The practice of fish farming is called aquaculture and it's a fast-growing segment of the U.S. economy. Aquaculture produces more protein per acre than cattle, chicken or other livestock. Due to rising international demand, farmed fish are expected to supply 41 percent of the world's supply by 2020. Commercial fish farmers use natural water formations, such as ponds and lakes as well as artificial formations like raceways and aquariums to provide their fish with an environment to grow.
Open Water Source
To farm fish in an open body of water, such as a lake or ocean, farmers can erect nets and cages that float in the water, often called "purse-seines." These cages aren't sealed, however, so it's possible that fish can escape or breed with nearby species; the cages can also capture endangered fish or unwanted species that are thrown out when the net is brought to the surface. These nets are used mainly to farm and harvest free-swimming fish, including bluefin tuna that don't thrive in more contained environment.
Closed Water Source
Most freshwater fish can be raised easily in an enclosed body of water, such as a natural pond or man-made tank. Raceways are a third type of environment in which water is diverted from a natural source, such as a river and flowed through man-made channels populated with farmed fish.
Fish Species Selection
Fish farmers can raise trout, tilapia, salmon, tuna, catfish, bass, sturgeon, carp, Nile perch, shrimp. The type of fish raised will depend on the farmer's available water and growing conditions, such as temperature. Catfish and trout, for example, can both grow easily in manufactured ponds. Catfish, however, require a water temperature of between 80 and 90 degrees F that would kill a trout.
Fish Farming Supplies
Large-scale fish farmers need a suitable amount of land, source of clean water, eggs and fish food. Although fish can be farmed at densities of up to 2,000 lbs. an acre, that land must be populated with ponds or raceways, pipes, tanks, aerators and oxygen meters---all carefully tested and monitored to maintain water purity, water oxygen content and overall fish health. Smaller-scale farms can be created with a single aquarium or several backyard ponds, although the same monitoring equipment is needed to produce optimal water quality, temperature and oxygen content.
Management: Water Quality
Water quality is affected by its pH and the effects of fish waste. Farmers must keep their water at a pH between 6.5 and 7; they do this by adding lime to reduce acidity and adding gypsum to reduce alkalinity. Filtering water through charcoal can remove toxic chemicals, such as chlorine. Installing a water filter encourages the growth of helpful bacteria that can digest fish waste and keep potentially harmful nitrogen levels in check.
Oxygen Content
All water contains oxygen---this is what keeps the fish alive and breathing. Fish farmers control the amount of oxygen in their water with a combination of natural and artificial methods. Natural methods involve placing oxygen-producing plants and algae into the fish habitat. Through the process of photosynthesis, the plants release oxygen into the water. If that isn't sufficient, farmers can place aerators in the fish habitat that pump air through the water, increasing water flow and oxygenation.
References
- Back to Basics: A Complete Guide to Traditional Skills by Abigail R. Gehring
- International Food Policy Research Institute: Outlook for Fish to 2020
- Monterey Bay Aquarium Seafood Watch: Aquaculture Fact Cards
- Monterey Bay Aquarium Seafood Watch: Bluefin Tuna
- Virginia Cooperative Extension: Should You Attempt Fish Farming?
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