FISHERIES SCIENCE 2005; 71: 791–798 Blackwell Science, LtdOxford, UKFISFisheries Science0919-92682005 Blackwell Science Asia Pty Ltd 2005714791798Original ArticleIncentive for shift in water managementC Kasai et al. *Corresponding author: Tel: 81-3-5841-7500. Fax: 81-3-5841-5187. Email: akrkrh@mail.ecc.u-tokyo.ac.jp Received 30 September 2004. Accepted 8 February 2005. Incentive for shifts in water management systems by shrimp culturists in southern Thailand Chifumi KASAI, 1 Thongchai NITIRATSUWAN, 2 Osamu BABA 3 AND Hisashi KUROKURA 1 * 1 Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan, 2 Faculty of Science and Fisheries Technology, Rajamangala Institute of Technology, Trang 92150, Thailand and 3 Faculty 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 districts 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 district 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 Cultured shrimps are the main product for export in several developing countries. At the same time, because of recent worldwide interest in environ- mental conservation, shrimp culture has received recognition as a major pollutant source in coastal environments. 1 Therefore, there needs to be a new enlightened approach from shrimp culturists in developing countries to reduce pollutant from culture ponds. From the 1970s, giant tiger prawn Penaeus mon- odon culture has developed in south-east Asia, and the culture areas have now expanded beyond those borders. In countries such as Taiwan, the shrimp culture industry decreased their activities after rapid development because of environmental degradation. 2 In contrast to those countries, the shrimp culture industry in Thailand is continu- ously expanding to keep up its leading position in the world in terms of production, overcoming the damage of infectious disease, coastal environment pollution, and economic crisis. Generally, effective and sustainable countermeasures to reduce the propagation of infectious disease and degradation of environment, such as cutting down the stocking density and feeding levels, are unpopular with aquaculturists as those countermeasures decrease production. The authors’ objective is to obtain useful and important information for improvement and prop- agation of sustainable shrimp culture methods in developing countries by studying the experience of the aquaculturists and the present status of shrimp culture in Thailand. The factors which prompted the shift in culture methods were considered to be of particular importance. In this study, the authors selected two districts in Thailand as research sites, and conducted personal interviews with shrimp culturists to assess the process of changes in aquaculture methods and the incentives which affect the selection of culture methods. MATERIALS AND METHODS The present study was mainly composed of three 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 basic information about the typical modern shrimp culture industry in southern Thailand. Trang Province faces the Andaman Sea, the coastal