Blackwell Science, LtdOxford, UKFISFisheries Science0919-92682005 Blackwell Science Asia Pty Ltd 2005714791798Original ArticleIncentive for shift in water managementC Kasai et al.

FISHERIES SCIENCE 2005; 71: 791–798

Incentive for shifts in water management systems by shrimp culturists in southern

Chifumi KASAI,1 Thongchai NITIRATSUWAN,2 Osamu BABA3 AND Hisashi KUROKURA1*

1Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan, 2Faculty of Science and Fisheries Technology, Rajamangala Institute of Technology, Trang 92150, Thailand and 3Faculty of Fisheries, Tokyo University of Marine Science and Technology, Tokyo 108-8477, Japan

ABSTRACT: Water management systems and other business situations of shrimp culturists were surveyed in two in southern Thailand. There were three types of water management systems in southern Thailand, namely closed, semiclosed and open systems, categorized by the frequency of exchange of pond water. Shrimp culturists in those districts tended to shift their system from the open system to the closed system of their own accord, and the average net income ratio decreased due to the change of water management system in a from more than 2 to less than 1. The reason for this shift, in spite of the decrease in the profit rate, was prevention of infectious disease caused by water exchange. In conclusion, it was proven that independent shrimp culturists, such as medium and small scale shrimp pond owners in southern Thailand, would accept short-term decreases in profit rate in order to stabilize production.

KEY WORDS: closed system, incentive, shrimp culture, Thailand, water management.

INTRODUCTION propagation of infectious disease and degradation of environment, such as cutting down the stocking Cultured shrimps are the main product for export density and feeding levels, are unpopular with in several developing countries. At the same time, aquaculturists as those countermeasures decrease because of recent worldwide interest in environ- production. mental conservation, shrimp culture has received The authors’ objective is to obtain useful and recognition as a major pollutant source in coastal important information for improvement and prop- environments.1 Therefore, there needs to be a new agation of sustainable shrimp culture methods in enlightened approach from shrimp culturists in developing countries by studying the experience of developing countries to reduce pollutant from the aquaculturists and the present status of shrimp culture ponds. culture in Thailand. The factors which prompted From the 1970s, giant tiger prawn Penaeus mon- the shift in culture methods were considered to be odon culture has developed in south-east Asia, and of particular importance. In this study, the authors the culture areas have now expanded beyond those selected two districts in Thailand as research sites, borders. In countries such as Taiwan, the shrimp and conducted personal interviews with shrimp culture industry decreased their activities after culturists to assess the process of changes in rapid development because of environmental aquaculture methods and the incentives which degradation.2 In contrast to those countries, the affect the selection of culture methods. shrimp culture industry in Thailand is continu- ously expanding to keep up its leading position in the world in terms of production, overcoming the MATERIALS AND METHODS damage of infectious disease, coastal environment pollution, and economic crisis. Generally, effective The present study was mainly composed of three and sustainable countermeasures to reduce the interview surveys. The locations of the survey areas are shown in Fig. 1. The first preliminary survey was performed in Trang Province in 2001 to obtain *Corresponding author: Tel: 81-3-5841-7500. basic information about the typical modern Fax: 81-3-5841-5187. Email: [email protected] shrimp culture industry in southern Thailand. Received 30 September 2004. Accepted 8 February 2005. Trang Province faces the Andaman Sea, the coastal

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ease. Shrimp culture in Trang is more intensive compared to other provinces. Trang Province was known as the place where high productivity (pro- duction from unit area) could be achieved from the initiation of the modern shrimp culture industry.3 Because of a lack of follow-up research in this area, it is not clear whether the high productivity in this area is still maintained or not. For a detailed survey, the authors selected Sikao district as a typical area of shrimp culture in Trang Province. Sikao is located in the western part of Trang Province and the main industry is rubber plantation. The authors randomly selected 18 cul- ture shrimp farms located within 3 km of the coast in Sikao and conducted an interview survey in July and August 2002, asking about the water manage- ment system and their business situation. Simultaneously, 26 shrimp farms in Ranot dis- trict in were surveyed for com- parison. Songkhla is located on the other side of Trang in the Malay Peninsula and faces the Gulf of Thailand. The area of Songkhla province is 7393 km2, and the land is flat with a large brackish lake () in the central part of the prov- Fig. 1 Locations of survey area. ince. The maximum tidal range on the coast is 1.8 m. Generally, the coast of the Gulf of Thailand is stagnant when compared with the coast of the Andaman Sea. However, the coastal water of area which has been recently developed for shrimp Songkhla is not stagnant and water quality is better culture in Thailand.3 The authors performed the than the inner part of the Gulf of Thailand, because survey in the coastal districts of Trang (Kangtan, there is a water current along the coast of Songkhla Sikao, Palian, Yan Ta Khao, Hat Samran) from Sep- Province. Annual rainfall in Songkhla is 1400– tember to November 2001. In these districts, 13 2000 mm with 140–160 rainy days. The modern shrimp farms were surveyed in Kangtan district, 11 shrimp culture industry in Songkhla started during in Sikao district, eight in Palian district, two in Yan the same period as that in Trang, although the Ta Khao district, and one in Hat Samran (a total of development in terms of the increase in number of 35 farms). Shrimp culturists in these areas can eas- shrimp culture farms was more rapid in Songkhla. ily obtain information on modern shrimp culture The number of shrimp culture businesses in techniques from shrimp culturists in Nakhon Si Songkhla reached 1424 in 1991, and the maximum Thammarat, a major culture shrimp production number of 1995 farms was recorded in 1994. Pro- area in Thailand. Trang Province is mountainous, ductivity was also high in Songkhla as in Trang, and shrimp culture was performed using small flat with an extremely high productivity (0.744 kg/m2) areas along the mangrove canal. The coast is recorded in 1989, though the value decreased rap- mainly covered with mangrove forest. The maxi- idly to half of the maximum record in 1991 due to mum tidal range is 3.7 m and the current along the the damage caused by infectious disease. Ponds in coast is strong throughout the year. Stagnation of the Songkhla province were mainly constructed in coastal water scarcely occurs. Annual rainfall is paddy fields or palm plantations. Ranot District is 1700–2400 mm with a total of 140–180 rainy days. flat and located towards the northern border of the The rainy season starts in May and continues to province, bordering on Nakon Si Thammrat, the October. The dry season is from November to April. major culture shrimp production area in Thailand. The major industry in the province is rubber plan- The authors prepared a questionnaire asking tation. The modern shrimp culture began in 1989, mainly about pond water management systems. and the number of shrimp culture farms increased From the results of the preliminary survey, the rapidly from 1991 to 1994. The number reached water management systems were categorized into more than 1000 in 1995, though the number the following three types: open system, pond water decreased to around 700 in 1996 because of a is exchanged from the first month of culture to decrease in production caused by infectious dis- maintain water quality; semiclosed system, water

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was exchanged only from the third month; and Table 1 Outline of shrimp farms in Trang province in closed system, water was not exchanged during the 2001 culture period. Other items in the questionnaire Average of 35 shrimp farms were: place (distance from mangrove canal, dis- Number of ponds 3.9 tance from coast), number and size of the ponds; Average pond size 5148 m2 year and reason for the shift (in cases where the Duration of one crop 108 days water management system was shifted); frequency Stocking density at the beginning of water change per month and total number in dry season 55.7 inds./m2 each water management system; water exchange wet season 60.7 inds./m2 Survival rate 0.48 ratio in each change; side business, source of main 2 income (if the pond owner had a side business); Productivity from unit area 0.43 kg/m Farm gate price 206.7 Bahts/kg production costs; yield (kg and Bahts); use of Average success in production† 0.618 chemicals, probiotics and antibiotics; and sources Total production costs‡ 168.1 Bahts/kg of information. For feed 89.1 Bahts/kg For the evaluation of the impact on profit mar- Seed 20.0 Bahts/kg gins by water management shifts, net income Chemicals 18.4 Bahts/kg ratios (NIR) were calculated before and after a Fuel 32.8 Bahts/kg water saving shift using the following equation: Workers§ 4.6 Bahts/kg Electricity 3.1 Bahts/kg NIR = (total income - total production cost)/total Net income ratio¶ 0.679 production cost (1) †Ratio of farms which could achieve their production goals. For the analysis of the business situation of shrimp ‡Average of 11farms which provided reliable data of culturists in Trang Province, the authors used the production costs. following equations to estimate the total produc- §Including costs for family labor, assuming payment for one labor is 4000 Bhats/month. tion costs, total gross income, and expected value ¶ of net income, per one crop, assuming that farmers (Total income –total production cost)/total production cost. Average of 10 farms which provided reliable data of production can not get any income in the case when they can costs and succeeded in their last production. not achieve their production goal: TPC = TPP ¥ PA ¥ AP ¥ PN (2) TIC = TPC ¥ NIR (3) palm plantations. A total of 15 and nine farms con- structed their pond in paddy fields and in rubber EIC = TIC ¥ PS - TPC ¥ PF (4) plantations (multiple answers were allowed), where, NIR, net income ratio; TPC, total produc- respectively. Most farms (48.5%) constructed tion cost for one crop (Bahts); TPP, total produc- ponds on their own land, and 21.1 and 18.2% tion cost per unit production (Bahts/kg); PA, rented the land from private companies and the production per unit area (kg/m2); AP, average pond government, respectively. Owners who bought size (m2); PN, average number of ponds in a farm; land to construct ponds at the start of the business TIC, total gross income in one crop; EIC, expected were rare (9.1%). Most owners (85.7%) of farms value of net income; PS, probability of success were generally managing other businesses and (average success in production in Table 1); and PF, only 14.3% managed only the shrimp farm. How- probability of failure (1-PS). ever, among the owners who had side businesses, 58.3% got their income mainly from shrimp cul- ture. Other owners obtained their main income RESULTS from rubber plantations (12.5%) and palm planta- tions (8.3%). Among the 35 shrimp farms surveyed in Trang The average number of ponds in a farm was Province, 14 farms started shrimp cultures 3.9 ± 3.4 (standard deviation) and the average total between 1991 and 1994, when the highest produc- area of a farm was 2.07 ± 2.08 ha. Pond water was tivities were recorded in Trang. A total of 16 out of introduced from mangrove canals in 94.1% of the 26 farms which answered this question (61.5%) farms and the other farms got seawater directly started shrimp cultures in order to get higher from the coast. Several farms (17.9%) had precipi- income compared to other business, and five farms tation ponds and water was stored in these ponds (19.2%) began shrimp cultures as a hobby. In total, for several days before being used, while in the 12 owners had been involved in rubber plantations other farms, water was supplied directly to the cul- before the initiation of shrimp cultures, 8.9% were ture ponds. The average maximum salinity in each official employees, and 8.9% were managers of farm was 24.8 while the lowest was 7.1.

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1990 1995 2000 year Farm No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Fig. 2 History of water manage- 16 ment shifts in Sikao district, Trang 17 Province, Thailand. Each bar 18 indicates a shrimp farm. Abscissa Open system axis indicates year, and patterns Semi-closed system of the bars represent the type of Closed system water management system.

After the harvest of the previous crop, bottom 0.43 kg/m2 (ranging 0.21–1.09 kg/m2) during the mud containing feces and uneaten diet was research period. Generally, productivity was high removed from the pond by bulldozer. The bottom in the rainy season. When production costs were was then flattened and dried. Several days before calculated as the sum of feed, seed, drugs, fuel introduction of water, the bottom was sanitized and electricity, the average production cost was and neutralized by lime. The water condition was 163.5 Bahts/m2. In cases when mass mortality adjusted by adding fertilizer and other chemicals occurred, shrimp culturists could scarcely get any for 1 or 2 weeks before stocking of post larvae 12– income. Among the 35 farms, 61.8% achieved their 13. The average stocking density was significantly production goal in the last crop of the survey (P < 0.05, paired t-test) low in the dry season period, and the net income ratio in these farms was (55.7 ± 14.2 inds/m2) and high in the wet season 0.679 (Table 1). Shrimp culturists made efforts to (60.7 ± 10.9 inds/m2) because one-third of the modify their protocols to improve production. farms decrease the density in the dry season. Pond Information about such modifications was managers explain the reason for the decrease being obtained from other shrimp culturists for 42.4% of that they could not depress the frequency of water farms, 15.2% farms obtained it from diet and drug exchange in high stocking density though the traders, and 18.2% farms adjusted their protocols chance of water exchange was limited in the dry using only their own experiences. No differences in season because of contamination of pathogen in management, methods or the economic back- coastal water. Feeding protocols such as the ground of shrimp culture among these five districts amount and number of times a day differed among were found. farms and were changed in relation to the growth Figures 2 and 3 show the histories of shifts in rate and condition of the shrimp. Every farm used water management systems of each farm in Sikao drugs (vitamins, probiotics, antibiotics* and other and Ranot district. Of the 18 shrimp farms which chemicals) for the maintenance of water condi- answered the questionnaire in Sikao, two farms tions and shrimp health. The combination of drugs changed from an open system to a closed system, and protocol differed among farms. The average and four farms shifted from an open system to a culture period was 108 days (ranging 80–140 days) semi-closed system. Four farms each started as and the average harvest size was 15.5 g/inds. Farm open system and semi-closed system farms, and gate prices of shrimp differed between size classes they still used the same system at the beginning of and were determined in the Mahachai Market 2002. Two farms that started in 2000 are closed (near Bangkok). The average farm gate price system farms, and only two farms shifted from was 206.4 Bahts/kg, and average productivity was a closed system to an open system. On the whole, the ratio of open system, semi-closed system and *Use of all antibiotics was banned in Thailand from 2002. closed system changed from 64, 27 and 9%, at the

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1990 1995 2000 year Farm No. 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 Fig. 3 History of water manage- 40 ment shifts in Ranot district, 41 Songkhla Province, Thailand. 42 Each bar indicates a shrimp farm. 43 Abscissa axis indicates year, and 44 patterns of the bars represent Open system the type of water management Semi-closed system system. Closed system beginning of 1995, to 33, 44 and 22% at the begin- ning of 2002, respectively. Out of the 26 farms in 300 Sikao Ranot district, 11 farmers shifted from an open sys- tem to a closed system, two farms shifted from an 200 open system to a semi-closed system, and only one farm shifted from a closed system to an open sys- 100 tem. Of the other 12 farms not shifted, 4, 3 and 5 employed an open system, semi-closed system and closed system, respectively. The ratios of open, 0 semi-closed and closed systems changed from 69, 23 and 8% at the beginning of 1995, to 19, 19 and 62% at the beginning of 2002, respectively. If the 300 shift from open to semi-closed, open to closed, and Ranot semi-closed to closed are defined as water saving 200 shifts, then 33 and 50% of shrimp farms in Sikao and Ranot districts, respectively, have selected water saving shifts during the period from 1995 to 100 2002. Production cost (Bahts/kg) Figure 4 shows a comparison of unit production 0 costs for the last crop among the three systems in Open Semi-closed Closed each district. There were large differences in pro- Water management system duction costs in Sikao district (P < 0.001 ANOVA). The costs in the closed systems were more than feed seed fuel electricity workers others threefold the costs in the open systems, with costs in the semi-closed systems only slightly higher Fig. 4 Unit production costs in Sikao and Ranot than the open systems. A similar trend was districts, Trang and Songkhla Provinces, Thailand, observed in Ranot district, though the differences respectively.

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0.8 4 Sikao Sikao 0.6 3 )

2 2 0.4

1 0.2 0 0

4 0.8 Ranot Ranot 3 0.6

Net Income ratio 2

0.4 1 Productivity (kg/m 0.2 0

0 Open Semi-closed Closed Fig. 6 Changes in net income ratio in Sikao and Ranot Water management system districts, Trang and Songkhla Provinces, Thailand, respectively, by the water saving shift. Vertical bars indi- Fig. 5 Production per unit area in each water manage- cate standard deviations. ment system in Sikao and Ranot districts, Trang and Songkhla Provinces, Thailand, respectively. Vertical bars indicate standard deviations. in the closed systems in both districts. It is obvious that productivity decreased and production costs increased as a result of water saving shifts from were not so prominent as in Sikao district. In the open systems to semi-closed systems or from closed systems in Sikao district, the costs for feed, semi-closed systems to closed systems. Generally, seed and oil accounted for nearly 90% of the total water volume is an important factor which deter- production costs. Figure 5 shows the productivity mines the capacity of cultured aquatic animals in a of the last crop per unit area in each water system pond which has no special water treatment system, in each district. Productivity was the highest in the such as water circulation system with bio-filter. open systems and the lowest in the closed systems Hopkins et al.4 performed a comparison between in both districts and overall was higher in Ranot open and closed system experimental shrimp district than in Sikao district. In Sikao district, pro- (P. vannamei) ponds at a density of 38.2 shrimps/ ductivity in the closed systems was less than half of m2, and concluded that there was no significant that in the open systems. As shown in Fig. 6, the net difference in the growth and survival of shrimps income ratio decreased significantly (P < 0.05, between the two systems, but 31.5% of electricity paired t-test) for all farms which selected water costs could be saved using a closed system. How- saving shifts in Sikao district with the average net ever, in a similar experiment for the detection of a income ratios decreasing from more than 2 to less combination effect of system type with stocking than 1. A similar trend was observed in Ranot dis- density, there was mass mortality in closed systems trict, though the decrease in net income ratios was with high stocking densities (66 inds/m2).5 They smaller (statistically not significant). concluded that reduced water exchange was cru- cial for the high density production of shrimps. Average stocking density in Trang was 58.2 inds/ DISCUSSION m2. In such conditions, farmers should decrease stocking density and production goals in conjunc- Although production costs differed between Sikao tion with the water saving shift. Several costs, such district and Ranot district, they were the highest in as feed and seed, depend on the number of cul- the closed systems and the lowest in the open sys- tured animals, while other costs such as chemicals, tems in both districts. Similarly, productivity was fuel and electricity for maintenance of water con- the highest in the open systems and was the lowest ditions depend on pond size. A decrease in net

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income ratios will automatically occur as unit pro- when frequency of infectious disease was higher duction costs increase due to the water saving than the wet season, in order to decrease the fre- shift. However, it is possible to minimize the fall in quency of water exchange. This means that farmers income ratios by improving the survival rate and had knowledge about the relationship between food conversion efficiency. In Sikao district, the water exchanging frequency and risk of infectious costs of feed and seed were prominently higher in disease. The coast of Ranot district is more polluted closed systems than in the other systems, and than that of Sikao3 and farmers in Ranot have less these costs pushed up the total production costs. chance to get safe water. This is one reason why In contrast, the differences in the cost of feed and they shifted water management systems earlier seed between a closed system and other systems than in Sikao. Ranot district has also suffered seri- were not so large in Ranot district. As a result, the ous propagation of infectious disease more often decrease in net income ratio by water saving shifts than Sikao district,3 as it is located within the Gulf was smaller in Ranot district. Many farmers in of Thailand, and this is probably another reason for Ranot district shifted their water management sys- making the shifts. tem earlier than in Sikao district and they had more The total production cost per one crop calcu- experience of closed systems than the farmers in lated from data in Table 1 using equation 2 was Sikao district. Presumably, farmers in Ranot district 1 451 000 Bahts. The average net income ratio was can culture shrimps in closed systems at survival 0.679 and income from one crop was estimated to rates and food conversion efficiencies similar to be 985 000 Bahts. The expected income from one other systems using their empiric knowledge. This crop, taking into consideration the probability of indicates that shrimp farmers can overcome the successful production and assuming that farmers technical difficulties of closed system shrimp can not get any income in the case of failure, was culturing and earn a good income. estimated to be 54 000 Bahts by using equation 4. Another interesting question to be discussed The average production period for one crop is here is the motive behind the selection of water nearly 4 months, but the farmers need to dry the saving shifts. Closed system shrimp culturing was pond for a while to maintain pond conditions. developed in central Thailand in the late 1990s.6 In Therefore, if it is assumed that the actual produc- those days, shrimp culture ponds were constructed tion period, including pond preparation, is using paddy fields in inland freshwater areas and 5 months, then the expected monthly net income concentrated seawater was transported from salt per farm is 10 800 Bahts. fields on the coast to the ponds and used for pond Table 2 shows the monthly income of industrial water. The cost of water was a large proportion of workers in Thailand in 2000.7 Expected monthly production costs in inland closed system shrimp net income from shrimp farms is higher than these cultures and water saving was essential in these values. However, it cannot be said that the income systems. After shrimp culture in freshwater areas in of shrimp farmers is higher than workers in other Thailand was banned by law because of salt pollu- industries, because costs for pond construction, tion of paddy fields, shrimp farmers in several pond rental fee, and preparation cost for ponds coastal areas adopted the closed system. Farmers were not included. Therefore, the calculated value selected their culture system depending mainly on is an overestimation. As shown in the results of their personal experiences. There are many possi- business conditions of shrimp farmers in Trang, ble reasons for the selection of water management shrimp farmers in Southern Thailand are mainly systems. Water saving itself can not be any incen- small investors, such as merchants, owners of tive for the adoption of water saving shifts for the farmers in coastal areas, because they can get enough water from the coast or canals at low cost. The most likely incentive for the water saving shift Table 2 Monthly wages of industries in Thailand in the year 2000 (in Bahts) is the avoidance of infectious disease. The exchange of pond water with coastal water is a Average of industries 6 628 major opportunity to introduce pathogens to Agriculture 3 147 culture ponds in areas where culture ponds are Mining industry 6 332 densely distributed. In the report of a survey per- Manufacturing industry 5 846 formed in 1995, it was suggested that shrimp farm- Construction industry 4 872 Electric and water service 13 675 ers are reducing the frequency of water exchange Commerce 8 265 due to the risk of importing disease into farms with 3 Transport 11 465 water supply from the surrounding environment. Others 10 095 In fact, a considerable number of farmers reduced stocking density of the shrimp in the dry season, From data from the National Statistic Office of Thailand.7

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plantation, and civil officers. The total cost per one Research Council of Thailand for granting permis- crop is a large investment for them and the equa- sion to conduct this research in Thailand. This tion for the estimation of EIC indicating that the study was supported in part by a Grant-in-Aid for possibility of success (PS) is a critical parameter International Scientific Research from the Ministry which determines the income. Only a several per- of Education, Science, Sports and Culture of Japan centage decrease of PS will make the balance pas- (No. 10041160) and from Japan Society for the Pro- sive. The authors assumed in this calculation that a motion of Science. (No. 15255017). For the analysis farmer could not get any income in the case that of the data, the authors were financially supported they could not achieve their production goal. It is by the research project ‘Water management system thought that this assumption is substantially real- of the Mekong River’ under Core Research for Evo- istic, because the infectious disease which inflicted lutional Science and Technology by Japan Science serious damage to the shrimp farmers in Trang and Technology Agency. Province and Songkhla province is thought to be white spot disease from their symptom,8 pattern of propagation9 and the period of the epidemic,10 and REFERENCES invasion of white spot disease virus in shrimp cul- ture pond brings catastrophic damage to produc- 1. Boyd CE. Guidelines for aquaculture effluent management tion. White spot disease is caused by infection of at the farm-level. Aquaculture 2003; 226: 101–112. White Spot Syndrome Virus and inflicts cata- 2. Thonngrak S. Sustainable shrimp farming in Thailand. PhD strophic damage on cultured shrimp. This disease, Thesis. University of Missouri, Columbia, 1995. combined with Yellow Head Virus disease, has 3. Network of Aquaculture Centres in Asian-Pacific (NACA). A Survey of Water Pollution Sources from Coastal Aquaculture. caused the loss of 70 000 mt (around 40% of total 11 NACA, Bangkok. 1995. production/year) in 1996 in Thailand. 4. Hopkins JS, Sandifer PA, Browdy CL, Holloway JD. Compar- The survey also indicates that the farmers inten- ison of exchange and no-exchange water management tionally accepted the decrease of net income ratio. strategies for the intensive pond culture of marine shrimp. J. They understood that they should accept a short- Shellfish. Res. 1996; 15: 441–445. term decrease in benefit to enable stable and sus- 5. Hopkins JS, Hamilton RD, Sandifer PA, Browdy CL, Stokes tainable production of shrimps. Therefore, at least AD. Effect of water exchange rate on production, water in Southern Thailand, where most of the pond quality, effluent characteristics and nitrogen budgets of owners are local small investors, shrimp farmers intensive shrimp ponds. J. World Aquacult. Soc. 1993; 24: accept decreases of short-term benefits once they 304–320. 6. Boyd CE. Inland shrimp farming and the environment. understand that sustainability of production can World Aquacullt. 2001; 32: 10–12. be maintained by accepting the decrease. 7. National Statistic Office. The 2000 Population and Housing Census. National Statistic Office, Bangkok. 2001. 8. Momoyama K, Hiraoka M, Nakano H, Koube H, Inoue K, Oseki N. Mass mortality of cultured Kuruma shrimp, ACKNOWLEDGMENTS Penaeus japonica, in Japan in 1993: histopathological study. Fish Pathol. 1994; 29: 141–148 (in Japanese with English Many undergraduate and graduate students in the abstract). Faculty of Science and Fisheries, Rajmangala Insti- 9. Nakano H, Koube H, Umezawas S, Momoyama K, Hiraoka tute of Technology, joined the research survey as M, Inoue K, Oseki N. Mass mortality of cultured Kuruma translators. The authors would not have obtained shrimp, Penaeus japonica, in Japan in 1993: epizootiological any data without their support. The authors surveyand infedtious trials. Fish Pathol. 1994; 29: 135–139 express here their sincere thanks to them and to (in Japanese with English abstract). the shrimp farmers who participated in the inter- 10. Flegel TW. Special topic review: major viral disease of the black tiger prawn (Penaeus monodon) in Thailand. World J. view survey. The authors are grateful to Dr Puth Microbiol. Biotech. 1997; 13: 433–442. Songsangjinda, Marine Shrimp Culture Research 11. Chanrachakool P, Phillips MJ. Social and economic impacts and Development Institute, Department of Fisher- and management of Shrimpdisease among small-scale ies, for his informative suggestions and support in farmers in Thailand and Viet Nam. FAO Fish. Tech. Paper the research in Ranot district, and to the National 2002; 406: 253–286.