The term blue revolution refers to the remarkable emergence of aquaculture as an important and highly productive agricultural activity. Aquaculture refers to all forms of active culturing of aquatic animals and plants, occurring in marine, brackish, or fresh waters.
Aquaculture has long been practiced in China and other places in eastern Asia, where freshwater fish have been grown as food in managed ponds for thousands of years. In recent decades, however, the practice of aquaculture has spread around the world. Many species of freshwater and marine organisms are being cultivated as highly productive and nutritious crops for consumption by humans. The tremendous growth of aquaculture has been stimulated by knowledge that there are intrinsic limitations to the productivity of the wild, unmanaged aquatic ecosystems that humans have traditionally exploited as sources of fish, aquatic invertebrates, and seaweeds. Moreover, in a depressingly large number of cases, the usable productivity of natural aquatic ecosystems has been overexploited or otherwise degraded by humans, and the harvested yields have declined substantially.
In many cases, however, the productivity of valuable aquatic species can be greatly increased under managed conditions, and also by genetic selection for varieties having desirable traits, such as higher productivity. The principal goal of aquaculture science is to develop systems by which aquatic organisms can be grown and harvested at high but sustainable rates, while not causing unacceptable environmental damage.
Aquaculture production
Aquaculture accounted for over 40 million tons of global fish supplies in 2005. When aquatic plants are included, the figure goes up to 51.4 million tons. The countries of Asia contribute over 90% of these figures. China, by itself, contributes more than 70%. These amounts have far exceeded earlier years. For example, aquacultural activity in Asia was 16 million tons of production in 1995, compared with 1.5 million tons in Europe, 0.46 million tons in North America, and 0.60 million tons in the rest of the world. As of 2006, the top ten species of fish caught with aquaculture are (in order of total amount): carps and other cyprinids; oysters; miscellaneous marine mollusks; clams, cockles, and arkshells; salmons, trouts, and smelts; tilapias and other cichlids; mussels; miscellaneous marine crustaceans; shrimps and prawns; and scallops and pectens.
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In comparison, the global supply of fish in 2004 was about 135 million tons. Thus, aquaculture contributes about 30% to fish production worldwide. Clearly, aquaculture is an extremely large and rapidly growing enterprise.
Fish farming
Fish farming is a relatively intensive enterprise. It commonly involves the management of all stages in the life cycle of the cultivated fish, from the production of eggs and larvae, through to growth and eventual harvest of high-quality, market-sized fish. In this sense, fish farming is different from fish ranching, which is a less-intensive enterprise that usually involves the confinement and feeding of captured wild fish in order to increase their market value. This is done, for example, with bluefin tuna (Thunnus thynnus ) in some places.
Fish have many potential benefits as cultivated species. Because they are cold-blooded (or poikilothermic ), fish divert little energy to maintaining their body temperature, and can therefore convert a relatively large proportion of their food into their growing bio-mass. In other words, populations of fish can be very productive, especially under conditions where the animals are well fed and the rates of mortality from disease and predation are kept small. Moreover, fish are a tasty and highly nutritious food for humans. Consequently, the economic value of fish is great, as are the potential profits gained from cultivating them in large quantities.
Various species of fish are grown in aquaculture, using a variety of cultivation systems. The systems most commonly involve confinement in artificial ponds, or in cages set into larger bodies of water, including the ocean. The fish are fed with a nutritious diet, sometimes to excess so that their growth rate is maximized. When the fish are economically mature, they are carefully harvested and processed so that the highest-value economic products can be delivered to consumers.
The oldest fish-farming systems were developed in eastern Asia, and involved several species of freshwater fish. The first writings about methods of fish culture are dated from about 2,500 years ago and were written by Fan Lei, a wealthy Chinese fish farmer. The first species to be grown in aquaculture was probably the common carp (Cyprinus carpio ), a species native to China but now spread throughout the world. It is still an extremely important species in aquaculture. Other so-called Chinese carps are also important in Asian fish farming, including the grass carp (Ctenopharyngodon idella ), bighead carp (Aristichtys nobilis ), and silver carp (Hypophthalmichtys molitrix ). Other prominent species are tilapia (Tilapia mossambica and other Tilapia species) and Asian catfish (Clarias spp.).
Freshwater fish are also cultivated in North America and Europe. Most commonly grown are species of trout, especially brook trout (Salvelinus fontinalis ) and rainbow trout (Salmo gairdneri ). Also important are channel catfish (Ictalurus punctatus ), and the common carp.
Fewer species and quantities of fish are grown under brackish-water conditions in Asia, but they include the milkfish (Chanos chanos ). Brackish and saltwater fish farming are larger enterprises in northern Europe, North America, and western South America, and New Zealand, where species of trout and salmon are commonly cultivated, sometimes in large, open-water complexes of cages supported by rafts. Especially important species are Atlantic salmon (Salmo salar ), brown trout (S. trutta ), and Pacific salmon (Oncorhynchus spp.).
Invertebrate culture
Many species of mollusks, crustaceans, and other invertebrates are grown in aquaculture, particularly in Asia, but increasingly in other regions as well.
The most important crops are mollusks, especially species of oysters (Crassostrea spp.) and mussels (Mytilis spp.). Most crustacean production occurs in Asia, where species of oriental shrimps are cultivated (Penaeus spp. and Metapenaeus spp.), along with giant freshwater prawn (Macrobrachium rosenbergii ). In Europe and North America, attention has focused on American and European lobsters (Homarus americanus and H. gammarus ), and on various species of crayfishes.
Seaweed culture
Seaweeds are also grown in large quantities for use as food and as feedstock for the production of alginates and other industrial products. Most aquaculture production occurs in Asia, although there is also a growing industry in North America.
Environmental impacts of aquaculture
Aquaculture provides many benefits to people, mostly through access to a large production of nutritious, high-quality foods. However, as with terrestrial agriculture, there are adverse environmental impacts of aquaculture.
The most important effects are ecological, and are associated with the conversion of natural ecosystems into intensively managed aquacultural ecosystems. For example, the conversion of tropical mangrove forest into aquacultural facilities for the raising of shrimp or prawns results in an extensive loss of natural habitat. This conversion has important consequences for native species, and it may damage offshore ecosystems through increased rates of siltation and pollution. In addition, aquaculture operations often degrade local water quality in various ways. Oxygen concentrations may be lowered to unacceptably small concentrations because of the consumption of this gas during the decomposition of waste feed and animal feces. Other impacts are associated with toxic chemicals that are applied to aquaculture cages in order to prevent them from being colonized or eaten by marine organisms. Local waters and species may also become contaminated with antibiotics and other medicines that may be used to keep animal crops healthy. In addition, non-native species may escape from aquaculture and establish themselves in new habitats, possibly competing with or degrading the habitat of native species.
These and other environmental effects of aquaculture are important considerations. They must be dealt with effectively if aquaculture is to be conducted as a sustainable enterprise, in the ecological sense.
See also Trout-perch
Resources
BOOKS
Jana, B.B., and Carl D. Webster, eds. Sustainable Aquaculture: Global Perspectives. New York: Food Products Press, 2003.
Lucas, John S. and Paul C. Southgate. Aquaculture: Farming Aquatic Animals and Plants. Oxford, UK: Fishing News Books, 2003.
Pillay, T.V.R. Aquaculture and the Environment. Oxford, UK, and Ames, Iowa: Blackwell Publishing, 2004.
_____. Aquaculture: Principles and Practices. Oxford, UK, and Ames, Iowa: Blackwell Publishing, 2005.
Stickney, Robert R. Aquaculture: An Introductory Text. Oxfordshire, UK, and Cambridge, MA: CABI Publishing, 2005.
Bill Freedman