CHINA

Current status

Bivalve culture in China has a long history and currently it occupies an important position in modern mariculture.
Several species of edible oysters are found in Chinese coastal waters, however only Crassostrea plicatula and C. rivularis are cultured on a large commercial scale. Small-scale culture of C. talienensis is practised in Liaodong and Shandong peninsulas. The C. plicatula culture is mainly in Fujian and Zhejiang and C. rivularis in Guangdong (Table 3 and Fig. 3).
Oyster production data are available from 1983 (Figure 4). There has been an average annual growth rate of 15.9% from 1983 to 1986 with the highest growth rate of 25.0 % from 1984 to 1985. The area under cultivation in 1983 was estimated to be 24,886 hectares. In 1986 it has reportedly increased to 36,880 hectares with an annual growth of 16.1 % (Tong, 1987).

Culture practices

Spat of C. plicatula and C. rivularis are produced all year round with peaks from May-September for the former and from June-August for the latter.
Several materials are used as cultch and oysters often remain on them until they have attained marketable size. In Guangdong, traditional type of cultches are 3–8 kg stones, ceramic pieces, tiles or large oyster shell. The above oysters are all inexpensive and easy to handle, however their major disadvantages are that they provide a limited surface for settlement and tend to sink in soft mud. These materials have been mostly replaced by cement cultches. Two kinds are in use, the cement bar and the cement tile, both of which tend to remain on the surface of the mud. In Fujian, bamboo stakes and stones are used as spat collectors.

Several culture methods are being practised in China.

Bottom method. The oyster C. rivularis is cultured mainly on the bottom of estuaries of low salinity. A number of cultches are typically used such as gravel, cement plates, cement bars and oyster shells. As many as 30,000–38,000 cement bars and 100,000– 140,000 cement plates are laid down per hectare.
The growth period ranges between 7–12 months and yields vary from 30–80 t/ha.

Stake method. In the northern and eastern parts of Fujian, the bamboo stake is the typical culture method adopted (Fig. 5). The coastal areas in these regions tend to be soft and muddy. Stakes 1.2 m long and 1.5 cm in diameter are laid down in bundles (4–5 stakes/bundle) in mid-tidal flats just before the spatfall peaks. The bundles are regularly spaced in rows. Usually 150,000– 180,000 stakes per/ha are used as collectors, however this number decreases during the culture period due to the thinning operation carried out once or twice a year.
The spats settling in May reach marketable size in 11–15 months, and those in September, 16–18 months. Yields vary from 60–110 t/ha.

Stone-bridge method. This method is prefered for sandy muddy bottoms and is extensively practised in the southern part of Fujian. Bridges made of stone bars measuring 80×20×8 cm are used to collect spat on mid-tidal flats in May and June (Fig. 6). Usually an average of 15,000 stone bars are laid per hectare. Growth period ranges from 7–12 months and yields vary from 30–80 t/ha.

Raft method. The raft method has been recently introduced, especially in South China, where potential damage by typhoons has limited oyster culture to the traditional bottom method. Raft culture is becoming increasingly important, mainly due to the fact that higher yields in a shorter period are obtained when compared to bottom culture. An 84 m² raft produces the same yield in 2 years as 667 m² of bottom culture does in 4 years (Nie, 1982). In addition, well constructed rafts tend to withstand heavy action of waves and wind.

Problems and constraints

The oyster industry in China is well developed, however, some degree of mechanization will be required if output is to be increased.
Oyster culture in the southern coasts of China has been limited to the traditional bottom culture mainly due to potential damage by typhoons. However, during the last few years experimental raft culture has been introduced.

Future plans

There are more than ten institutes in China involved in mariculture research and most of them are currently carrying out some research to improve oyster culture.
Although China stands as the world's third biggest fishery nation with a total fisheries production of 8,235 million MT in 1986, its population of 1,046 billion makes per caput consumption of fish lower than the world average. In 1986, the annual yield of mariculture was 857,592 MT from an area of about 325,000 hectares. Mariculture production is expected to increase at an annual rate of more than 10% during the period 1986–1990 to reach 1.2 million MT in 1990. The area devoted to mariculture will be expanded to 600,000 hectares. Among commercially important seafarming species, bivalves are certainly the major group in terms of annual production. Of the total 1986 national mariculture output, as shown above, 539,656 MT (62.9%) were from bivalve species, mainly from mussels (Mytilus edulis), razor clam (Sinonovacula constricta), hard clam (Veneridae sp.) and oysters (Crassostrea spp.).
Experimental culture trials are being carried out on other cultivated oyster species including the Pacific oyster,
Crassostrea gigas. The aim of the oyster culture industry in China is to increase output for local consumption and the export market.

Table 3. Distribution and main culture areas of commercially important oyster species in China.

Figure 3: Major farming provinces of the three commercially important oyster species in China.

Figure 4: Oyster production data in China from 1983 to 1986. (Source: Tong, J., 1987).

Figure 5: Bamboo stake culture method.

Figure 6: Stone-bridge culture method.