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.
Japanese farmers tend commercial oyster beds.
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 aquacul-ture 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 nex most important fish grown as a crop are th< salmon, which are usually raised in pens ii bays in the ocean. In 1999, the world mari culture industry grew by more than 1 million tons of salmon. Norway leads the world in salmon farming, followed by Chile. Tilapia i; a finfish with mild, tender meat that i; becoming an increasingly important mari culture crop.
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.
Shellfish are also grown on farms. Th< most important crops are oysters, which ar grown both for human consumption and fo the pearls that they generate. Shrimp, clams mussels, and abalone are also farmed in marine waters. In freshwaters, the larges shellfish crop is crawfish, followed b shrimp.
Many species of aquatic plants are raisec on farms. The major saltwater food crop i; kelp, also called wakame in Japan, which is ; type of brown algae. This brown algae is also harvested to make agar, a thickening agen used in salad dressings, paint and ink. A red algae, called purple laver or nori, is used in many types of sushi. The most commonl grown freshwater plants for human con sumption are watercress and Chinese wate chestnuts. Other algae are raised as anima feeds and as mulches and fertilizers (prod ucts used by gardeners). Water hyacinth which efficiently removes excess pollutant from water, is grown for use in wastewate treatment plants.
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 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.
Salmon Farming
A fish farm worker nets salmon in British Columbia, Canada.
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.
Algae and fish are grown in cages by the sea in this Israeli aquaculture center.
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.
WORDS TO KNOW
Anadromous: Fish that are born in fresh water and then move to marine water as adults.
Brackish: Water with a salinity between that of freshwater and ocean water.
Invertebrate: Animals without a backbone.
Mariculture: Farming animals and plants under controlled conditions in marine waters.
