Agricultural Fish Farming

Fish farming is practiced all over the world. National Geographic reports that about half of the fish we consume now comes from farms. Large commercial fish farms raise a wide variety of aquatic life, from catfish in ponds to large cages or nets in oceans and seas. Specialty fish farms frequently use tanks to grow large numbers of fish in a concentrated area.

Types

In the United States, most agricultural fish farms consist of specially constructed ponds. In the Far East, fish are grown in flooded rice paddies. In arid countries, irrigation systems do double duty as fish farms. In many countries, gates are placed in streams to contain fish in the headwaters for later harvesting.

Construction

Agricultural fish farming ponds are constructed to facilitate the particular species being raised. Some ponds have shallow areas for growing vegetation and deeper areas where the fish can escape from the sun and warmer surface water. Some ponds are like large bowls, so the fish may be "herded" and netted by hand at the end of the growing season.

Some aquatic species, such as freshwater prawns, cannot be netted; those ponds must be drained for harvesting, so they are constructed with a sloping bottom. A trough may be dug out at the deepest end. At harvest time, the pond is drained and all of the animals will move to the deepest part where they can be netted and removed.

Care and Feeding

Regardless of the type of fish farm, the enclosed animals are dependent upon the fish farmer for most of their care. The farmer must provide adequate nutrition, protect the fish from disease and predators, and monitor water quality. Each species of fish has a different diet. Some will require daily feeding of commercial fish food, some require vegetation to balance their diets, and some will survive on the waste products of other aquatic life.

Water Quality

Managing water quality is the most critical area of agricultural fish farming. Oxygen levels must be maintained within a specific range for each species. Various methods of oxygenating water are used, including bubbler systems, paddle wheels, concentrated oxygen and even oxygen tablets. Chemical levels must also be controlled. Excessive phosphorous and nitrogen, which may be introduced into the pond from agricultural runoff, are especially dangerous to fish farms.

Algae Control

Phosphorous and nitrogen, along with normal waste from fish and vegetation, encourage the growth of algae. If not closely monitored, algae may reproduce too rapidly for the farmer to control. When algae take over a pond, other plants and animals begin to die, bacteria multiply to consume the waste, and the excessive bacteria uses up the available oxygen, quickly killing everything else in the pond.

References

• Aquaculture Basics
• Fish Kills from Harmful Algae
• World Fisheries and Aquaculture

Resources

• National Geographic - Future Fish Farms
• The Promise and Perils of Fish Farming