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Shrimp Farming in Sri Lanka: Health Management
and Environmental Considerations

P.K.M. Wijegoonawardena and P.P.G.S.N. Siriwardena

National Aquatic Resources Agency, Colombo 15, Sri Lanka

Wijegoonawardena, P.K.M., and P.P.G.S.N. Siriwardena, 1996. Shrimp farming in Sri Lanka: health management and environmental considerations. In Health Management in Asian Aquaculture. Proceedings of the Regional Expert Consultation on Aquaculture Health Management in Asia and the Pacific. R.P. Subasinghe, J.R. Arthur & M. Shariff (eds.), p. 127–139. FAO Fisheries Technical Paper No. 360, Rome, FAO. 142p.

Abstract

Aquaculture is a recent activity in Sri Lanka. However, farming of penaeid shrimp, Penaeus monodon, has been a successful and lucrative venture until major disease outbreaks occured in late 1980s. Although the main cause for these outbreaks is considered to be the introduction of an exotic viral pathogen, uncontrolled proliferation of farm operations and related aquatic environmental implications appear to have made a direct contribution. This paper describes the status of shrimp farming in Sri Lanka, with special reference to health and environmental issues which prevail in the sector.

INTRODUCTION

Sri Lanka does not have a tradition of aquaculture practice; there was virtually no aquaculture until the begining of the 1980s. Interest in brackishwater aquaculture was generated with the establishment of the Brackish Water Fisheries Station in Negombo as a research and demonstration center. In 1968, the Ceylon Fisheries Corporation constructed ponds on a 20 ha tidal flat, but abandoned them in 1970 after the dikes were washed away. In 1977, a small shrimp farm covering 0.7 ha began operations in the shallow edge of the Batticoloa Lagoon, but had to be abandoned without further production due to civil unrest in the country.

Until the mid-1960s, the shrimp fishery was entirely a lagoon and estuarine by-catch fishery. With the demand in the international market continuously rising, trawling at sea for shrimp developed rapidly and production from this capture fishery reached a peak of around 4 000 metric tonnes (mt) in the 1980s (Siriwardena, 1989 - unpubl. doc.). With the problems associated with civil disturbances in the north and east, fishing there was suspended, while trawling in the western and northwestern coasts showed signs of depleting the shrimp resources. Given the importance of increasing shrimp production and the availability of unpolluted brackish water and land suitable for shrimp culture that is essentially unsuitable for agriculture purposes, the Government of Sri Lanka promoted private sector investments in shrimp farming by offering various incentives. In response to the high demand in the world market and ever-increasing export prices, local and multinational companies and small-scale entrepreneurs embarked on shrimp farming. Over the last decade there has been a rapid development of shrimp farms in the northwestern province of Sri Lanka, but this has been accompanied by environmental and disease problems which have led to the closing of some farms and loss of productivity in others.

Shrimp culture operations are entirely in the hands of private sector entrepreneurs who use local labor and, partly, expatriate technicians. Large areas of land adjacent to lagoons have been utilized for shrimp culture, which developed rapidly on the western and northwestern coasts in the mid-1980s. Operations along the east coast ceased after the 1983 civil disturbances. To date, more than 300 entrepreneurs have undertaken shrimp farming, and a total land area of more than 2 000 ha has been utilized in the northwestern and western coastal areas for the development of shrimp farms.

Apart from commercial-scale pond farming of shrimps, experimental shrimp culture in pens was attempted in 1986. Trials were carried out in Chilaw and Negombo lagoons and production levels of 400 to 600 kg/ha/crop of Penaeus monodon and P. merguiensis were achieved on a semi-intensive scale of practice.

COASTAL RESOURCES FOR SHRIMP CULTURE

The coast of Sri Lanka is endowed with large areas of saltwater lagoons, estuaries, mangroves, and coastal mud flats. Thirteen of the 24 administrative districts in Sri Lanka have maritime boundaries and, the development of coastal aquaculture is therefore restricted to these districts. The extent of water area suitable for coastal aquaculture in pens is estimated to be around 12 000 ha (Weerakoon and Siriwardena, 1988). The water area for the development of cage culture in brackish water is negligible (Siriwardena, 1982), since areas deeper than 2 m are restricted to the navigational paths of most lagoons. There is about 6 000 ha of land suitable for shrimp farming in Sri Lanka, of which around 57% and 20% are situated along the northeast and northwestern coastal areas (Samaranayake, 1986). The National Aquatic Resources Agency (NARA) of Sri Lanka has identified land areas of 1 200 ha and 250 ha as suitable sites for shrimp farming in the northwestern and southern coastal areas, respectively (NARA, 1989).

SHRIMP CULTURE PRACTICES AND PRODUCTION

Share of shrimp aquaculture in the fisheries sector

The fishery sector is an important part of Sri Lanka's economy and contributed around 2.2% of GDP in 1993. Fish is the most important source of animal protein consumed in the country, about 60% of the population depending solely on fish for their protein requirement, and accounting for nearly 65% of the total animal protein consumed. The steady growth in local production and increased fish imports led to a rapid increase in per caput supplies from 10.7 kg in 1977 to 16.9 in 1989. The bulk of this production came from the coastal marine fishery where in some areas there has been over-exploitation. Inland fish production is heavily dependent on capture fisheries in the reservoirs and tanks. The marine offshore/deepsea fishery is at present more or less confined to the western and southern coasts and has shown a steady growth from an estimated 3 000 mt in 1978 to 33 000 mt in 1993. The sector employs around 150 000 in fishing, supporting a fishing population of about 600 000. In addition, around 13 500 fishermen were involved in inland fishing and another 50 000 are estimated to be engaged in supporting activities, including fish processing and marketing. Employment in fishing represents about 1.75% of total employment, and about 4% of agricultural employment. When ancillary activities are also considered, the respective shares amount to about 2.5 and 5%.

The contribution of shrimp aquaculture production to the total fish production increased from 0.06% (100 mt) to 0.7% (1200 mt) between 1985 and 1993. It has created more than 4 000 jobs, or around 2.0% of fisheries sector employment.

Growth of the shrimp culture industry

Interest in brackishwater shrimp culture in Sri Lanka started in 1977, but the commercial production first entered the market in 1984. In 1984, only one multinational company was producing brackishwater shrimp for the export market. The number of operational establishments had risen to 52 in 1989 and by the end of 1994, the number of authorized farms had increased to 250. The total number of farms including unauthorized farms far exceeds this number.

The water area under culture (excluding bunds) increased from 3 to 12 ha from 1984 to 1986). Due to the expansion of semi-intensive culture practice, the water area under culture increased rapidly in 1997 to 125 ha. By 1989 the area under culture had increased to 243 ha; since then, no proper records have been maintained. The area allocated, however, for authorized shrimp farms amounted to 1 400 ha at the end of 1994. Once again, the total area developed, including unauthorized farms, far exceeds this total and is distributed along the northwestern coastal belt. The estimated employment generated through shrimp farming was over 4 000 at the end of 1994.

Shrimp culture practices

Thirty-one species of shrimp have been recorded from Sri Lankan waters. Of these, only the penacid shrimps have commercial value (de Bruin, 1970). The operational shrimp farms in Sri Lanka practice monostock monoculture of Penaeus monodon (black tiger shrimp), a species which has been selected for culture due to its large size, fast growth, high price, high market potential and the availability of technology (Siriwardena, 1990 - unpubl. doc.).

The shrimp farming industry in Sri Lanka is dependent entirely on hatchery-bred-post-larvae. The present requirement of hatchery-bred post-larvac is around 450 million per year, while the present hatchery production is very inadequate, being around 200 million post-larvae per year (Siriwardena, 1990 - unpubl. doc.).

Culture practice in the mid-1980s was largely intensive; however, this trend changed after the disease outbreak in 1988/89. The farmers who were committed to intensive culture used reduced stocking densities and two crops per year, thereby allowing time for treatment. In late 1989, only seven of 52 establishments were practicing intensive culture (Siriwardena, 1990 - unpubl. doc.). The production rates for intensive and semi-intensive culture ranged between 0–15 and 6–8 mt/ha/yr, respectively. The present trend is to practice semi-intensive culture employing a stocking rate of 15–20 post-larvae/m2 with aeration and artificial feeding.

Of the three sizes of shrimp farm, the small sector comprises the largest number. These farms are viable, and their numbers are expected to increase because of government policy not to permit the existing large farms to become larger and not to approve any more large-scale shrimp farms (Joseph, 1993).

Shrimp culture production

Government plans

Shrimp and finfish culture is being accorded high priority in the National Fisheries Development Plan for 1995 to 2000. Production of cultured shrimp is projected to increase to 5 500 mt, from the present production of 1 200 mt (wet weight).

Shrimp culture production and exports

Shrimp comprises the largest quantity of any export product in the fisheries sector and earns the highest foreign exchange. The percentage contribution of shrimp to the total value of all aquatic products exported varied between 48.5% and 70.3% between 1985 to 1992. The decline in production in relation to the water area under culture can be attributed to the progressive deterioration of the pond environment due to intensive culture and conversion to semi-intensive culture. The contribution of cultured shrimp to total shrimp exports in terms of quantity and value increased from 1985 to 1993, as a capture fishery did not take place in the north and east due to civil disturbances.

HEALTH AND ENVIRONMENTAL CONSIDERATIONS

Health and environmental cocerns have become major issues in many countries where aquaculture has developed to a commercial scale. These concerns include disease outbreaks, effluent discharge, use of antibiotics, habitat change and damage, and the adverse effects of pollutants on the aquatic environment.

Problems related to health management

The first disease outbreak which significantly affected production occurred during 1988 to 1989. The following disease signs were observed (Jayasinghe, 1995):

A drop in production from 5.3 to 1.9 mt/ha/cycle causing an average reduction of 64% in production and an estimated total loss of 186.62 Rs. million (US$ 4.44 million) was observed due to this disease outbreak (Jayasinghe, 1995).

No proper monitoring program for health management and disease has been undertaken since the inception of this industry. Hence, estimation of losses due to disease in terms of reductions in quantity and value is difficult. Brown and black gill conditions and MBV virus were reported in grow-out facilities. Iron hydroxide deposits, hypertrophic changes and hemolytic infiltrations were found among gill lamellae, plus infestations by the ectocommensal protozoan Zoothamnium (Jayasinghe, 1995; Wijegoonawardena, unpubl. data).

Total bacterial counts of 2.4 × 104 to 9.0 × 105 and 5 × 102 to 8.8 × 103 were reported for cultured shrimp and grow-out pond water, respectively (Fonseka and Hettiarachchi, 1991). Of this, 19.4% and 5% were Vibrio and Pseudomonas, respectively. These bacterial counts, however, were made for post-harvest technological purposes and it is difficult to make any inferences on the influence of these bacterial levels during culture.

Luminescent vibriosis has been recently recognized as the most serious disease affecting hatchery production of P. monodon. Luminescent strains of Vibrio species have been implicated in outbreaks of shrimp hatchery bacterial diseases mainly in the northwestern coastal areas of Sri Lanka. The high levels of luminescent vibrios in the sea water of this area may be due to high organic matter, as according to Shilo and Yetinson (1979) these bacteria grow very well in eutrophic sea water. According to hatchery operators of this coastal area, water quality parameters such as temperature, salinity, pH, ammonia, nitrate and phosphate have no effect on the occurrence of luminescent vibrios. In other countries, two species, Vibrios harveyi and V. splendidus, have been identified, withV. harveyi being more dominant. Significant larval mortalities associated with luminescent vibriosis caused by V. harveyi and V. splendidus were reported from hatcheries raising P. monodon and P. merguiensis in Indonesia (Sunaryanto and Mariam, 1986) and in the Philippines (Baticados et al., 1990). The strain(s) of Vibrio causing mortalities in hatcheries in Sri Lanka has yet to be determined. In Sri Lanka, vibriosis has been noted to cause up to 100% mortality of P. monodon from zoea and mysis to post-larval stages. This has aggravated the problem of production shortage in shrimp post-larvac, leading to the recent importation of P. monodon post-larvae into the country. Such importations without proper quarantine measures may cause serious disease outbreaks in the shrimp farming industry.

While most disease control programs emphasize the pathogen (e.g., microbial diagnosis, vaccine development and chemotherapeutic treatment), one must not forget that poor water quality and inadequate nutrition are often basic determinants of disease outbreaks (Sindermann and Lightner, 1988). Questions have been raised as to whether the inter-connected lagoon complex between Chilaw and Puttalam can continue to sustain more than 1 200 ha of shrimp ponds. The canal that serves as the main source of brackish water for the farms is apparently polluted and the risk of disease outbreaks is increasing

There is little information on the amounts of different chemotherapeutants used in the shrimp farming industry, but the increase in their use is causing concern, both from human health and the environmental aspects. The commonly use antibiotics are chloramphenicol, oxytetracycline, terramycin and nitrofuran.

Problems related to the environment

In brief, the problems related to the environment in the shrimp farming industry in Sri Lanka arose mainly from over-emphasis on high production, economic viability and foreign income generation without full consideration of the environmental impacts caused by over-crowding of farms. At the inception, there was no proper zoning plan to facilitate development of an environmentally sound industry. Lack of a proper zoning plan for the northwestern and western provincial coastal belts led to many social problems and destruction of ecologically sensitive areas, such as mangroves and mud flats. Moreover, this destruction has not yet been quantified in terms of ecological importance and value.

When approving a particular site, neither the industry as a whole nor the existing farms in the vicinity were taken into consideration. This led to the establishment of farms in a haphazard manner so that the outlets and inlets of individual farms were located in close proximity, inevitably allowing one to obtain the discharged water from the other and leading to health management problems.

The main water sources serving the present shrimp farming industry are Negombo Lagoon, Chilaw Lagoon, Puttalam Lagoon and the canal connecting these three lagoons, the Dutch Canal. According to the renewal rates and quality of water measured in early 1990, the canal, extending from Chilaw to Mundal has the capacity to supply water to a culture area of 242 ha (Siriwardena and Dayaratne, 1990 - unpubl. doc.). Siriwardena and Dayaratne (1990 - unpubl. doc.), recommended improvements to the Dutch Canal in order to enhance the water renewal rate if the shrimp farming industry was to be expanded in the northwestern coastal belt. However, since 1990, the number of shrimp farms has increased rapidly in this area, exceeding the culture area of 242 ha without any improvements in water renewal rates of the Dutch Canal. Many water quality parameters of the Dutch Canal changed due to effluent discharge from shrimp farms (Table 1). Increased suspended solids may cause a further reduction in the volume and renewal rates of water in the Dutch Canal. If the dissolved oxygen depletes, the increased levels of total sulfides may cause environmental stress leading to fish kills. Such fish kills were reported in the Dutch Canal in early 1995. Moreover, reduced growth rates, lower production and disease problems in shrimp may be attributed to the stress caused by the polluted water source.

The present trend in the northwestern coastal belt is to establish shrimp farms in high saline areas (beyond Mundal up to Puttalam and Kalpitiya) due to unavailability of sites in low saline areas (between Chilaw and Mundal) for development. With the intensification of shrimp farming in high saline areas, the use of fresh water by installing tube wells has increased. Establishment of shrimp farms in high saline areas without assessing the adequacy and status of the water table may result in its depletion, leading to land depression. In addition, too much dependence on underground water may result in a much lower water table, which, in turn, may lead to serious competition for fresh water between aquaculture, agriculture, industry and domestic users and to drinking water becoming salty.

The establishment of many small-scale farms without proper environmental assessment led to the destruction of buffer zones between farms and between water fronts and farms and to interference with the irrigation and drainage systems. The latter causes annual flooding in the areas where shrimp farms are developed.

RECOMMENDATIONS

Disease considerations

There is a need for a regular monitoring program to determine the health status and to recommend mitigatory measures to prevent possible disease outbreaks. Lack of proper monitoring makes it difficult to estimate economic losses caused by disease. A monitoring program should emphasize the following:

Due to the polluted nature of the main water sources used for shrimp farming, there is a great possibility for disease to spread throughout the area. Poor design and unplanned localization and siting of farms aggravate the risk, since infection through the water is a major source of disease transmission. Therefore, improvements such as dredging of the Dutch Canal and opening the sea out-falls are recommended to improve the water exchange rates (Siriwardena and Dayaratne, 1990 - unpubl. doc.).

A risk analysis for health and disease management is recommended. The following areas should be examined:

Environmental considerations

There is a need for the Government of Sri Lanka to recognize the important role of aquaculture in its national economy, so that proper laws and regulations beneficial to its controlled expansion are established. One of the important strategies for the development of shrimp aquaculture is the adoption of transparent policies to avoid the social conflicts and adverse ecological impacts which are currently occuring. Zoning plans, based on scientific investigations and analysis of physical, biological, social and economic information of the areas, especially in the new areas to be developed, would provide a rational approach to the allocation of land and water areas and the development of improved pond designs.

Freshwater resource use must be rationalized. Shrimp farms which are dependent upon fresh water for dilution should not be approved without knowing the availability and adequacy of the natural water table for competitive use without affecting the environment. Prior to approving further shrimp farms in the high saline areas, the following questions should be adequately addressed:

Besides employing the above measures to conserve water resources, construction of water recycling facilities in several demonstration farms to save water and reduce the impact on the environment should be encouraged. Placing a subscribed charge on water pumped from underground would create a water conservation consciousness among farmers.

A “switching over” strategy should be adopted to change the species under culture to a relatively high salinity tolerant species. For example, relatively high salinity tolerant white prawn (Penaeus indicus) could be cultured in high saline areas instead of black tiger prawn, which prefers low saline conditions. This may prevent or minimize the use of fresh water to dilute high saline water in shrimp farms. Moreover, it is generally recognized that high saline species are relatively more disease tolerant than are low saline species. When adopting the “switching over” strategy, the species should be carefully selected, taking into consideration the market trends.

Has cultured shrimp production increased in relation to the increased culture area enough to justify approving a vast number of shrimp farms in the northwestern provincial coastal belt? The production figures show that it has not increased in relation to the increase in culture area. This cannot be totally attributed to the switch over from intensive to semi-intensive practice. It is partly because of the inability of hatchery production to meet the demand and partly because of the slowdown of growth rate of shrimp experienced, probably due to the polluted nature of the water source. Hence, to achieve effective culture, approval of land has to be scaled down, giving due consideration to actual hatchery production and pollution status of the water source.

To reduce the impact of shrimp farming, the “cluster farm” concept may be adopted. Almost all small shrimp farms are being operated without any mitigatory measures, such as the use of oxidation and sedimentation tanks to reduce the hazardous impact on the water source. Depending on the size of the land, the number of such small farms (not exceeding one ha in extent) in a particular area could vary. The “cluster farm” concept may be adopted in the following manner:

This approach would minimize the problem of locating inlets and outlets at close proximity and reduce the sediment and nutrient loading in the water source by utilizing organizing common sedimentation and oxidation tanks.

Adoption of a system to monitor environmental licenses to prevent establishment of unauthorized farms without proper environmental assessments is important.

There was no frequent and proper dialogue between the researcher, the developer and the extensionist. Without proper dialogue, it is difficult to obtain the feedback needed for formulating research to address the problems in the industry. Hence, to establish a proper dialogue between these groups via regular meetings of their representatives is recommended.

REFERENCES2

Anon., 1991. Fish health management in Asia-Pacific. Report on a regional study and workshop on fish disease and fish health management. Asian Development Bank and Network of Aquaculture Centres in Asia-Pacific. ADB Agric. Dep. Rep. Ser. No. 1.

Baticados, M.C.L., C.R. Lavilla-Pitogo, E.R. Cruz-Lacierda, L.D. de la Pena, and N. Sunaz, 1990. Studies on the chemical control of luminous bacteria Vibrio harveyi and V. splendidus isolated from diseased Penaeus monodon larvae and rearing water. Dis. Aquat. Org. 9: 133–139.

de Bruin, 1970. The distribution of penaeid prawns in Ceylon water. Bull. Fish. Res. Stn. Cey. 21: 75–86.

Fonseka, T.S.G., and K. Hettiarachchi, 1991. Incidence of some pathogenic organisms in cultured shrimp (Penaeus monodon) collected from Chilaw. Vidyodaya J. Sci. 3: 23–33.

Jayasinghe, J.M.P.K., 1995. Sri Lanka country report, 357–376 p. In Report on a Regional Study and Workshop on the Environmental Assessment and Management of Aquaculture Development (TCP/RAS/2253). NACA Environment and aquaculture Development Series No. 1. Network of Aquaculture Centres in Asia-Pacific, Bangkok, Thailand, 492 p.

Joeseph, L., 1993. Coastal fisheries and brackish water aquaculture in Sri Lanka. Coastal Resources Management Project of the University of Rhode Island, United States Agency for International Development, 45 p.

NARA, 1989. Identification of suitable sites for shrimp farming: Phase I. North western coastal belt. A consultancy report for Export Development Board and National Development Bank. National Aquatic Resources Agency (NARA), Colombo, Sri Lanka, 291 p.

Samaranayake, R.A.D.B., 1986. Status and prospects for brackishwater aquaculture in Sri Lanka. J. Inl. Fish. (Sri Lanka), 3: 88–90.

Shilo, M. and T. Yetinson, 1979. Physiological characteristics underlying the distribution patterns of luminous bacteria in the Mediterranean Sea and the Gulf of Elat. Appl. Environ. Microbiol. 38: 577–584.

Sindermann, C.J., and D.V. Lightner, 1988. Disease diagnosis and control in North American marine aquaculture. Developments in Aquaculture and Fisheries Science. 17, Elsevier Science Publishing Co., Amsterdam.

Siriwardena, P.P.G.S.N., 1989. Survey on Aquaculture (Phase 2), Sri Lanka. Unpublished document prepared for the Asian Productivity Organization, Tokyo, Japan.

Siriwardena, P.P.G.S.N., 1990. Aquaculture in Sri Lanka's coastal environment: activities, contributions, conflicts and projections. Unpublished document prepared for the Coastal Resources Management Project, Department of Coast Conservation, Sri Lanka.

Siriwardena, P.P.G.S.N. and P.W.C. Dayaratne, 1990. Report of the technical committee on Dutch Canal rehabilitation for shrimp farming. Unpublished report prepared for the National Aquatic Resources Agency (NARA), Colombo 15, Sri Lanka.

Sunaryanto, A. and A. Mariam, 1986. Occurrence of a pathogenic bacteria causing luminescence in penaeid larvae in Indonesian hatcheries. Bull. Brackishw. Aquacult. Developm. Cent. 8: 64–70.

Weerakoon, D.E.M., and P.P.G.S.N. Siriwardena, 1988. Final report on cage and pen culture roject to the International Development Research Centre, Canada. Inland Fisheries Division, Ministery of Fisheries, Colombo, Sri Lanka, 80 p.

2 Editor's note: As there exists little published data on Sri Lankan shrimp culture, citations for the unpublished documents of Joseph (1993), NARA (1989), Siriwardena (1989, 1990), Sirwardena and Dayaratne (1990) and Weerakoon and Siriwardena (1988) are included as an aid to future workers.

Table 1. Changes in some water quality parameters in the Dutch Canal. 1
Parameter198319871992
pH4.8 – 6.05.3 – 7.37.2 – 8.8
Salinity0.0 – 26.00.0 – 33.00.0 – 33.0
Phosphate (ppm)0.02 – 0.500.05 – 0.850.03 – 2.00
Nitrate (ppm)0.01 – 1.600.01 – 2.700.02 – 3.40
Nitrite (ppm)NA20.02 – 0.320.20 – 1.40
Sulfide (ppm)NA0.02 – 0.610.20 – 1.80
Temperature (°C)23.0 – 32.023.0 – 32.025.0 – 32.0
Turbidity (NTU)5.0 – 19.07.0 – 23.05.0 – 98.0
Total suspended   
solids (mg/L)10 – 2230 – 16050 – 300

1 Source: Jayasinghe (1995).
2 NA = not available.

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