Aquaculture:

Farming of the ocean is called aquaculture. Aquaculture will be an important source of food production. It involves developing and raising special breeds of marine animals and plants that yield large amounts of food. Aquaculture has been used to successfully grow shrimp, salmon, catfish, and oysters on large aquatic farms. A method that might be used to breed other fish and shellfish in ocean waters. A major problem for the aquaculturalists is the farms would be susceptible to pollution and may themselves be a local source of pollution. Ocean farms can produce more valuable protein-rich food than a land farm of the same size.
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www.noaanews.noaa.gov and From the Book of Modern Earth Science