Shellfish (mollusc) of various kinds has always been a very good source of food both for man and other animals useful to man. This is true in the coastal provinces of Thailand. From the fragmentary statistics available, since 1957, the production of the country's shellfish resources has continued to increase and fluctuated through the years (Table 1, Fig. 2). At the beginning, most of the production can be attributable to natural or wild sources but as the grounds became scarce, culture of those species amenable for husbandry were started.
It is not exactly known when culture practices started. At present, widespread and indiscriminate exploitation coupled with the invading and harmful effects of increasing coastal communities and industries have greatly reduced the available supply for these desirable resources. Unless expansion to more remote areas and intensification of production through improved methods of culture are adopted, the supply for this commodity will continue to deteriorate. At the same time, efforts should be exerted to same some of the natural areas as natural sources or sanctuaries for the species used in culture operations.
The country's shellfish production has fluctuated widely between 50 000 to 290 000 tons per year. This very wide variation is indicative of either the unreliability of data or the big influence of the varying annual weather conditions in the country. We can, therefore, consider the data on hand as preliminary and indicative only of the trend in the shellfish production in the entire country. As shown (Table 1, Fig. 2), the shellfish production gradually increased from 50 000-ton level to a peak of 290 000 in 1971. Since then, the production declined abruptly until it dropped to the 50 000-ton level in 1974. It was that very low level during that year that probably triggered the need for the raising of the cultivable species.
The major species produced in the order of their estimated tonnage in 1975 are: green mussel (Mytilus smaragdinus) with a tonnage of 46 000; horse mussel (Modiolus senhausenii) with a tonnage of 30 000; carpet shell or short-necked clam (Paphia undulata) with a tonnage of 14 000; cockle (Anadara granosa) with a tonnage of 6 000 and oyster (Crassostrea commercialis) with a tonnage of 5 000. There are other minor species which give a combined tonnage of 5 000. All the major species produced came from natural waters and all, except the short-necked clam, has also been an object of culture operations. It is established that 25 to 90 percent of the production of mussels, cockles and oysters come from culture operations (Table 2).
Latest estimates of the Department of Fisheries show that there are about 5 000 hectares (Table 9) presently devoted to shellfish culture in the entire country. Most of these are used for mussel culture and some for oyster and a little portion for cockle. It is estimated that there are over 60 000 hectares of suitable areas that could still be developed for shellfish farming distributed in different coastal provinces in the country. The most extensive areas are located in Trat, Pangnga, Chanthaburi, Ranong, Surat Thani, Samut Sakhorn and Samut Prakharn.
Recent culture practices are traditional which have been developed by people living in the sites suitable for shellfish farming. Mussel and oyster culture originated from gathering of these shellfish from the stakes of abandoned fixed fish traps. Subsequently, bamboo poles and palm trunks were used as stakes for this purpose. Bottom culture of cockles and, to some extent, mussels are also used. Rock culture of oysters using either artificial or natural rocks, is being practiced. It can be seen that many improvements can be introduced to increase and make production more efficient.
Thailand has very high potential for large increase in shellfish production. The production of green mussels can be extended from the present hectarage of 2 500 to 35 000 ha; horse mussel from 300 to 5 000 ha; cockle from 500 to 11 000 ha; and oyster from 1 000 to 13 000 ha (Table 10).
It is estimated that the production in 1976 is about 140 000 tons from the 5 000 hectares shellfish farming areas of the country. On full development to over 60 000 hectares of suitable and available sites for shellfish culture in addition to areas presently used, the country is capable of producing close to 2 million tons of shellfish or an increase of over 1 000 percent.
A programme for the development of the country's potential for shellfish production will therefore be very rewarding. This could be accelerated if given the required support. However, such a programme should include studies on processing, product development, quality control and marketing of shellfish products. Such a programme should include technical, financial and institutional support for the balanced development of production.
