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 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 the 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.

Shellfish are also grown on farms. The 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 commonly grown freshwater plants for human consumption 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 wastewater 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.

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.