Coastal Shrimp Aquaculture in Thailand: Key Issues for Research

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!Production Practices and TechniquesThe production methods and management practices of shrimp farms vary betweenareas and between individual farms. Furthermore, the methods employed by eachfarmer are necessarily dynamic, governed by the changing condition of the shrimp,the water quality of the ponds, and by the acquisition of new knowledge. This lack ofconsistency makes it difficult to describe the exact practices involved in shrimp farming.Instead, an overview of techniques and principles is presented here. As intensivefarming produces most of Thailand’s shrimp, this method of production is given themost attention.Larvae and hatcheriesThe development of hatchery techniques in the late 1960s (Liao 1990), togetherwith successful induction of spawning in tiger and banana shrimp in 1973 (Suraswadi1990) allowed shrimp farmers to increase stocking densities and consequently production.Prior to this, only wild seed stocks were available which were not alwaysreliable. At present, very few farms use wild-caught postlarvae in Thailand (M.J.Phillips, pers. comm.).In Thailand in 1989, there were 2,000 private hatcheries producing an estimated12,100 million shrimp juveniles (Suraswadi 1990). In 1997, there were an estimated1,000 hatcheries (Funge-Smith 1997). Government fishery research stations are alsoinvolved in the production and supply of postlarvae. Concrete tanks or shallow pondsmade of bricks are generally used, allowing minimal costs for construction and operation.Other operations use fibreglass tanks. Hypersaline water is often obtained fromsalt pans—this is relatively free of pathogens because of its high salinity. The survivalrate in hatcheries may be as high as 95% (Suraswadi 1990), however it isusually between 40–50% in small-scale hatcheries.Juveniles are purchased by farmers at between 10 and 30 days after moulting tothe postlarvae stage (PL10–30), but usually between 14 and 18 days (PL14–18)(NACA 1994a). In 1997, prices for PL12–15 were US$3.43 to US$4.06 per thousand(Funge-Smith 1997).Stocking densityStocking density is determined by a number of factors including pond size,quality of the available water supply, the type of technology used by the farm and thelevel of production desired. The goal of the farmer is, understandably, to achieve thegreatest possible production to maximise profits. In many instances, farmers stocktheir ponds at a very high density initially with the intent to offset losses incurredlater. A particular stocking density, however, does not ensure a particular output(NACA 1994a) as mortality rates vary. Reasons for this include death of larvae fromthe stresses induced by transport or disease or—at later stages in growth—fromdisease or from syndromes related to deterioration of water quality. A study by Chaiyukumet al. (1992, cited in NACA 1994a) found a very variable survival ratebetween the time of initial stocking of ponds and harvest (25.9–81.5%), even with arelatively low stocking density of 25 shrimp/m 2 .+%
!Pond carrying capacityThe carrying capacity of a pond is generally defined as the maximum density ofshrimp which can be supported by the pond environment whilst maintaining optimalshrimp health and growth rates. The pond’s carrying capacity is naturally a functionof the capacity of the environment surrounding the pond to assimilate its wastes andto cope with its other environmental impacts (see below—section on impacts ofshrimp farms). Stocking densities in excess of the pond’s carrying capacity lead tolower production levels, and in the event of severe deterioration in environmentalquality, crop loss from disease. The carrying capacity varies depending on numerousfactors, including features of the pond site, water quality and exchange, and pondmanagement practices.Analysis of data from detailed crop histories by Corpron (cited in Fegan 1994)established that beyond a density of 6 t/ha/crop there was a marked reduction infeeding and growth rate. Based on these data, rather than specifying a desirablestocking density, the Aquastar Company directed its farmers to limit production to 6t/ha/crop as a measure toward the goal of achieving sustainable production (Fegan1994). If the pond is densely stocked, the company recommends that at least partialharvest be performed when this level is reached; the remainder of the shrimp can beharvested later when at a larger size. Hirasawa (1992) also identified 6 t/ha/crop as anupper limit for production in a study of feed conversion ratios (FCRs). Above thisstocking density, FCRs began to increase sharply. He attributed this to a criticalchange in the ecology of the pond which occurs at higher stocking densities,adversely affecting natural pond productivity (i.e. the growth of plankton on whichshrimp feed). Despite these findings, some farmers harvest 9–12 t/ha/crop (DOF1994). There is clearly a need to carry out research in order to better understand theinteractions of pond dynamics, pond microbiology and productivity.Water supply and qualityIn general, water used for shrimp rearing should be within the temperature andsalinity ranges suitable for the species under culture and be free of industrial andagricultural pollutants (Apud et al. 1989). The source of the water supply variesdepending on the farm location and the distances over which water must be pumped.Extensive farms rely on tidal inflow, while semi-intensive and intensive farms pumpwater from canals (called khlongs in Thailand), estuaries or the sea. Effluent watermay be discharged into the same water body from which water is taken. Where thereis limited drainage or tidal flushing of that water body, water quality is likely to bepoor. Such conditions may account for a disparity in income found between shrimpfarms using water from different sources in a survey undertaken in the Ranot District(NACA 1994a). There, farms obtaining water directly from the sea earned an averageincome of 81,277 baht/rai/crop while those using canal water earned only 30,263baht/rai/crop.Early shrimp farming operations required the use of brackish water. It wasbelieved that a salinity of 12–25 parts per thousand (ppt) was necessary for shrimpsurvival. Scarcity of water within this range led to the use of water with salinitiesboth lower and higher, and tiger shrimp are now grown successfully in salinities from4–36 ppt (Anon. 1994c). In other areas, a lack of saline water has prompted farms to+&
Page 8 and 9: !The 1994 Workshop had a working hy
Page 11 and 12: !The Workshop at Hat Yai, SongkhlaA
Page 13 and 14: !ReferenceSmith, P.T., ed.. 1999. T
Page 15 and 16: !Shrimp Farming in ThailandOver the
Page 18 and 19: ! !Table 1. World production (# 1,0
Page 20 and 21: !Domestic and world demandJapan is
Page 22 and 23: !Intensification of farms has been
Page 24 and 25: !no significant difference between
Page 28 and 29: !use water which is almost fresh (F
Page 30 and 31: !mended quantities for application
Page 32 and 33: !the biological processes in sedime
Page 34 and 35: !factors (Fegan 1994). Environmenta
Page 36 and 37: !Acid sulphate soils occur in most
Page 38 and 39: during the rainy season, some deter
Page 40 and 41: Land subsidenceCoastal land subside
Page 42 and 43: first when an area becomes environm
Page 44 and 45: !Administration. Their work has inv
Page 46 and 47: agriculture, selects coastal land p
Page 48 and 49: Sustainability, Sustainable Develop
Page 50 and 51: cultural and environmental asset va
Page 52 and 53: $+Table 12. (cont’d) Impediments
Page 54 and 55: $#Table 12. (cont’d) Impediments
Page 56 and 57: $%Table 12. (cont’d) Impediments
Page 58 and 59: capacities of alternative organisms
Page 60 and 61: sources. This is one of the greates
Page 62 and 63: Table 13. (cont’d) Summary of the
Page 64 and 65: Boonyapiwat, S. 1989. Species of ph
Page 66 and 67: Katesombun, B. 1992. Aquaculture pr
Page 68 and 69: Sirisup, S. 1988 Socio-economic cha
Page 70 and 71: !In the preliminary analysis, the s
Page 72 and 73: !until all variables had been teste
Page 74 and 75: !quality problem over the past 3 ye
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!Figure 1. Characterisation of prov
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!Variables Contributing to Shrimp P
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!Figure 5. Relationship between ave
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!southern). The linear regression m
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!Appendix. Results of logistic regr
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!2) Trat ProvinceClassification tab
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!Chi-square df significanceModel Ch
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!8) Satun ProvinceClassification ta
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!Variables in the equationConstant
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!A total of 49 participants were in
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! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !Fi
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!All issues are listed in Appendice
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!!were short term and one issue was
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!reared broodstock (issue 71). They
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!!Two participants commented that i
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mation transfer and training. This
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108Appendix 1. (cont’d) Descripti
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112Appendix 2. Descriptive statisti
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Appendix 5. (cont’d) Descriptive
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Appendix 7. Descriptive statistics
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Appendix 7. (cont’d) Descriptive
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!ParticipantsAustraliaDr Paul T. Sm
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