1 Aquatic Animal Health Research Institute
Department of Fisheries
Kasetsart University Campus
Jatujak, Bangkok 10900, Thailand
2 National Institute of Coastal Aquaculture
Department of Fisheries
Kaoseng, Songhkla, Thailand
Kanchanakhan, S., P. Chanratchakool and S. Direkbusarakom. 2002. The impact of disease on small-scale coastal cage-fish culture in Thailand. p. 203-206. In: J.R. Arthur, M.J. Phillips, R.P. Subasinghe, M.B. Reantaso and I.H. MacRae. (eds.) Primary Aquatic Animal Health Care in Rural, Small-scale, Aquaculture Development. FAO Fish. Tech. Pap. No. 406.
The socio-economic impact of disease in small-scale coastal finfish aquaculture in the east and south of Thailand was assessed during July-September 1999 using a questionnaire. A total of 136 fish farmers were interviewed. The species cultured in the survey area are barramundi (Lates calcarifer) and grouper (Epinephelus spp.). The farms surveyed included 102 seabass farms and 34 grouper farms. The farms are located in four provinces: Satun, Pattani, Chanthaburi and Songkhla. Of the farms surveyed, 119 were cage-culture farms, while only four farms were pond-culture systems; five farms were solely hatcheries, while six farms combined hatchery and pond-culture systems. Two of the seabass farms carried out all of the above culture systems. There were more seabass farms than grouper farms, as seabass seed is more readily available from traders and private hatcheries. Grouper seed supply from hatcheries has been inconsistent due to disease losses. The survey indicates that the majority of the problems in grow-out grouper cage culture and seabass cage culture are due to seasonal variations and disease.
Coastal aquaculture is receiving more attention in fisheries development in Thailand because of the decline in marine capture fisheries. Coastal finfish production has been gradually increasing, and production in 1996 was 4,800 mt (Fisheries Statistics of Thailand 1996). Coastal aquaculture is mostly concentrated in the south and the east coasts. The two fishes most commonly cultured are barramundi, Lates calcarifer (usually referred to as seabass in Thailand), and grouper, Epinephelus spp. The cage-culture system for these two species is similar; however, the market price for grouper (US$10-20/kg) is about five to seven times more than that for seabass (US$2-3/kg). Because of the higher market price, fish farmers tend to culture grouper rather than seabass. Unfortunately, neither the government nor private hatcheries has consistently produced large amounts of grouper seed, and most is presently collected from the wild. However, seabass seed can be produced by hatcheries and is available almost all year. Therefore, small operators, who cannot afford grouper seed, are still farming seabass. Apart from seed supply and problems of market price, disease may be a concern among farmers. In this paper, the impact of disease on small-scale operations is investigated.
A coastal aquaculture survey was conducted in four provinces, Chantaburi, Pattani, Satun and Songkhla. A total of 136 questionnaires were completed for this study, of which 107 were obtained from Songkhla Province. Coastal aquaculture in Thailand is mainly cage-culture systems located in brackish water.
Seabass is the dominant species cultured (75%), while grouper accounts for the remainder (25%). Over 88% of farms practice cage culture, with 9% practising pond culture. Of the cage-culture farms, 50% were small, ranging in cage surface area from 5 to 100 m2. About 62% of the cage fish farmers owned 1-5 cages. Four seabass hatcheries were covered by this survey. Seventy percent of the fish farms bought fry from traders, and 15% of the farms collected seed from the wild.
Of the farmers interviewed, 118 said that production had generally been as good as expected. Average survival rates for cage fish culture were ~60-70%. Farmers seemed to find mortalities of 30-40% per crop acceptable. The total revenue as expressed by the farmers varied from US$25 to $2000/yr. The cost of fish production, ranked from high cost to low cost, came mainly from feed, cage preparation and chemicals. Aquaculture was found to be an important occupation, as over 75% of the farmers spent more than 50% of their time in aquaculture. The main reason given for culturing fish was for income; a secondary reason was for household consumption.
The husband spends more time working in the fish farm, feeding or harvesting the fish, than the wife and children. However, the wife plays an important role in marketing the fish and buying the fry.
Farmers coming into aquaculture normally learn how to grow fish themselves (28%) or obtain the knowledge from their friends (27%); other farmers learn from government officers (21%) or neighbouring farmers (22%).
Cage-culture information was mainly obtained from Songkhla Province, where cage culture is located in the river and the lake, which both open to the sea. The first-ranked problem was low water level in the culture area during the hot season. The second-ranked problem was flooding during the wet season, while disease problems were ranked third.
Coastal finfish cage culture was considered a risky venture by 130 of the 132 farmers interviewed. Surprisingly, 123 of the 132 farmers still considered cage culture to be profitable. However, 81 of 132 farmers said that the profits were not large. 120 of 132 farmers did not believe that large-scale fish farming would bring them large profits. Most of the farmers (128 of 132 farmers) said that disease was an important issue.
Most of the farmers interviewed had good contacts with the Aquatic Animal Disease Unit in the National Institute of Coastal Aquaculture (NICA). Around 55% of the farmers could identify diseases. Results indicate that bacteria, parasites, viruses, and red spots on the body of the fish were the main problems (from high frequency to low frequency) in seabass and grouper culture. However, about 45% of the fish farmers could not identify diseases.
Disease usually occurred within 10-30 days after stocking the fish in the cage. Eighty of 124 farmers indicated that disease problems mainly occurred during the rainy season, while 35 of 124 farmers said that the problem occurred during the hot season. When disease occurred, 99 of 119 farmers reported losses of between 30-50%. The value of lost production varied as shown in Table 1. Over 50% of fish farmers preferred to use drugs or antibiotics to treat their fish. The cost of treatment varied between US$5 - over $500/yr; however, 87% of fish farmers spent around US$5-100/yr. Fifty-nine of 121 fish farmers said that treatments were "usually" effective, while 61 of 121 said that treatments were "sometimes" effective.
Table 1. Value of fish products lost due to disease.
Most of the finfish cage culture in Thailand is comprised of small farms, with farmers usually owning 1-5 cages. Even though farmers felt that cage culture did not make a lot of profit, they would still continue with aquaculture. In small farms, the farmers spent some of their time culturing fish and some on agricultural or fishing activities. Cage culture is located in the shallow water near their homes and is easily polluted by drainage water from the villages or towns. This pollution can have a greater effect on fish health during the hot and wet seasons. Apart from these seasonal variations, disease is also a cause of mortalities. The findings suggest that extension and research programmes are required to improve finfish cage culture in Thailand. It is likely that the 30-40% mortality per crop encountered in finfish cage culture could be reduced following research into the disease problems.
Two different viruses, an iridovirus (Danayadol et al. 1994; Kasornchandra and Khongpradit 1997) and a nodavirus (Danayadol et al. 1995) have been identified as pathogens and capable of causing high mortality. These viruses have been identified in seabass and grouper culture from a wide geographical area, including Southeast Asia, Japan and the Mediterranean. Co-operation among affected countries would assist in controlling these diseases and preventing their spread.
The authors would like to thank the Department for International Development of the United Kingdom (DFID) and the Department of Fisheries of the Royal Thai Government for financial support to carry out this survey.
Danayadol, Y., S. Direkbusakum and K. Supamattaya. 1995. Viral nervous necrosis in brownspotted grouper, Epinephelus malabaricus, cultured in Thailand. p. 227-233. In: M. Shariff, J.R. Arthur and R.P. Subasinghe. (eds.) Diseases in Asian Aquaculture II. Fish Health Section, Asian Fisheries Society, Manila.
Danayadol, Y., S. Direkbusarakum and S. Boonyaratpalin. 1994. Iridovirus-like infection in grouper, Epinephelus malabaricus, cultured in Thailand. Tech. Pap. No. 13-1994, National Institute of Coastal Aquaculture, Songkhla, 12 p. (In Thai, English Abstract).
Kasornchandra, J., and R. Kongpradit. 1997. Isolation and preliminary characterization
of a pathogenic iridovirus in nursing grouper, Epinephelus malabaricus. p. 61-66.
In: T.W. Flegel and I.H. MacRae. (eds.) Diseases in Asian Aquaculture III. Fish
Health Section, Asian Fisheries Society, Manila.