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Fisheries > Culture Fisheries > Edible Oysters

Grow-out Phase

The farming of the oyster in the field comprises nursery rearing of the spat and growing the oysters for market

Selection of farm site

For site selection several factors are to be considered, namely water depth, bottom characteristics, protection from wave action, tidal flow and height, turbidity, water quality including chemical parameters, predation, fouling, pollution and accessibility. It is also important to consider the species and the method of culture. Sheltered areas offering protection from strong wave action are preferred. From intertidal region to areas extending up to about 5 m depth can be considered for adopting suitable culture method. Similarly the culture technique is adopted depending upon the type of substratum. On-bottom culture method is substrate-specific while off-bottom method has little to do with the nature of substratum. Salinity range of 22 to 35 ppt is suitable. The natural populations occur at a temperature range of 21 to 31oC.

Nursery rearing of spat

For nursery rearing relatively calm waters with adequate flow to bring phytoplankton are preferred. In many cases a part of the oyster farm is used as nursery. Special nursery ponds in the inter-tidal region are also constructed. The oyster spat taken out of the hatchery are too small to be grown in the field without protection. They are enclosed in velon screen bags of suitable mesh size and suspended from racks. A string can hold six shell valves containing 80-100 spat and 3 to 4 strings are enclosed in a bag. The bags are periodically cleaned and after 40 to 50 days they are transferred to the farm.

Culture Management

Cultured oysters require a level of care to ensure their continued survival and growth to marketable size. Farm management includes cleaning, thinning, sorting or grading, pest control and predator protection.

Cleaning: Washing the oysters, either with a pump or swishing the trays up and down in the water removes silt and other dirt. A pump is preferable, since it can also remove newly attached fouling organisms and is fast, saving labour. Should fouling be heavy, brushing may be required. The frequency of cleaning depends on local conditions. If siltation is heavy, monthly washing may be necessary. Normally, siltation is not much of a problem during the dry season.

Thinning: Oyster spat may be nursed at high density, but upon reaching around 3 cm length, they should be thinned out to the final grow-out density. If the oysters are overcrowded, growth is very slow and mortality increases rapidly. Oysters should be sorted so that each tray contains more or less the same sizes. The sorting process continues until oysters are marketed. Sorting also reduces labour at harvest time, as only those trays with marketable oysters need be selected for harvest.

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