Proceedings of the Symposium on Costal Aquaculture

Culture of seaweeds is practiced since ages in countries such as Japan, Ctiina and Korea. Seaweed cultivation is an industry in Japan as a part-time avocation for land farmers and fishermen. The seaweeds cultured mainly in these countries are Porphyra, Undaria, Laminaria, Enteromorpha and Monostroma. In India seaweed culture is yet to develop on commercial lines. While the demand for these seaweeds is for food purposes in foreign countries, their demand in India is for the extraction of two phytochemicals namely agar-agar and algin. In recent years many factories manufaauring these chemicals have come up in India as a consequence of which the demand for the agarophytes and alginophytes has gone up. In order to maintain a continuous supply of this raw material to the industry, methods to augment the supplies through culture practices have to be developed.

In recent years the Central Marine Fisheries Research Institute has been engaged in the cultivation of several economically important seaweeds such as Sargassum wightii, Twbinaria spp., Gracilaria edulis, G. corticata and Gelidiella acerosa which indicated great scope for cultivation. The production rate has been found to be 4.4 kg/m' in the case of G. edulis and 3 kg/m* in the case of G. acerosa in about 80 days for 0.30 kg and 1 kg of seed material introduced respectively. In the case of alginophytes the growth was not encouraging. These culture experiments were conducted by introducing small fragments of the seaweed into the twists of the coir ropes fabricated in the form of a S x 2 m net and tied to fixed poles in inshore waters. In the case of G. acerosa, the substratum along with the plant fragments was tied to the ropes.

The agarophytes thus grown can be processed further for extraction of agar-agar. The extraction could be done by a simple cottage industry method not involving any costly equipment. In the case of Gelidiella agar, freezing and thawing are required to remove the insoluble chemicals. A total of 90 tonnes of G. edulis can be obtained from 3 harvests in a year from a hectare area.