The growing of plants and animals on land for food and other products is agriculture. Raising animals and plants in the water is aquaculture. Practised since ancient times in many parts of the world, aquaculture embraces such diverse activities as the Chinese tradition of growing carp in ponds, the harvesting and processing of seaweed in Iceland and the artificial culture of pearls — a Japanese invention. Aquaculture can take place in water that is still or in running water, fresh or salt. The practice of aquaculture has been growing rapidly. Experts have projected a five-fold increase in harvests during the final quarter of the 20th century. In the 1970s, Asia accounted for approximately 85 percent of world production in the field. Aquaculture is regarded as one possible solution to the world's food supply problems. The quantity of tillable land is limited and shrinking everywhere. But two thirds of the globe is covered with water; the supply of food animals and plants that may be grown there is almost limitless. In contrast to agriculture, which is practised on the land's surface only, aquaculture is three-dimensional. Within the same vertical region, several different crops can be grown at once — near the water surface, on the bottom and in the area between. Multiple cropping of this kind, called polyculture, represents an efficient use of labour, materials and energy. Moreover, aquaculture is less affected by climatic change — droughts, floods, and extremes of heat and cold — than is agriculture.
It is clear from the passage that aquaculture ------ .
is most suitable for culturing pearls
is not a newly-found application
has been invented only recently
is currently being practised in very few regions
is the most advanced in Japan
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