Oysters, the familiar bivalve molluscs so sought after by the world's gourmets, can be found in many parts of the world. They prefer an ocean bottom environment, particularly in inlets where the water is shallow and warm. In Taiwan, the oyster beds stretch from Hsiangshan in Hsinchu County in the north, to Tungkan in Pingtung County in the south, along the island's west coast. The history of oyster culture in Taiwan stretches back over 200 years.
In the Taiwan Strait, where the tidal range is great, oyster farmers have traditionally arranged bamboo stakes in circles or parallel rows along the exposed sandbanks, enclosed within fences. This traditional method is still used by many oyster farmers, particularly at Lukang. It is not, however, regarded as ideal, since during ebb tides, the oysters are exposed to the sun and air for long periods at a time. As a result, the young oysters are only able to eat at irregular intervals, and their growth is stunted. In addition, the bamboo stakes are arranged so closely together that the loose shifting sand and mud sometimes smothers them. Hsiangshan is a typical example of a fishing village which suffers from this problem.
T. C. Yu, head of the Lukang Fishery Center has led the way in promoting oyster culture in Taiwan. Through his 30 years experience in fishery research, Yu was able to introduce what are known as "restraint spats" to oyster fishermen in Hsiangshan. After collecting the oyster eggs laid around August and September, he exposes them to the sun, and then the wind and sea, at alternate intervals to slow down their growth. In this way, he was able to produce a strain with great strength and vitality, which when transplanted, would survive even the harshest conditions. The young oysters then attach themselves with a limy secretion from their left mantle folds, to plastic cords strung horizontally or vertically from a bamboo dredge supported by stakes. This new approach to oyster farming has brought great prosperity to the oyster farmers of Hsiangshan.
Yu used a different approach to solve the problems encountered by the oyster farmers at Putai in Chiayi County. Because the coastal waters there are comparatively deep, Yu recommended farmers to use the "buoyant barrel" method. Under this system, the barrels support the bamboo dredges, and as they move with the changes in the tides, they provide the young oysters with fresh feeding areas, thus enabling them to grow at a fast rate. This method also reduces the risk of attacks from pests such as the oyster-drill snails, and damage from polluted water. But farmers have to take special precautions to prevent damage to the barrels from typhoons which attack the island frequently. The biggest battle of all, however, is undoubtedly against pests, of which the oysterdrill snail is the most destructive. This creature, enclosed in a beautiful spiral shell about an inch long, has a tongue coated with cutting barbs with which it drills a hole through the shell valve and kills the oyster inside. To counter this menace, the farmers must periodically lift the oyster dredges out of the water and shake them violently or spray them with water so that the snails fall out.
Yu said that three factors influence the growth of the young oysters: The nature and amount of food supplies; the temperature of the water; and its relative salinity. Oysters feed upon all kinds of minute organisms, both plant and animal, which float in the water, but the bulk of their diet is made up of the tiny shell creatures known as diatoms.
In Taiwan, oysters are usually not sold while still in their shells, and thus the oyster shuckers must show great skill in order to complete their work in time. To open the shell, the shucker places the live oyster against a chisel edge and then taps it with a hammer. This makes it easy to prise the shell open with a knife, cut the adductor muscle which attaches the oyster, remove the soft flesh and prepare it for market.
Because of the limited production of oysters in Taiwan, there is none left over for export. But the potential for exports of oyster eggs is promising. In 1974, a trial order of several million spats was placed by Japanese interests, and their growth rate was found to be twice as fast as that achieved by indigenous Japanese type. A second set of spats will be exported in March, and if they prove as successful, regular orders can be expected in the future.
