded as a risky venture associated with high mortalities from disease. Diseases are common in the lagoon, and all four groups of cultured species (seaweed, shrimp, crab and fish) have been affected.
In 1985 "colourless" disease appeared in Gracilaria. The local fishers call it "white canopy" disease, the tips of the fronds becoming white and the thallus perishing. Meanwhile, some fish species living in the Gracilaria ponds, such as mullets and rabbitfish, suffered from ulcers.
From 1993 to 1994, shrimp diseases began spreading. Initially, the disease affected only limited areas; then, in 1995 and 1997, diseases reached epidemic proportions.
Recently, at the Quang Thai Commune, a research site of the Tam Giang Project,
26 households were supported with capital from the project to develop grasscarp
cage culture; however, after. months of rearing the fish, 80% of the cages suffered
100% mortality from "red spot" disease. So far, 16 diseases of aquatic
animals have been recorded in Tam Giang Lagoon (Table 3).
In the Hue area, there are eight hatcheries for shrimp fry production (one state-run, seven private) and 28 nursing units. The average number of postlarvae (PL15) produced each year is about 20 million, meeting half of the local demand.
The common diseases in fry are luminescent disease, carapace deformation, red spot and external fouling. Interventions applied by fisherfolk to reduce the impact of disease on affected animals consist of changing the water to improve water quality and providing enough food to help the animals overcome the disease. Some fry producers have used antibiotics and chemicals for treatment of disease (Table 4).
Aquatic animal diseases have been recognised since 1994. They tend to spread over a large area of the lagoon in March, April, July and August of each year. There are no official statistics on the economic impact of disease; however, data from the Department of Fisheries suggest that the impact has been severe. For example, during the 1995 shrimp disease epidemic, 300 million fry and 900 million grow-out animals died. This resulted in huge capital losses for the farmers, and many have been unable to repay their bank loans. A survey showed that one household lost all its capital when it invested 38 million Vietnamese Dong (VND) (1 US$= 14,000 VND) after stocking 20,000 PL15 in a 5,000 m2 pond in 1998. Due to disease, another household received only 15 million VND in returns after investing 52 million in a 3,000 m2 pond (Anon. 1999).
The Aquatic Animal Health Inspection Office (AAHIO), Department of Fisheries, has responsibility for managing the health of cultured species in the whole lagoon. The staff of the AAHIO consists of five people, one of whom is responsible for carrying out laboratory work. The other staff conduct monthly field visits to inspect the health of cultured animals, to provide the fisherfolk with guidance to improve pond conditions before stocking, and to teach them the basic indicators used to identify healthy fry. The AAHIO keeps in regular touch with the fisherfolk to assess aquaculture activities and to collect samples of diseased animals.
Fry production is strictly controlled by the AAHIO. All production units require health certificates and production licenses. The AAHIO also organises training courses to teach the fisherfolk how to protect their cultured animals from becoming infected (Anon. 1999).
Table 3. Common diseases of aquatic animals and plants in Tam Giang Lagoon (source: fisherfolk and staff of the Aquatic Animal Health Inspection Office; Anh and Thanh 1998).
Table 4. Antibiotics and chemicals used in treatment of fry diseases (source: producers).
In the event of an epidemic, the AAHIO must report the situation and the resulting losses to the Provincial Peoples Committee (PPC). Based on this report, the chairman of the PPC provides advice and recommends solutions to manage the problem, and provides support to producers who suffer great losses. For example, in the epidemics of 1995 and 1997, the banks extended repayment deadlines and granted low-interest loans (Anon. 1999).
Research on aquatic animal diseases is a new area for the University of Hue and the AAHIO. Initial research conducted by the Department of Biology (Hue University of Sciences) and the Department of Fishery (Hue Agriculture and Forestry) concentrated only on diseases caused by protozoan parasites and fungi, such as Fusarium spp. and Lagenidium spp.
Even though a co-operative programme is in place between the Department of Fisheries and Hue University to study aquatic animal diseases, there are still no effective measures for controlling diseases in aquaculture. Therefore, the office has adopted the following animal health management (Anon. 1999):
One of the objectives of the Tam Giang Project is to develop methods of sustainable aquaculture production by addressing technological, organisational and regulatory issues (Newkirk 1995). From 1998 to 1999, the IDRC-supported Tam Giang Project undertook two research activities, implemented at Phu Tan Commune, related to improvement of the culture pond water of the lagoon: (i) trials on raising monosex Tilapia in polluted ponds, and (ii) a study of preliminary impacts of improved-extensive culture on the natural environment of the pond. Initial results show that:
Tam Giang Lagoon has a close relationship with the sea and the land. Its biological and physical characteristics have created a unique brackishwater ecosystem with a diverse range of resources, supporting a large population around the lagoon.
With rapid development, the whole area over 2 m in depth will soon become an aquaculture area, and this will increase the income of the local people, contributing to poverty alleviation in lagoon fishing communities. However, three main constraints have been identified: lack of capital, lack of good fry and occurrence of disease. The latter is considered to be the biggest constraint, for which there is still no solution. In order to solve this problem, the "Tam Giang Lagoon Aquatic System Health Assessment Project" has been proposed. The specific objectives of the project are:
To identify and assess current problems, the aquaculture production systems in two different areas of the lagoon will be investigated, as well as the range of people involved in using these systems for their livelihoods. The areas are: Phu Tan, where aquaculture is well developed, and Quang Thai, where the people are poorer and aquaculture is a recent introduction. The species cultured, number of households involved and disease problems encountered are shown in Table 5.
Table 5. Aquaculture systems practised in Phu Tan and Quang Thai areas of Tam Giang Lagoon.
This comparative analysis between people and locations, where aquaculture is in different stages of development, will enable lessons from areas with more experienced farmers to be applied in new locations.
The survey will be undertaken by a research team from the Tam Giang Project:
- 7 people from the project
- Provincial Department of Fisheries (2)
- Science University
- Agriculture University
- 4 people (2 from each commune-Phu Tan and Quang Thai).
The survey will use a participatory approach:
Prompt or list of key points.
Train farmers to fill in the key points.
Based on key informant interviews, if the farmers find a disease problem, then researchers will visit the site, observe the situation and carry out field-environmental and laboratory investigations.
Preliminary key points to be addressed include:
An institutional analysis will be carried out to determine the different institutions involved and their current and possible future roles in aquatic animal health management, as well as the training needs at the different levels (village, commune, district and province). Extension capabilities and the support available to farmers will also be evaluated. The roles and inputs of suppliers of seed and bankers as possible sources of management intervention will also be defined.
The outcome from this work is expected to include:
Anh, P., and T.N.N. Thanh. 1998. Occurrence of diseases of Penaeus monodon in the semi-intensive ponds at Quang An District, Thua Thien Hue Province. J. Biol. 20: 93-96.
Anon. 1999. Management of aquatic fry. Annual Report. Aquatic Animal Health Inspection Office, 10 p. (In Vietnamese).
Hong, V.T. 1999. Trials on raising monosex tilapia in polluted ponds in Phu Tan Commune, Phu Vang District. p. 8-16. In: Annual Report of the Project Management of Biological Resources in Tam Giang Lagoon.
Newkirk, G. 1995. Management of biological resources in Tam Giang-Cau Hai lagoon system, Thua Thien Hue Province, Vietnam. Out of the Shell, 5 (1): 1-5.
Phap, T.T. 1996. Development of aquaculture in Tam Giang Lagoon. Thua Thien-Hue,
Viet Nam. 5 p. In: Annual Report of the Management of Biological Resources
in Tam Giang Lagoon Project to the International Development Research Centre