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fattening, and harvesting. The spawning and spat fall has been described by Mok, 1973. The minimum water temperature and highest salinity recorded in Deep Bay studies for minor spawning were 25.8°C and 19.5 g/kg respectively, and for mass spawning greater than or equal to 27.4°C and less than 14.9 g/kg. Spawning occurred from May to September with setting or spat collection between June and October, (Mok, 1973).
The views of Chinese oyster farmers were that water temperature from 21°C to 30°C and salinity 10 to 15 g/kg were necessary for spat fall, together with an appropriate wind direction. It is doubtful whether the wind has any direct significance, but the hydrography is influenced by wind and appropriate salinity levels and other factors referred to in basic literature on oysters are thus affected by wind vectors. Collection of spat was considered best in May and June for around 40 days only. Technicians from a research and culture station in Shekou considered the best period to be shorter, limiting it to about 20 days in May only. Cultch placed too early would be fouled with barnacles and other biota.
The cultch techniques are discussed in a later section. The typical growth period to achieve market size for Deep Bay oysters has been reported as 5 years, (Mok, 1974a). The life span of the oyster is about 7 years depending on growth rates, (Bromball, 1958). The Chinese oyster farmers consider 4 years as the average time to reach maturity and market size. The Hong Kong oyster farmers interviewed in 1984 indicated that 5 to 7 years is needed in Deep Bay depending on the area of culture. Figure 4 shows the relationship of length of growth period to area of culture suggested by the farmers. The farmers claim that the increased growth period is a result of increased pollution, but there is no direct evidence to support the claim. Neither are adequate hydrographical or chemical data available to examine whether some natural phenomenon is responsible. The Chinese farmers interviewed did not mention the problem.
The fattening process only takes a few months during the autumn prior to the main winter sales season. In the summer months the flesh is lean and watery as a result of the stress due to production of sperm and eggs but subsequently becomes thick and
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fattening, and harvesting. The spawning and spat fall has been described by Mok, 1973. The minimum water temperature and highest salinity recorded in Deep Bay studies for minor spawning were 25.8°C and 19.5 g/kg respectively, and for mass spawning greater than or equal to 27.4°C and less than 14.9 g/kg. Spawning occurred from May to September with setting or spat collection between June and October, (Mok, 1973).
The views of Chinese oyster farmers were that water tempera- ture from 21°C to 30°C and salinity 10 to 15 g/kg were necessary for spat fall, together with an appropriate wind direction. It is doubtful whether the wind has any direct significance, but the hydrography is influenced by wind and appropriate salinity levels and other factors referred to in basic literature on oysters are thus affected by wind vectors. Collection of spat was considered best in May and June for around 40 days only. Technicians from a re- search and culture station in Shekou considered the best period to be shorter, limiting it to about 20 days in May only. Cultch placed too early would be fouled with barnacles and other biota.
The cultch techniques are discussed in a later section. The typi- cal growth period to achieve market size for Deep Bay oysters has been reported as 5 years, (Mok, 1974a). The life span of the oyster is about 7 years depending on growth rates, (Bromball, 1958). The Chinese oyster farmers consider 4 years as the average time to reach maturity and market size. The Hong Kong oyster farmers interviewed in 1984 indicated that 5 to 7 years is needed in Deep Bay depending on the area of culture. Figure 4 shows the relation- ship of length of growth period to area of culture suggested by the farmers. The farmers claim that the increased growth period is a result of increased pollution, but there is no direct evidence to support the claim. Neither are adequate hydrographical or chemi- cal data available to examine whether some natural phenomenon is responsible. The Chinese farmers interviewed did not mention the problem.
The fattening process only takes a few months during the au- tumn prior to the main winter sales season. In the summer months the flesh is lean and watery as a result of the stress due to produc- tion of sperm and eggs but subsequently becomes thick and
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