A FRESHWATER PRAWN FARM

A freshwater prawn farm is an aquaculture business designed to raise and produce freshwater prawn or shrimp1 for human consumption. Freshwater prawn farming shares many characteristics with, and many of the same problems as, marine shrimp farming. Unique problems are introduced by the developmental life cycle of the main species (the giant river prawn, Macrobrachium rosenbergii).

The global annual production of freshwater prawns (excluding crayfish and crabs) in 2003 was about 280,000 tons, of which China produced some 180,000 tons, followed by India and Thailand with some 35,000 tons each. Additionally, China produced about 370,000 tons of Chinese river crab (Eriocheir sinensis)

Technology :- Giant River Prawns have been farmed using traditional methods in south-east Asia for a long time. First experiments with artificial breeding cultures of M. rosenbergii were done in the early 1960s in Malaysia, where it was discovered that the larvae needed brackish water for survival. Industrial-scale rearing processes were perfected in the early 1970s in Hawaii, and spread then first to Taiwan and Thailand and then to other countries.

The technologies used in freshwater prawn farming are basically the same as in marine shrimp farming. hatcheries produce postlarvae, which then are grown and acclimated in nurseries before being transferred into growout ponds, where the prawns are then fed and grown until they reach marketable size. Harvesting is done by either draining the pond and collecting the animals ("batch" harvesting) or by fishing the prawns out of the pond using nets (continuous operation).

Due to the aggressive nature of M. rosenbergii and the hierarchy between males, stocking densities are much lower than in penaeid shrimp farms. Intensive farming is not possible due to the increased level of cannibalism, so all farms are either stocked semi-intensively (4 to 20 postlarvae per square metre) or, in extensive farms, at even lower densities (1 to 4/m²). The management of the growout ponds must take into account the growth characteristics of M. rosenbergii: the presence of blue-claw males inhibits the growth of small males, and delays the metamorphosis of OC males into blue-claws. Some farms fish off the largest prawns from the pond using seines to ensure a healthy composition of the pond's population, designed to optimize the yield, even if they employ batch harvesting. The heterogeneous individual growth of M. rosenbergii makes growth control necessary even if a pond is stocked newly, starting from scratch: some animals will grow faster than others and become dominant BCs, shunting the growth of other individuals.

The FAO considers the ecological impact of freshwater prawn farming to be less severe than in shrimp farming. The prawns are cultured at much lower densities, meaning less concentrated waste products and a lesser danger of the ponds becoming breeding places for diseases. The growout ponds do not salinate agricultural land, as do those of inland marine shrimp farms. Freshwater prawn farms do not endanger mangroves, and are better amenable to small-scale businesses run by a family. However, like marine farmed shrimp, M. rosenbergii is also susceptible to a variety of viral or bacterial diseases, including the White Tail Disease , also called "White Muscle Disease".