WWW.WAS.ORG • WORLD AQUACULTURE • DECEMBER 2014 49 vannamei, was cultured at a large scale in Guangdong Province, with the farming area expanding quickly at that time. Although thought of as a marine penaeid shrimp, L. vannamei can also be cultured in fresh water, so it soon outgrew M. rosenbergii and became the most popular culture species with the farmers of Guangdong Province. Freshwater prawn farming had another period of rapid development from 2004 to 2009. The production of cultured freshwater prawn increased rapidly with implementation of more intensive farming and improved culture techniques. The production area increased quickly during this period, especially near Gaoyou city, Jiangsu Province. In 2009, production reached 144,467 t, 63 percent of global farmed giant freshwater prawn production (Fig. 1). Currently the majority of giant freshwater prawn production is concentrated in the Yangtze River Delta and Pearl River Delta. Current Status and Production Practices The spectacular increase in giant freshwater prawn production is partly the result of the increase in culture area and rapid development of intensive culture. China’s biggest giant freshwater prawn culturing and producing region is near Gaoyou City, Jiangsu Province. There, in 2009, the farming area reached 10,000 ha with a production of 53,300 t, and farming profit increased to US$ 6250/ha. The profitability stimulated more farmers to begin freshwater prawn culture. As a tropical species, M. rosenbergii is sensitive to low temperature. The appropriate water temperature range is 22-32 C and the temperature range for optimal growth is 29-31 C (Chen et al. 1981, New 1990). When post-larvae are stocked, the water temperature should be above 20 C. Post-larvae of M. rosenbergii cultured in outdoor ponds in the Yangtze River Delta region can only be stocked at the end of May because of temperature restrictions. Marketable prawns are harvested in October when water temperature falls below 20 C. Therefore, only a single crop of freshwater prawn can be cultured in a year in China because production is restricted to the 4-5 months of warm weather. Continuous innovations in aquaculture technology and many new efficient farming modes have been developed by the joint efforts of researchers and farmers. With the great progress in farming technology, the stocking density of M. rosenbergii also has increased. In general, increased stocking density results in an increase in production and higher revenues, enhancing economic performance substantially. At present, local farmers in the Yangtze River Delta region use ponds covered with plastic greenhouses to increase water temperature, allowing stocking of seed in spring (generally in early March). This system is combined with selective harvest and multistage rotational stocking systems to allow increased production. When prawns reach market size, they are selectively seined and smaller animals are returned to ponds. This method allowed sufficient time for grow-out of smaller prawns remaining in ponds. Through stocking ponds in batches, prawns can be provided continuously to the market. Prawn famers can get higher profits by selling live animals in the market, inasmuch as the Chinese prefer to cook fresh aquatic products (Yang et al. 2012). These measures improve yield and extend the marketing time of fresh aquatic products from two months to more than four months. The influences of improved unit yield and earlier marketing of commodity prawns on enhanced economic performance are substantial. Most prawn farmers stock seed into plastic-covered greenhouses during March and April every year. The stocking density is generally 100-150 PL/m2 during the culture period. The first batch of PLs, grown to juveniles, is acclimatized in heated greenhouses before stocking in outdoor grow-out ponds. After about one month, the first batch of PLs grows to 3-cm juveniles and the second batch of PLs is moved into nursery greenhouses. When the outdoor water temperature exceeds 20 C, plastic-covered greenhouses are removed and all juveniles are stocked into outdoor ponds. If desired, a third batch of PLs is stocked directly into outdoor ponds as supplementary seed. Therefore, ponds are stocked with large, medium and small animals in outdoor grow-out ponds. Harvest of marketable prawns must be done periodically (every 10 days) to provide sufficient space for smaller animals remaining in ponds to grow rapidly. In general, ponds are first seined in late June. Larger, commercial-size prawns are selectively harvested and smaller ones returned to ponds. Selective harvest of larger animals can be effective for increasing total yield. Ponds are drained and all animals sold before late October. Average production is 5,250 kg/ha by this system. Greater production is over 7,500 kg/ha and the highest can reach 9,000 kg/ha. (CONTINUED ON PAGE 50) FIGURE 2. An early maturing female Macrobrachium rosenbergii. The spectacular increase in giant freshwater prawn production is partly the result of the increase in culture area and rapid development of intensive culture. China’s biggest giant freshwater prawn culturing and producing region is near Gaoyou City, Jiangsu Province. There, in 2009, the farming area reached 10,000 ha with a production of 53,300 t, and farming profit increased to US$ 6250/ha. The profitability stimulated more farmers to begin freshwater prawn culture.
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