Coastal Shrimp Aquaculture in Thailand: Key Issues for Research

!process of conversion. Some farms are now the sites of large-scale residential developments,while others have been excavated to provide soil for these projects.The national level of shrimp production has been maintained by the increase inthe number of farms and increased production along the eastern and southern coasts.However, farms in these areas have also experienced problems of environmental degradation(DOF 1994) resulting in production decreases (Funge-Smith, cited in Briggsand Funge-Smith 1994). Since the mid-1990s, the regular occurrence of white spotdisease has seriously impacted on farm productivity and has caused the closure offarms in some areas (Flegel 1996; Funge-Smith 1997).The pattern of expansion and intensification of shrimp farming followed bydisease problems has been seen elsewhere in the world. In Taiwan in 1988, annualproduction dropped by over 75% from the previous year (Lin 1989), and betweenSeptember and mid-December 1994, US$64 million worth of shrimp were lost in twoprovinces in Vietnam. Government officials there attributed the losses to disease outbreaksresulting from unplanned and spontaneous shrimp culture (Anon. 1994b).China has also experienced serious shrimp crop losses.Diseases in the Thai industryThe mortality of shrimp in Taiwan in 1988 was attributed to bacterial and viraldiseases which were exacerbated by a number of non-pathogenic factors. Thesewere:• degradation of culture ponds;• an increase of stocking densities to unreasonably high levels;• defects in formulated feeds;• indiscriminate use of antibiotics and medicines;• inadvertent or unavoidable use of polluted water;• lack of technical training of shrimp farmers; and• absence of a reliable system of sanitation (Chien 1992).Shrimp disease outbreaks have occurred in Thailand in the 1990s (Flegel 1996;Funge-Smith 1997; Anon. 1998b). In a Network of Aquaculture Centres inAsia–Pacific (NACA 1994a) survey, 75% of farmers stated that they had had problemswith shrimp diseases. Of these, 25% reported yellow head, 22% one-monthdeath syndrome, and 21% black gill disease. Other reported diseases were swollengill, black splinter, red body, tail rot and crooked leg diseases. Of the surveyed farmers,46% had problems with disease twice per crop, 36% once per crop, and 17%once a year. There was a higher incidence of particular diseases depending on proximityto either the sea or a canal. This was considered suggestive of a relationshipbetween these diseases and water quality (NACA 1994a). Yellow head and red bodydisease were most commonly encountered at farms using canal water. Black gill andone-month death syndrome were most common near the sea. Since 1994, white spotvirus has been a major cause of disease in Thailand, as in other countries in the region(Flegel 1996).Disease-causing organisms are probably widespread and abundant in shrimpunder culture conditions even in the absence of disease. Studies in Indonesia found+"