Since the 1970s, the practice of aquaculture has been the focus of a worldwide surge of interest and has been growing at an annual rate of more than 7%. Today, the sector produces almost 50 million tons of fish, shellfish, and crustaceans annually, making up a third of all fish products to reach the market.
Unfortunately, aquaculture generates the same sorts of problems as any other form of intensive breeding: it produces organic and nitrous waste, as well as chemical waste (antibiotics and fungicides), and the concentration of living organisms is associated with increased risk of disease. But does it at least help to ease the pressures on wild fish? Not always, by any means. Shrimp, for instance, are usually farmed on sites that have been cleared of mangroves which previously provided a habitat for numerous species of marine life. And fish farming often focuses on the large carnivorous species particularly favored by consumers: salmon, sea bream, and turbot, for example. These predators require the inclusion of certain amino acids in their diet that are only to be found in fish and fish derivatives such as meal. It is estimated that between 2.5 and 5 lb of wild fish are needed to produce 1 lb of carnivorous farmed fish.
Happily, plant-eating fish can be farmed too. These often live in freshwater and not only pose fewer challenges in terms of farming, but could also provide human beings with precious supplies of animal proteins in years to come. Whereas 7 lb of cereals are needed to produce 1 lb of beef, 2 lb of grain are enough for 1 lb of carp, tilapia, or catfish. In China, a great many small-scale farmers have incorporated aquaculture into a highly efficient system of polyculture, using liquid pig manure, for example, to increase the production of algae in their ponds, which in turn makes their carp grow more rapidly. The promising practice of breeding fish in rice plantations (rice being the world’s most widely grown grain) is also increasing.