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

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 .

BIBLIOGRAPHY

Adelizi, Paul D., Ronald R. Rosati, Kathleen Warner, Y. Victor Wu, Tim R. Muench, M. Randall White, and Paul B. Brown. "Evaluation of Fish Meal-Free Diets for Rainbow Trout, Oncorhynchus mvkiss." Aquaculture Nutrition 4, no. 4 (1998): 255–262.

Donahue, Darrell W., Robert C. Bayer, John G. Riley, Alfred A. Bushway, Paul B. Brown, Russell A. Hazen, Keith E. Moore, and Dorothy A. Debruyne. "The Effect of Soy-Based Diets on Weight Gain, Shell Hardness, and Flavor of the American Lobster (Homarus americanus )." Journal of Aquatic Food Product Technology 8, no. 3 (1999): 69–77.

Floreto, Eric A. T., Robert C. Bayer, and Paul B. Brown. "The Effects of Soybean-Based Diets, with and without Amino Acid Supplementation, on Growth and Biochemical Composition of Juvenile American Lobster, Homarus americanus." Aquaculture 189 (2000): 211–235.

New, M. B. "Aquaculture and the Capture Fisheries—Balancing the Scales." World Aquaculture 28 (1997): 11–30.

Riche, M., and P. B. Brown. "Incorporation of Plant Protein Feedstuffs into Fish Meal Diets for Rainbow Trout Increases Phosphorus Availability." Aquaculture Nutrition 5 (1999): 101–105.

Twibell, Ronald G., and Paul B. Brown. "Optimum Dietary Crude Protein for Hybrid Tilapia Oreochromis niloticus x O. aureus Fed All-Plant Diets." Journal of the World Aquaculture Society 29 (1998): 9–16.

Twibell, Ronald G., Bruce A. Watkins, Laura Rogers, and Paul B. Brown. "Dietary Conjugated Linoleic Acids Alter Hepatic and Muscle Lipids in Hybrid Striped Bass. Lipids 35 (2000): 155–161.

Wu, Y. Victor, Ronald R. Rosati, and Paul B. Brown. "Effects of Lysine on Growth of Tilapia Fed Diets Rich in Corn Gluten Meal." Cereal Chemistry 75 (1998): 771–774.

Wu, Y. Victor, Kerry W. Tudor, Paul B. Brown, and Ronald R. Rosati. "Substitution of Plant Proteins or Meat and Bone Meal for Fish Meal in Diets of Nile Tilapia. North American Journal of Aquaculture 6 (1999): 58–63.

Paul B. Brown

Aquaculture

Aquaculture is the husbandry or rearing of aquatic organisms under controlled or semi-controlled conditions. Stated another way, it is the art of cultivating natural plants and animals in water for human consumption or use. It can be considered aquatic agriculture, or as some people wish to call it, underwater agriculture. It is sometimes incorrectly termed aquiculture. Aquaculture involves production in both fresh and salt water. Mariculture is aquaculture in saline (brackish and marine) water. Hydroponics is the raising of aquatic plants in water. Organisms that are grown in aquaculture include fish, shellfish (crustaceans such as crawfish and shrimp, and mollusks such as oysters and clams), algae, and aquatic plants. More people are eating seafood for their added health benefit. Not only can these organisms be raised for human consumption, but they can also be reared for the lucrative baitfish, health food, aquarium, and home garden-pond industries.

Aquaculture dates back more than 3,500 years ago when carp were spawned and reared in China. There have also been records of aquaculture practices being performed in Egypt and Japan nearly that long ago. Mariculture is thought to have been brought to Hawaii about 1,500 years ago. Modern aquaculture finds its roots in the 1960s in the culturing of catfish in the United States and salmon in Europe.

There are two general methods used in aquaculture, extensive and intensive. Extensive aquaculture involves the production of low densities of organisms. For example, fingerling fish can be raised in ponds where they feed on the natural foods such as phytoplankton and zooplankton , and the matured fish are harvested at the end of the growing season. These ponds can also be fertilized to enhance the food chain, thus increasing fish or shellfish production. Typically, several hundred to several thousand pounds of fish are raised per acre annually. Intensive practices utilize much higher densities of organisms. This requires better water quality , which necessitates circulation, oxygenation, added commercial foods, and biological filters (with bacteria) to remove toxic wastes. These systems can produce more than one million lb of fish per acre (45,000/ha). Intensive aquaculture often utilizes tanks to grow the fish or shellfish, either indoor or outdoor. The water can be recirculated as long as toxic wastes such as ammonia are removed. Some processors run the effluent from the fish tanks through greenhouses with plants raised hydroponically to remove these chemicals .In this way, added revenue is gained. Some aquaculture operations raise only one type of organism (called monoculture ) while others grow several species together (termed polyculture). An example of polyculture would be growing tilapia and catfish together.

About 86% of the world's aquaculture production (about 22 million tons in 1993) comes from Asia. China is the leading producer nation, with most of their production coming from carp, and secondarily shrimp. India is the second largest producer nation, followed by Japan, Taiwan, and the Philippines. For example, 1991 shrimp production in China reached nearly 250,000 tons. (Note: One English ton equals approximately one metric ton, so they can be thought of as equivalents). Only Taiwan exceeded this with 350,000 tons of shrimp produced. Ecuador produced 100,000 tons. In contrast, total shrimp production for the United States was only 1,600 tons. Salmon is another major fish produced by aquaculture, with most coming from Norway. Nearly 300,000 tons were produced in 1990. Great Britain, Canada, Chile, and Iceland are also major producers of farm-raised salmon. Other important aquaculture species and some of the countries where they are raised include: tilapia (Caribbean countries, Egypt, India, Israel, the Philippines); milk-fish (the Philippines); Nile perch (Egypt); sea bass and sea bream (Egypt, Israel); mullet (Egypt, India, Israel); dolphin fish (also known as mahi-mahi; Egypt); grass and silver carp (Israel); halibut and other flatfishes (France, Norway); prawns (Caribbean countries, Israel, the Philippines); mussels and oysters (the Philippines); crabs (India); seaweeds (India, Japan); Spirulina (a blue-green algae; India); and many other examples.

Although people in the United States consume less fish and shellfish than people in other parts of the world, each year we spend billions of dollars importing edible fish. Total production from aquaculture in the United States in 1991 was about 540,000 tons, which earned about $750 million. This comprises only about 3% of the world's total aquaculture production. Domestically, catfish is our major aquaculture species ($200 million per year in 1991). Trout (primarily raised in Idaho) is the number two species raised in aquaculture and accounts for a $55 million per year industry. Shrimp, hybrid-striped bass, and tilapia are other species commonly raised in the United States. Of the 16,000 tons of crawfish (more appropriately called crayfish) collected in 1990 in the United States, about 60% came from aquaculture ponds.

In 1986 the U.S. Congress placed aquaculture under the jurisdiction of the U.S. Department of Agriculture appropriated $3 million to establish four regional aquaculture centers. These centers are located at the University of Washington, Southeastern Massachusetts University, Mississippi State University, and a Center for Tropical and Subtropical Aquaculture jointly administered by the University of Hawaii and the Oceanic Institute. The following year Congress created a fifth center at Michigan State University. The mandate for these centers was, and still is, to promote aquaculture in their region and to solve some of the problems facing this industry. More recent legislation has created mariculture research centers under the Sea Grant Program within the Department of Commerce.

Aquaculture is an appealing industry because it can help supplement what is caught in natural fisheries and what is produced through agriculture. This has tremendous implications in terms of the growing future dilemma with human over-population, decreased fisheries captured from the oceans, and stabilized agriculture production. Aquaculture is a growing industry in the world, which not only translates into more food, but also more revenue and jobs. This fulfills the old Chinese proverb that you can give a person a fish and feed them for a day, or you can teach a person to fish (or do aquaculture) and feed them for a lifetime.

It is particularly important to look at aquaculture development in third-world countries where protein sources are scarce. Since many of these countries lie in equatorial regions, tilapia (also called St. Peter's fish because they are the likely fish caught by the disciples in the Sea of Galilee) are one of the best prospects to grow because of their tolerance of high temperatures and poor water quality (i.e., high ammonia levels). They are also omnivorous filter feeders and thrive on blue-green algae. One alternative to the deforestation of our precious rain forests might be to encourage indigenous people to construct earthen ponds and raise tilapia on the fringes of the forests, thus producing not only a protein source, but also a cash crop . An advantage of aquaculture over agriculture is that fish can be grown in ponds overlying soil that may be toxic to plants (for example, with high concentrations of sulphur, aluminum , or salt). In addition, aquaculture species can often be held longer if there is a glut on the market, thus allowing more flexible selling times. Despite these positive attributes, there are serious problems involved in aquaculture. These include release of waste into the water (adversely affecting water quality); spread of diseases and parasites through concentrated growing conditions; disfavorable taste through chemicals like geosmin in the water being taken up by the fish (termed "off-flavor" in catfish); release of hybrid strains into the natural population which can result in mixed genetics with natural populations; obstruction of the aesthetics along coastlines; and overproduction, which can result in depressed market prices. For example, both the catfish and salmon industries experienced a tremendous drop in their market prices due to overproduction in 1990 and 1991.

Aquaculture seems to have a bright future as long as we address some of the above-mentioned problems. One example of an enterprising solution to one of these problems is that of releasing wrasse (marine parasite-feeding fish) into aquaculture tanks and cages to remove fish lice from salmon. This not only solves the problem of parasites, but also eliminates the need to add chemicals to the water that kill parasites, stress the fish, and pollute the environment . The same pitfalls that have plagued agriculture must be avoided in aquaculture. A key concern is that of sustainability—concern for the culture environment and non-crop organisms in measuring the success of the aquaculture industry (discussed in the June 1996 issue of World Aquaculture ). There is no need for agriculture farmers to feel threatened by aquaculture; on the contrary, it seems that these two areas can actually be brought together, particularly with small local farms in underdeveloped countries supplementing their terrestrial crops with aquatic production. This has already been done quite well in Norway, which has more than 700 fish farms in a country with only 4.2 million people. Aquaculture is evolving from an art, with trial-and-error learning, to more of a science with ongoing research. Countries such as Japan, the United States, Israel, and Norway are developing new technology to bring this field to higher levels. Recent predictions suggest that aquaculture will be able to meet at least 40% of the global demand for fish and shellfish over the next 15 years if current trends prevail. Government, academic institutions, and industry must work hand-in-hand to see that these predictions come to fruition with minimal environmental damage.

[John Korstad ]

RESOURCES

BOOKS

Bardach, J. "Aquaculture." BioScience 37 (1987): 318–19.

Hopkins, J. S. "Aquaculture Sustainability: Avoiding the Pitfalls of the Green Revolution." World Aquaculture 27 (1996): 13–5.

Lee, J. S., and M. E. Newman. Aquaculture Today—An Introduction. Illinois: Interstate Publishers, 1992.

Parker, N. C. "History, Status, and Future of Aquaculture in the United States." CRC Critical Reviews in Aquatic Science. 1 (1989): 97–109.

Stickney, R. R. Principles of Aquaculture. New York: Wiley, 1994.

World Aquaculture Society. "World Aquaculture—A Special Section on Aquaculture Research and Development Around the World." World Aquaculture 27 (1996): 7–30.

Aquaculture

Aquaculture, a type of agriculture, is the practice of cultivating aquatic animals and plants in managed aquatic environments. Aquaculture in salt-water or marine environments is called mariculture. Fish culture, or pisciculture, refers to the husbandry of finfish . The most popular aquaculture species are finfish grown in fresh waters, accounting for over 40 percent of total aquaculture production (U.S. Department of Agriculture, 1998).

Ancient and Modern Aquaculture

Aquaculture has a long history, but for much of the world it remains somewhat of a novelty, being practiced less than agriculture or capture fisheries . Yet as the world demand for fish increases, recent advances in growing fish in captivity have led to a rapid expansion of the aquaculture industry.

During the last 30 years of the twentieth century, aquaculture grew at an average annual rate of 10 percent, and emerged as the only growth sector of the fisheries industry. At the beginning of the twenty-first century, aquaculture's share of total fish production worldwide was 25 percent, and that proportion is projected to increase. Even though the production of fish from capture fisheries has not substantially increased over the past decade (1990s), capture fisheries nevertheless account for a far greater percentage than aquaculture.

Aquaculture's Beginnings.

The roots of aquaculture trace back 4,000 years to China where carp were cultured, and before that to Egypt where early pictorial depictions dating to 2500 b.c.e. show tilapia being fished out of a tank. The earliest known written record of fish culture techniques is attributed to Fan Li, of China, who in 475 b.c.e. described propagation methods, pond construction, and growth characteristics of common carp.

From those early beginnings to the present, common carp is the best understood of all aquaculture species. Common carp reportedly were grown in Europe 2,000 years ago, and, although the ancient Greeks and Romans held fish in ponds, more advanced techniques for breeding and growing fish in managed environments in Europe were first devised 1,000 years ago.

The Japanese, Polynesian Hawaiians, and Mayans were also early practitioners of fish culture. In the United States, nineteenth-century scientists developed techniques for breeding rainbow trout in captivity. Rainbow trout have since been transplanted from their native Western U.S. streams to many countries in Europe, Africa, and South and Central America.

Criteria for Commercially Successful Aquaculture

The twentieth century witnessed the science of fish culture unveiling many new methods for growing aquatic animals and plants. Advances in controlled reproduction of desired species, feed formulation, and water quality management have helped generate the rapid growth of aquaculture. The biological selection of culture species depends on many factors. A few criteria that must be considered in choosing a species to cultivate include the following characteristics of a species:

• Growth rate;
• Place in the food chain;
• Climate and environmental adaptations;
• Disease resistance;
• Breeding characteristics;
• Compatibility with other fish species in cultivation; and
• Conversion efficiency (feed-to-flesh).

For example, aquaculturists prefer fast-growing planktivores because of their short food chain.

Interestingly, biotechnological selection criteria are not always the most critical; for example, growing fish unsuitable for local or export markets can readily drive a farmer out of business. Thus, consumer preference, market conditions, regulations against nonnative species, and other economic, social, and political criteria play an important role in species selection.

Diversity of Aquaculture Species

Hundreds of species of finfish, crustacean , mollusks , and plants are used in aquaculture. Most are finfish species, and many of these are grown asfood fishes . The most common fresh-water aquaculture species are carp, tilapia, catfish, and trout. Other species are cultivated as bait fish , ornamental fish for water gardens and aquaria, sport (game) fish, laboratory fish for experimentation, industrial and medicinal products, and as native fish to mitigate losses to wild fish populations.

In the United States, catfish and trout, grown as food fishes, are by far the most popular aquaculture species. But other species are also commonly grown for food, including salmon, striped bass, and tilapia. Also, there is a small industry for alligators, frogs, turtles, egg seed stock, and ornamental fishes.

Purposes of Aquaculture

Aquaculture is practiced for a number of reasons, chief among them being food production and income generation. Most fresh-water aquaculture production (over 70 percent) comes from low-income, food-deficit countries. Even in the poorest countries, fish farming is seldom solely a subsistence activity. So while farmers may consume some of their product, typically fish are sold, thereby enabling farmers to earn income to purchase other goods and services.

Additional purposes of aquaculture include:

• Utilizing land unsuitable for agriculture;
• Utilizing inland water bodies such as shallow lakes;
• Reclaiming saline soils;
• Increasing the supply of highly valued species;
• Improving the reliability of fish supplied in the marketplace;
• Offsetting losses in the capture fisheries or in native fish populations;
• Servicing the sport fishing industry;
• Controlling parasites like mosquito and snail larvae that cause diseases such as dengue fever and malaria;
• Storing water; and
• Earning foreign exchange. (Europe and the United States import aquaculture products from Asia, Africa, and Central and South America.)

Types of Aquaculture Operations

Aquaculture operations range from small, backyard water gardens to energy-intensive, large commercial farms encompassing hundreds of hectares . Aquaculture is sometimes combined with agriculture as in rice–fish farming, or in duck–fish ponds. It is also practiced as polyculture , where a variety of species occupying different ecological niches are cultivated together. Aquaculture involves many levels of intensity and complexity, from gravity-fed ponds with little or no inputs, to intensive systems that use aeration , supplemental feeds, antibiotics, and genetically modified species.

Systems for rearing fish depend on the environment and the objective of the aquaculture operation. In the United States and worldwide, the most common rearing unit is the pond, although other types of units are also used: cages, net pens , flow-through raceways, and recirculation tanks. Efficient farm management and careful water-quality management are keys to a successful operation, regardless of the culture unit. With poor water quality, for example, fish exhibit higher incidence of disease. In addition, poor water quality often yields effluents (wastewater and byproducts) that can have negative environmental effects.

Potential Adverse Effects

Not too long ago, aquaculture was perceived as a cure for hunger and dwindling wild fish supplies. At the end of the twentieth century, given the rapid growth of the aquaculture industry, critics began questioning the real social and environmental impacts of aquaculture. The social impacts are generally felt more acutely in poorer countries. For example, people have been displaced from their homes and jobs by aquaculture operations, sometimes by operations that pollute land and water previously used by local residents.

Aquaculture, like any farming activity, produces effects on the environment. Aquaculture uses energy and creates wastes. As aquaculture replaces wild habitat , changes to the ecosystem inevitably occur. Even where aquaculture operations are placed in non-pristine areas, potential exists for exotic (nonnative and genetically altered) aquaculture species to escape and adversely affect native species by competing for food and space, interbreeding and hybridizing native species, and spreading disease. Collecting wild larvae for rearing in aquaculture units can decimate native populations of fish, and can affect biodiversity. Toxic and bioaccumulative compounds can be harmful to people, including fish farmers themselves, and to plants and animals. Excessive discharge of organic wastes causes pollution.

The environmental impacts of effluents depend on the type of aquaculture practiced, and on farm management. Aquaculture can, in local situations, improve the environment or be environmentally benign. If ponds are properly managed, nutrient-rich discharges (soil and water) can be dredged for use in crop production, thereby reducing the need for soil amendments such as inorganic fertilizers.

Fish ponds can increase bird populations, which are pleasing to birdwatchers, but are disdained by fish farmers. While poorly managed fish ponds can serve as breeding grounds for vectors of animal and human disease, well-managed fish ponds can be used to control these vectors. Thus, fish farm management geared at minimizing negative environmental effects can be critical for balancing the farm's impact on the environment, and for its own long-term success.

see also Agriculture and Water; Fisheries, Fresh-Water; Fisheries, Marine; Mariculture; Pollution by Invasive Species.

Hillary S. Egna

Bibliography

Bardach, John, John Ryther, and William O. McLarney. Aquaculture: The Farming and Husbandry of Freshwater and Marine Organisms. New York: Wiley-Interscience, 1972.

Egna, Hillary S., and Claude E. Boyd, eds. Dynamics of Pond Aquaculture. Boca Raton, FL: CRC Press, 1997.

Pillay, T. V. R. Aquaculture and The Environment. New York: Halsted Press, 1992.

Rath, Rajendra Kumar. Freshwater Aquaculture. Jodhpur, India: Scientific Publishers, 1993.

Internet Resources

Review of the State of World Aquaculture. FAO Fisheries Department. FAO Fisheries Circular No. 886 FIRI/C886 (Rev.1), Rome, 1997. <http://www.fao.org/docrep/003/w7499e/w7499e00.htm>.

The State of World Fisheries and Aquaculture 1998. United Nations Food and Agriculture Organization, 2000. <http://www.fao.org/docrep/w9900e/w9900e00.htm>.

U.S. Department of Agriculture. 1998 Census of Aquaculture. <http://www.nass.usda.gov/census/census97/aquaculture/general.htm>.

Aquaculture

Aquaculture is the farming of animals or plants under controlled conditions in aquatic environments. Aquaculture usually refers to growing animals and plants in fresh or brackish water (water that has a salt content between that of freshwater and that of ocean water). Mariculture indicates the farming of animals and plants in ocean waters. (Marine means seawater.) Just as on land, aquaculture and mariculture farmers try to control the environmental factors surrounding their crops in order to make them grow quickly and in good health. Some of the factors that aquaculture and mariculture farmers manipulate are the diet of their animals, the nutrients provided to their plants, the reproductive cycles of both animals and plants, and the chemistry and physical properties of the water where the farms are located. They also try to develop methods to minimize diseases in their crops, to keep their crops safe from predators (animals that hunt them for food), and to reduce the pollution produced by their crops.

The aquaculture and mariculture industry

The combined industry of aquaculture and mariculture represents one of the fastest growing economic areas in the world. According to the United Nations Food and Agricultural Organization (FAO), aquaculture and mariculture have increased by nearly 10% per year since 1970. China has become a world leader in both aquaculture and mariculture. Between 1970 and 2000, China had an annual growth rate of 11.5% in aquaculture and 14% in mariculture. In China, farms produce three times more fish and shellfish for human consumption than fishermen catch.

FAO estimates that aquaculture and mariculture revenues were $56.5 billion in 2000, half of which was generated by China. The crops that generated the largest amounts of revenue were the finfish (catfish, salmon, and talapia), which accounted for about half the world's aquaculture and mariculture production. The other two large crops are mollusks (mostly oysters; mollusks are soft bodied aquatic animals generally having a shell) and plants (mostly kelp). Excluding China, FAO estimates that about one-fifth of the world's fish and shellfish supply comes from aquaculture and mariculture.

Major aquaculture and mariculture crops

A large variety of animals and plants are grown by aquaculture and mariculture. Animals are grown for human consumption, for consumption by other animals, for use in aquaria, for stocking of natural waters and as research animals. Catfish are the most important aquaculture crop in the United States with an estimated 750 million fish grown per year. More than half of these are produced in Mississippi. The next most important fish grown as a crop are the salmon, which are usually raised in pens in bays in the ocean. In 1999, the world mariculture industry grew by more than 1 million tons of salmon. Norway leads the world in salmon farming, followed by Chile. Tilapia is a finfish with mild, tender meat that is becoming an increasingly important mariculture crop.

Shellfish are also grown on farms. The most important crops are oysters, which are grown both for human consumption and for the pearls that they generate. Shrimp, clams, mussels, and abalone are also farmed in marine waters. In freshwaters, the largest shellfish crop is crawfish, followed by shrimp.

Many species of aquatic plants are raised on farms. The major saltwater food crop is kelp, also called wakame in Japan, which is a type of brown algae. This brown algae is also harvested to make agar, a thickening agent used in salad dressings, paint and ink. A red algae, called purple laver or nori, is used in many types of sushi. The most commonly grown freshwater plants for human consumption are watercress and Chinese water chestnuts. Other algae are raised as animal feeds and as mulches and fertilizers (products used by gardeners). Water hyacinth, which efficiently removes excess pollutants from water, is grown for use in wastewater treatment plants.

Catfish Farming

The North American channel catfish is no fragile beauty. Catfish are the hardy, whiskered garbage collectors of sluggish rivers and muddy lakes in the southeastern United States. They can survive in almost any type of fresh or brackish water, and they are scavengers that feed on everything from dead animals to human garbage. In the past, catfish was sometimes considered an unfortunate person's meal. Though plentiful and easily caught, the channel catfish's putrid diet gave its meat the taste of, well, garbage.

In modern day, thanks to aquaculturists in Mississippi, Alabama, Louisiana, and other southern states, mild-tasting catfish is an appealing, inexpensive item on menus at restaurants and grocery store shelves in the United States. When catfish eat feed instead of garbage, their meat tastes good. They are easy to raise in ponds or tanks, and farms have relatively few negative effects on their environment. Unlike other species like salmon or shrimp, they tolerate all kinds of conditions, don't mind living in densely packed ponds, and will eat anything, including inexpensive plant-based feed. Catfish farms do require a lot of water, and they are less welcome in areas where a large-human population is sharing a limited water supply.

Drawbacks to aquaculture

Although aquaculture and mariculture have the potential to make great contributions to the world's food supply, there are some drawbacks to the growth of these industries. In some developing countries, natural habitats are destroyed in order to build pens for crops. For example, shrimp farmers often cut down large areas of trees called mangroves. These trees have the ability to live in salt water. The roots of these trees serve important purposes in the tropical marine ecosystem (community of organisms and their environment). They provide habitats for a

Salmon Farming

Salmon is a delicacy. Like bears, humans find its firm, pink meat tasty and nutritious. The very qualities that make salmon desirable—they have firm muscles from swimming long distances and high protein content from feeding on other fish—make them relatively rare in the wild and expensive to grow on farms. Wild salmon meat has always been an expensive luxury that, like a diamond ring or a fur coat, comes with an environmental cost.

Raising salmon in tanks and pens is a way to provide salmon to restaurants and grocery stores while preserving wild fish. Most species of Atlantic and Pacific salmon are born in cool freshwater streams and lakes, travel down rivers to oceans where they spend their adult years in salt water, and then return to their home streams to lay eggs and die. (Fish that live in both fresh and salt water are called anadromous. Coho, Chinook, Chum, Pink, and Sockeye are all anadromous Pacific salmon.) Human alterations to river systems including dams, water pollution, changes to the amount of silt and mud in the water, and over-fishing have threatened most species of wild salmon.

In modern day, most of the salmon humans eat is raised on farms in cool northern and far southern countries like Norway, Canada, Scotland, Russia, Chile, and Argentina. In the United States, aquaculturists (fish farmers) raise salmon in Washington State and Maine. Aquaculture has made salmon more widely available, but it is still expensive because the fish are difficult to raise in captivity. Salmon farmers accommodate salmon's anadromous life style by spawning and raising young fish in freshwater tanks, and then moving the adult fish to outdoor saltwater pens along coastlines. Salmon are carnivorous (meat-eaters) and it takes about 5 pounds (2.3 kilograms) of fish to produce one pound of salmon meat.

Salmon farming, like most other types of economically-profitable food production, has several drawbacks that concern environmentalists and biologists. Salmon's carnivorous diet threatens other wild species because their feed is made from wild fish. (Raising the feed fish makes farm-raised salmon more expensive than wild salmon.) Environmentalists also worry that salmon pens pollute coastal waters and affect the pristine beauty of northern coastlines. Finally, adults that escape the pens may compete with the wild salmon for resources, spread disease, or mate with wild fish to have babies that cannot survive the rigorous life of wild salmon. (Farm-raised salmon don't have the skills they need to travel thousands of miles [kilometers] in the ocean and then back to their home stream to lay eggs.) Aquaculturists, scientists, and environmentalists are working to find solutions that both protect the wild fish and provide salmon for human consumption.

variety of juvenile fish and invertebrates (animals without a backbone) that hide from predators in their crevasses. They also prevent erosion (wearing away of soil) during floods and storms, by holding soil in place. Finally they use some pollutants, like nitrogen and phosphorus, that are generated by aquatic organisms as they grow.

Pollution is a second problem that aquacultural and maricultural farmers have to confront. Having a large number of animals concentrated in a small area produces much waste. These wastes can stimulate the growth of microorganisms such as phytoplankton and bacteria, which harm animals that live nearby. Some newer technologies involve growing animals in enclosed tanks where water is cleaned and recycled rather than simply released into the environment. Although not yet financially practical, these techniques may represent a cleaner way to farm fish and shellfish in the future.

Finally, the economics of mariculture and aquaculture play a large role in the expansion of these industries. Building and running a facility that grows freshwater or marine organisms is not always profitable. Just as in farming on land, animals and plants that are grown on farms in the water must have traits that allow for domestication. For example, animals that exhibit territoriality or aggressive behaviors are not good candidates for aquaculture or mariculture. Disease can ruin crops, and expensive antibiotics may need to be used to keep animals healthy. Controlling the reproductive rate of farmed animals is extremely important. If animals reproduce too fast, some can become stunted and unable to be sold. If animals reproduce to slowly, costs can overcome profits.

Juli Berwald, Ph.D.

For More Information

Books

Davenport, John, et al. Aquaculture: The Ecological Issues. Malden, MA: Blackwell Publishers, 2003.

Southgate, Paul, and Lucas, John S., eds. Aquaculture: Farming Aquatic Animals. Ames: Iowa State University Press, 2003.

Websites

Harrell, Reginal M. "Finfish Aquaculture Workbook Series." Maryland Sea Grant Extension.http://www.mdsg.umd.edu/Extension/finfish (accessed on August 24, 2004).

"State of the World Fisheries and Aquaculture: 2002." Food and Agricultural Organization of the United Nations.http://www.fao.org/docrep/005/y7300e/y7300e00.htm (accessed on August 24, 2004).

Aquaculture

Aquaculture is the rough equivalent of agriculture on land. Aquaculture is the raising of fish, shellfish, or aquatic plants to supplement the natural supply. Although aquaculture includes the growing of aquatic plants, most people use the term to mean fish and shellfish farming. Fish and shellfish are raised as food under controlled conditions all over the world. The goal of fish and shellfish culture is to increase the yield of useful products, including increased food production.

While most aquacultural production is in food items such as fish, mollusks , and crustaceans , some marine algae, kelp, and other aquatic plants are raised commercially. Cultured pearls are created by placing small bits of material in the shells of young oysters. Various types of floating algae and phytoplankton are also grown, primarily as food for animals.

Aquatic animal husbandry includes all of the activities terrestrial farmers and ranchers have used, such as selective breeding, care of the young, feeding, sanitation, environmental modifications, and harvesting. Species having characteristics that make them suitable and practical for culturing are selected for extensive cultivation. This includes considerations of consumer choice. Aquaculture is relatively expensive, so most aquacultural products are luxury items such as trout, oysters, and shrimp. Some less expensive fish species, such as carp and tilapia, are successfully cultured in China, India, and southeast Asian countries.

History of Aquaculture

Aquaculture has been practiced for thousands of years. Chinese in the fifth century C. E. practiced aquaculture, and temple friezes (ornamented bands on a building) dating from the Middle Kingdom of Egypt (2052-1786 B. C. E. ) depict what appear to have been intensive fish farming. The ancient Romans are known to have cultivated oysters.

Commercial Importance

As suitable arable land diminishes and the world's population increases, aquaculture is expected to become increasingly important. Aquaculture is an environmentally friendly source of high-quality animal protein. Many countries with limited arable land, such as Japan, are actively developing an aquaculture industry.

Problems of Aquaculture

Aquacultural practices are not as efficient as they could be. Lack of capitalization in developing countries, inefficient and outdated techniques, and poor marketing all contribute to the lack of commercial success in aquaculture. Another factor limiting production is the lack of suitable domesticated species. Only a few aquatic animals are used, and much of the life cycle of these animals is not controlled. Research into new species, development of commercially viable hybrids , and new techniques of breeding should improve the efficiency of commercial aquaculture. Continued research and the dissemination of new skills and techniques holds promise for substantially increased aquacultural production, perhaps exceeding 30 million metric tons (33 million short tons) per year.

Selection of Suitable Species

In order to be aquaculturally useful, species must be able to reproduce in captivity, have robust eggs and larvae, feed on inexpensive food, and grow quickly to harvestable size. For example, trout and carp have large, hardy eggs; mullet fry are easily collected; and young oysters are easily collected and grown. So these were the species of choice for aquaculture. The feeding habits of species also limit suitability. Wide-ranging plankton feeders, such as herring, are not suitable. Sessile animals, such as oysters and mussels, which filter the water for their food, can be cultured extensively but still must be supplied with a rich food supply if they are to grow rapidly.

Selective Breeding

Aquaculturists, like their terrestrial counterparts, selectively breed for desirable traits in captive organisms. Since the traits that enhance success in a wild population are often inconsistent with a successful captive population, these traits must be eliminated through breeding. Desirable characteristics include fast growth and a body shape that provides more edible tissue. Since captive populations are usually held at a higher density than wild populations, disease is a problem. So resistance to disease is desirable. Since aquatic animals usually produce many offspring per generation, selective breeding is somewhat easier than with terrestrial animals.

One desirable characteristic of captive populations is an accelerated onset of sexual maturity. This event is triggered in the wild by a combination of factors, including water temperature, length of daylight hours, and salinity. These factors in turn act on the animal's pituitary gland, which controls the output of sexual hormones. Attempts to control environmental factors to accelerate spawning have been largely unsuccessful, except in the cases of oysters and shrimp. A more generally successful method involves the injection of pituitary hormones. This is expensive and labor intensive so alternatives are being sought.

Evolving Technologies

Large-scale fish culture projects, if properly managed, have the potential to produce thousands of tons of fish. Community ponds and reservoirs created by the damming of tropical rivers are often designed to include largescale fish farming. When a new reservoir is created, nutrients from the soil trigger the growth of abundant algae and aquatic plants. So herbivorous fish must be included in the plans. These fish can provide the first harvested "crops."

Fish "ranching" is also widely practiced. For example, salmon are raised in hatcheries then released into wild streams. This allows the establishment of new salmon runs, the reintroduction of salmon into previously used streams, and the replenishment of depleted stocks. This form of aquaculture also helps alleviate losses due to human-induced environmental degradation.

Hybridization is another technique coming into use in aquaculture. Crossing one trout with another trout having seagoing tendencies enables breeders to send fish to new oceanic pastures and then to harvest them when they return to freshwater to spawn. Promising crossbreeding experiments with tilapia have also resulted in species exhibiting hybrid vigor.

Both coal-fired and nuclear power plants use water for cooling. This water is generally discharged into a reservoir of evenly warmed water. This water has significant potential to be used in aquacultural programs. Many aquatic animals grow more rapidly in somewhat warmer water. Other species, such as carp and catfish, prefer warmer water. Many of the farmraised catfish available in supermarkets are grown in ponds warmed by water from power plants.

Pelagic (open ocean) fish have not been raised in captivity with any great success. They are desirable species because they grow fast. But they require huge quantities of food fish or other pelagic organisms, which are also hard to raise in captivity. As research continues, it is likely that new aquacultural techniques will be developed that will permit the farming of many new species such as spiny lobsters, crayfish, octopus, and others not presently husbanded. Improved techniques will increase the yield of existing aquacultural species. As demand continues to increase for world food supplies, aquaculture promises to grow into a thriving and productive industry.

see also Farming.

Elliot Richmond

Bibliography

Curtis, Helena, and N. Sue Barnes. Biology, 5th ed. New York: Worth Publishing, 1989.

Lovell, Tom. Nutrition and Feeding of Fish. New York: Van Nostrand Reinhold, 1988.

Miller, G. Tyler, Jr. Living in the Environment, 6th ed. Belmont, CA: Wadsworth, 1990.

Purves, William K., and Gordon H. Orians. Life: The Science of Biology. Sunderland, MA: Sinauer, 1987.