Blue Revolution (Fish Farming)

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Blue revolution (fish farming)

The blue revolution has been brought about in part by a trend towards more healthy eating which has increased the consumption of fish. Additionally, the supply of wild fish is declining, and some species , such as cod, striped sea bass, salmon , haddock, and flounder, have already been overfished. Aquaculture , or fish farming, appears to be a solution to the problems created by the law of supply and demand. Farm-raised fish currently account for about 15% of the market. There are 93 species of fin fish, seven species of shrimp, and six species of crawfish, along with numerous species of clams, oysters and shellfish that are currently being farm raised worldwide.

There are five central components to all fish farming operations: fish, water supply, nutrition, management and a contained method. Ideally, every aspect of the fishes' environment is scientifically controlled by the farmer. The quality of the water should be constantly monitored and adjusted for pH and numerous other factors, including oxygen content. Adequate water circulation is also necessary to insure that waste matter does not accumulate in the cages, for this can lead to outbreaks of disease. The fish are fed formulated diets that contain only enough protein for optimal growth. They are fed regulated amounts that vary according to stage of development, water temperature, and the availability of naturally occurring food in their habitat .

Herbicides are used on a regular basis to control any unwanted aquatic vegetation and to prevent fouling of cages. Vaccines are routinely given to the fish to prevent disease, although their effectiveness against most pathogens has yet to be determined. Antibiotics are routinely placed in the food that is fed to farm raised fish, a practice which many have questioned. When given over a prolonged period of time, antibiotics can result in higher incidences of disease because bacterial strains develop resistance to them.

Fish that are raised on farms mature in rearing units that are frequently located on shore. These on shore units are typically ponds, large circular tanks or concrete enclosures. Many types of freshwater fin fish are raised in pond systems. Ponds that are easy to harvest, drain and refill are the most economical. Walleye, perch and northern pike are a few of the cool-water species that are raised in pond cultures. Warm-water species such as catfish, carp, and tilapia are also common. A few cold water species, especially trout and salmon, can also be raised in pond systems. Most pond systems are monoculture in nature , so only one type of fish is raised in each pond.

Silos, raceways, and circular pools are commonly used in fish farming. These are popular because they require a small land base in comparison with most other systems. Trout and salmonoid species are frequently raised in raceways, which are rectangular enclosures usually made of cement, fiberglass or metal, and positioned in a series so that water flows from one into the next. Circular pools are shallow with a center drain. They are easy to clean and maintain, since the growth of aquatic vegetation is usually minimal. Silos are very deep, circular tanks that are similar to silos used for grain storage on traditional farms.

All on shore fish farming operations use large quantities of water, and their operations are either open or closed systems. In open systems the water is used only once, flowing into a pool or through a series of pools before being discharged into a drainage ditch, creek, or river. Open systems are used whenever possible because they are relatively inexpensive. In most cases, farmers are not required to treat the water before it is discharged, which poses an environmental hazard because the organic fish wastes, the residues of medications, and the herbicides used in the operation enter the water supply unchecked.

Closed systems are not popular among fish farmers because they are very expensive to build, maintain and operate. In a closed system used water is treated and then reused in the farming operation. The treatment process can include disinfection, removal of organic wastes that have dissolved in the water, and reaeration. The closed system is more environmentally sound than the open systems.

Coastal lakes and estuaries are the most frequently used off-shore sites for rearing units, but it is becoming more common to see units located at sea. There are four basic types of cages used for off-shore fish-farming operations. They are fixed, floating, submersible, and submerged. Fixed cages are made of net or webbing material and supported by posts that are anchored in the river bottom. Floating cages, also known as net pens, are the most common type of cage used. Developed in Norway, they are made of net or rigid mesh and are supported by a buoyant collar. Submersible cages have a frame which enables them to hold their shape made of net or rigid mesh and are supported by a buoyant collar. Submerged cages are usually made of wood and anchored in place.

One major concern about off-shore nets and pens is that they tend to attract marine birds and mammals, which attempt to get at the fish with often fatal results. Fish farmers currently use wire barriers and electrical devices to discourage predators and these devices have killed sea lions . A typical four-acre salmon farm holds 75,000 fish, and the amount of organic waste produced is equal to that of a town with 20,000 people. Waste matter then settles on the ocean floor, where it disrupts the normal ecosystem . Accumulated wastes kill clams, oysters and other shellfish, and also causes a proliferation of algae, fungi , and parasites , as well as plankton bloom. Plankton bloom is dangerous to sea life and to humans. In order to control the algae and plankton farmers treat the fish and the water with numerous chemicals such as copper sulfate and formalin. These chemicals do not act exclusively on algae, killing many other beneficial forms of aquatic life and disrupting the ecological balance. According to the Sierra Club Legal Defense Fund, the pens qualify as point sources of pollution and should fall under the Clean Water Act . At this point in time, however, the pens do not come under the jurisdiction of the act.

Many fish on farms are raised from eggs imported from other areas. Farm-raised fish can and do escape from their pens, causing havoc with local ecosystems. The interbreeding of imported fish with indigenous species can alter the genetic traits that allow the indigenous species to survive in that particular location. Farm-raised stock that escapes and reproduces may also compete with native species, resulting in the decline of wild fish in that particular area. Off the coast of Norway for example, the offspring of escaped farm-raised salmon outnumber the indigenous species.

There are many questions about health and nutrition that may affect consumers of farm-raised fish. Fish farmers frequently use large quantities of medications to keep the fish healthy and there are concerns over the effects that these medications have on human health. Possible side effects of eating farm-raised fish on a regular basis include allergic reactions, increased incidence of infections by resistant bacterial strains, and suppressed immune system response. If eaten by pregnant women there is evidence of fetal damage, discoloration of infants teeth, and abnormal bone growth. Omega-3 fatty acids are a beneficial part of our diet and they are present in the flesh of wild salmon and in some other fish, but not in their farm-raised counterparts. Recent studies have found that farm-raised salmon and catfish contained twice the amount of fat found in wild species. Other comparative nutritional studies are currently underway.

Fish farming is a relatively new industry that shows a lot of potential, but there are many environmental and health questions that need to be addressed. Monitoring of the industry is virtually non-existent. In the United States, the Joint Subcommittee on Aquaculture (JSA) has made recommendations for additional studies of the industry including the environmental impact of fish farming. JSA has pointed out the need for extensive research into the life cycle of parasites and diseases that plague fish. They have recommended drug and chemical testing as well as registration procedures. In the 1983 report issued by JSA every aspect of the farming operation was cited as needing additional studies.

See also Agricultural pollution; Algal bloom; Aquatic chemistry; Aquatic weed control; Commercial fishing; Feedlot runoff; Marine pollution; Water quality standards

[Debra Glidden ]



Beveridge, M. Cage Aquaculture. Farham, England: Fishing News Books, 1987.

Brown, E. E. World Fish Farming: Cultivation and Economics. Westport, CT: Avi Publishing Company, 1983.


Fischetti, M. "A Feast of Gene-Splicing Down on the Fish Farm." Science 253 (2 August 1991): 512-3.