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.