Raising prawns is a form of aquaculture where freshwater or saltwater prawn or shrimp are kept in controlled environments. A low-intensive method was practiced in southeast Asia until highly intensive models took hold in the boom years of the industry in the 1980′s and 90′s. This has had far-reaching impacts that were largely unanticipated, where shrimp farming took off and was unregulated. Due to these problems, which included massive disease outbreaks that decimated stocks and environmental degradation, the practice has been regulated and sustainable methods have been introduced.
Sustainable methods include the Tambak system, used in Indonesia, where rice paddies are used to capture shrimp. Dikes that protect paddies from tidal surges are breached. When the tides fill in the paddies, prawns and small larval fish are captured to raise and the paddies are converted back to rice cultivation.
In Hong Kong, the Gei Wai method use the natural aquatic nursery that is a mangrove forest. Large channels are excavated and used as breeding pools for, shrimp, mollusks and fish. These are the Gai Wais. When tidal surges come in, they replenish the nutrition in the gei wai, flowing through a sluice gate where water can enter in, but fish can’t escape. Both the gei wai and Tambak have been practiced for hundreds of years to feed local populations, but they can’t reach levels necessary to sustain international demand for shrimp. In fact, only one gei wai remains in Hong Kong, as an historical preservation site.
A “closed” intensive shrimp farming system is gaining traction to provide enough shrimp for consumer demand, which is more closely in line with sustainable aquaculture practices. Large, indoor tanks are set up in facilities where wastewater is treated and recirculated, having a less-impactful relationship that “open” coastal shrimp farms have had on the environment. Experimental facilities such as these have been set up in Texas and Virginia.
Integrated, semi-open aquaculture systems provide feed to shellfish, finfish and seaweed: when the effluent water from the shrimp stocks is changed, it is fed to these species, making the negative outputs of one system become the positive inputs of the other.
The cost of entry into these new, experimental systems is rather pricey and cannot be replicated economically on a home scale. The advantage closed shrimp aquaculture has, however, aside from its lessened ecological footprint is that variable are under the control of the farmer and not natural cycles, which can play havoc for open systems. Closed systems managers can even stagger their harvests, culling as many shrimp as orders demand.