Clam farming is an aquaculture enterprise in which clams are raised and harvested for food under semi-controlled conditions. These farms exist in many areas of the world and usually are found in areas where there are shallow bays and estuaries. Many clam species are farmed, often in areas where they occur naturally. Clam farming can be a simple operation of nurturing wild clam habitats and harvesting them or a comprehensive process with clam hatcheries and nurseries.
All clams are bivalve mollusks but exhibit a great deal of diversity. They have been harvested for food for thousands of years, and North American native peoples from the Pacific northwest have legends of the first men rising from clamshells to claim the land. Since earliest recorded history, men have harvested clams all over the world. Clam farming, however, is a relatively modern activity. In its earliest form, clam farming consisted of small farms that were maintained by families or individuals who would often fence off productive clam beds to keep out predators.
In the first half of the 20th century, clam farmers began breeding clams to produce new varieties to raise in their farms. These techniques evolved over the following decades into the process used by many commercial clam farmers today. Male and female clams are induced to spawn in tubs by an alternating flow of warm and cool seawater which simulate spring tides. The larvae that hatch from the newly fertilized eggs are kept in special tanks for up to two weeks and fed a diet of microscopic algae.
As the clam larvae grow, they lose the ability to swim and settle to the bottom of the tanks. They are collected and moved to other tanks where they grow to a size of approximately a 0.25 to a 0.5 inches (8-15 mm). Once they reach this size, these "seed" clams are ready for "planting." They are planted into the ocean bottom in shallow coastal waters, protected by fences, nets. and mesh screens to keep out predators.
For the next two to three years, the clams are allowed to grow until they reach market size. During this period, the clam farmer tends his clam beds in much the same way a terrestrial farmer tends his fields. The fences and protective mesh must be monitored for damage and debris. New beds are "planted" in a rotation so that clams are available for harvest each year.
Clam farming around the world varies somewhat according to region and species, but the basic idea remains the same. Some clam species are housed in cages for protection because some species live on the bottom itself rather than under the ocean bottom. In Micronesia, giant clams, some reaching as large as 5 feet (1.4 m) in length are farmed in shallow island lagoons and are protected by cages of coated wire or bamboo.