Encyclopedia of Food & Culture | Aquaculture

AQUACULTURE. Aquaculture, the controlled or semi-controlled production of aquatic plants and animals, has increased at double-digit percentage rates since the early 1980s. This increase has been in response to declines in commercial harvests of wild stocks of fish and shellfish. Oceans of the world are currently at maximum sustainable yield. Since the late 1980s, there has been a concerted effort to maintain global commercial harvest of ocean fish at approximately 100 million metric tons (mmt). However, as global population grows, demand for fish and shellfish increases, and the percentage of aquatic products grown in aquaculture must likewise rise to meet the supply of those products. Projections for increased production are in the range of 40–100 mmt of new aquaculture production by about the year 2030. The lower range assumes only increases in world population; the upper figure represents increases in world population plus a 1 percent per year increase in per capita consumption. To put this number in perspective, the 1995 world production figures for soybeans was 137 mmt, swine was 83 mmt, and chickens was 46 mmt. Thus, to meet demand in the first part of the twenty-first century, we must realize significant growth. This increase in production will not be accomplished with a single species.

There are fewer than thirty large species-specific aquaculture industries globally, and the fourteen largest industries are listed in the table. However, there are over twenty-five thousand species of fish and there are estimates that one thousand new species are being evaluated for their culture potential. The small percentage of species raised relative to the total number available is an indication that aquaculture is a new concept in many parts of the world. As a subsistence enterprise, aquaculture has been practiced for over four thousand years. As a series of large industries, aquaculture is less than fifty years old, often stimulated by declining wild stocks of fish. The channel catfish industry, which only began in the late 1960s in the southern United States, is illustrative of a relatively young industry. Today, over 90 percent of the U.S. supply of Atlantic salmon is cultured. In 1980, that figure was a fraction of 1 percent, at most. The global supply and demand characteristics created a good deal of volatility in production, which has only increased over time. Additional factors such as identification of new

The largest aquaculture industries, by volume, in 1999
Values are in million metric tons
Species	Volume
Giant tiger prawn	3,651,782
Pacific cupped oyster	3,312,713
Japanese kelp	3,023,240
Silver carp	2,837,420
Grass carp	2,743,194
Atlantic salmon	2,448,280
Japanese carpet shell	2,194,521
Roho labeo	1,493,884
Rainbow trout	1,350,168
Japanese amberjack	1,282,090
Yesso scallop	1,252,448
Nori	1,249,923
Whiteleg shrimp	1,062,774
Nile tilapia	1,025,739

diseases and movement of those diseases contribute to the volatility in production. Inevitably, as new aquaculture species are brought into culture settings, new diseases are identified that were previously unknown. In the past ten years, new viral diseases have been identified in shrimp and salmon, both of which caused large-scale losses from production facilities.

Of the approximately 25 mmt of global aquaculture production, there are only a few industries that produced over 1 mmt in 1996. Several of the species of Asian carp and the common carp account for the largest industries. Silver carp production was 2.2 mmt, grass carp production was 1.8 mmt, bighead carp production was 1.1 mmt, and common carp production was 1.5 mmt. Virtually all of this production occurred in China with the exception of common carp, which is raised throughout Europe, its native range. Of the species typically available in U.S. markets, pen-raised Atlantic salmon accounted for 0.4 mmt, rainbow trout production for 0.3 mmt, channel catfish production for 0.2 mmt, and tilapia for 0.6 mmt. Production of several invertebrates was significant. Scallop production was 1.0 mmt, shrimp production was 0.9 mmt, oyster production was 1.1 mmt, mussel production was 1.0 mmt, and clam production was 1.0 mmt. Production of brown seaweeds was 4.5 mmt and red seaweed production was 1.6 mmt. Thus, the largest aquaculture industry is the production of brown seaweeds, largely for nonfood use. In the twenty-first century, greater demand will likely result in increased production.

There are only a few production systems in use for aquaculture, and they include earthen ponds, raceways, cages or net pens, and indoor recirculating systems. Earthen ponds or cages placed in existing bodies of water are the oldest production system and the indoor recirculating systems are the newest. For successful culture, considerable technical expertise is required when using a recirculating system. All of the current industries use earthen ponds (catfish, tilapia, Asian carps, shrimp), raceways (rainbow trout), or cages/net pens (Atlantic salmon, yellowtail, an amberjack from Southeast Asia). Producers are experimenting with indoor recirculating systems using a wide variety of species. There are a few successful producers using indoor systems, but the number will inevitably grow as both the systems themselves and information on targeted species increase. Successful aquaculture can be viewed as the correct match of species under a certain set of market conditions with production system. Some species do not tolerate some of the production systems or do not thrive in those systems. Behavioral characteristics of the various species often point toward the appropriate culture systems. For example, sedentary fish (bluegill, catfish, and flounder) should probably be raised in systems without significant water flow (earthen ponds, cages/net pens), whereas those that typically swim a great deal (tuna, trout, and striped bass) can be raised in raceway systems with a constant flow of water.

Fish are generally considered good quality food for human consumption because of the low saturated fat levels and generally high levels of n-3 fatty acids. Fish tend to retain the fatty acids that are in their diet. Thus, we can manipulate the fatty acid concentrations of fish and produce "designer fish" for targeted markets. Further, we can control the fat concentration in muscle through selected feed and produce a low-fat or high-fat fish depending on the demands of the market. Cultured aquatic animals can be safer products for consumption than wild fish because they are raised in a defined environment, and pollutants can be eliminated. Wild fish can be exposed to environmental pollutants and retain those they encounter. Organoleptic properties (taste) of fish and shell-fish raised in aquaculture can be quite different from wild stocks. Fish flavor can be manipulated by dietary ingredients fed to the target species. If the diet contains a relatively high percentage of fish meal, the fish can taste fishier than if the diet contains a relatively high percentage of corn and soybean products. Fish fed the latter diets are often described as "milder" tasting, which is a desirable characteristic in certain markets. There is also a taste consideration with environment. Some species can survive both fresh-and saltwater, but osmoregulation changes to meet the challenges of those environments. This physiological change affects taste because of the chemical compounds used to regulate ionic balance. A good example of this is the freshwater shrimp. When raised in freshwater, taste has been described as mild, whereas if the shrimp is placed in saltwater for one to two weeks, it will taste more like a marine shrimp. Even with these positive attributes, aquaculture is experiencing growing pains.

Culture of aquatic animals produces the same wastes as other animal production industries. The problem is confounded by the fact that those wastes are discharged as rearing water is renewed. There have been incidences of environmental degradation resulting from aquaculture. One of the focal points of aquacultural research is waste management, focusing on phosphorus and nitrogen dynamics originating in the diet. Those efforts, as well as efforts related to siting aquaculture operations, land-use practices, and economic development, have become the focal point of sustainable aquaculture development. Along with the overall focus on sustainability, there are significant concerns about the feed used to achieve aquaculture's successes. Fish meal is a high-quality ingredient, yet it is a finite resource similar to all other species in the oceans. Ingredients made from soybeans, corn, canola, wheat, legumes, peanuts, and barley, as well as the by-products of the brewing industries and animal packing operations, are needed.

Growth of aquaculture in the twenty-first century will most likely be similar to growth in terrestrial animal production seen in the twentieth century. Fish and shell-fish are the last major food item humans still hunt and gather from wild populations. The sustainable nature of aquacultural production probably will be the focal point of research in the early part of the twenty-first century and those results should facilitate the production increases necessary for sufficient quantities of fish and shell-fish in the future.

See also Crustaceans and Shellfish; Fish, subentries on Freshwater Fish and Sea Fish.

Paul B. Brown