Coastal Aquaculture and Mariculture (2+1)

Unit 3 - Methods of coastal aquaculture and mariculture

3.4. Culture methods for oyster, mussels and seaweeds

A. Oysters
On-bottom and off bottom culture are practiced for edible oysters.

1. Onbottom culture: this method of culture is followed on a fairly firm bottom; protected from wave action and predators. Oyster spats are sowed and harvested when grown to marketable size. Though this method is cheaper, siltation over oysters beds can cause problems, and the areas may not always be free from predators.

2. Off-bottom culture: Many methods of off-bottom culture viz., pole/stick method, and raft culture methods are followed.

Pole /stick culture: Wooden or bamboo sticks are installed in rows in shallow muddy regions of the intertidal zones. Sheltered areas free from strong waves and wood boring organisms are selected. Seed oysters are attached to the poles using degradable nets, or sting on which oysters are collected are strewn round the poles for fattening and final harvest.

Raft/string culture: string/trays are suspended from floating rafts or long lines. Raft are use in protected areas, strings in more exposed areas. Rafts/longlines are supported by buoys. Trays are made of wood or wire screens. Spat oysters are placed in trays and suspend for grow out.

B. Mussels
The methods for mussels are very similar to oyster culture. Bottom culture is widely practiced in Germany and the Netherlands; stake culture in France, Italy and the Philippines; and raft and long line culture in Spain.

C. Seaweeds
Raft and long line culture similar to oysters and mussels is practiced for growing seaweeds. Spores are collected on nets from areas rich in spores and they are transferred to on growing areas for culture to marketable size.
Another method of culture is using floating frames, fabricated as nets with ropes of hemp fibres, palmyra fibres or synthetic twines which serve as suitable substrata. The culture frames are suspended in the sub-littoral zone from poles driven into the bottom in such a way that the flat surface of the net is close to water surface even during low tides. Fragments of plants are twisted into the ropes and allowed to grow to harvestable quantity.