Pens for aquaculture are large enclosures, constructed of nylon, plastic, or steel mesh and attached to a floating raft positioned in a reservoir. Pen culture permits interaction with the immediate environment, but prevents the entry of undesirable fish and other animals that might harm the fish crop.

Fish are more easily harvested from pens than from a large reservoir and circulation of the reservoir water through the pen provides good water quality including adequate oxygen on a continuous basis. When pen culture relies solely on natural foods (extensive – no feed inputs), it is a highly sustainable method of fish production. Advantages include use of existing water bodies, comparatively low capital requirements and use of simple technology.

Extensive pen culture is popular with farmers, out-reach workers and development programs. This practice not only  produces  high quality protein cheaply but may also serve to “clean” highly eutrophic (fertile) waters when  planktivorous (feeding on small minute plants and/or animals) fish species are cultured. This is accomplished through the food chain as the plankton assimilate nutrients, are consumed by the fish and farmers remove the fish from the reservoir at harvest time. 

China has used extensive pen culture since the 1950’s for production of filter feeding bighead and silver carp. 

Paddlefish were introduced as an alternative species in the pens beginning in 2009 and market acceptance has been excellent. The pens are about 6 m x 6m x 3.7 m (20 ft x 20 ft by 12ft) and constructed of 64 mm (1/4 inch) polyethylene mesh. Thirty cm (12 inch) paddlefish are stocked at 200 fish per pen. Farmers suspend energy saver light bulbs over the pens to draw zooplankton into the cage at night for the fish to consume. The fish are harvested after about 12 months when they reach 0.7-0.9 kg (1.5-2 lbs). Chinese farmers are receiving the equivalent of $8/0.45 kg (one lb) from high-end restaurants that sell the fish as a delicacy with prices ranging from $40 to $100/plate. Though the extensive pen culture method is successfully practiced in large reservoirs in many countries, this method is restricted in the United States to privately owned ponds and lakes and is not permitted in public reservoirs. 

Extensive Pen Culture
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