World Aquaculture Magazine - June 2020

20 JUNE 2020 • WORLD AQUACULTURE • WWW.WA S.ORG percent of shrimp produced in the country (MARD 2019). Shrimp culture is diverse, with systems such as integrated mangrove- shrimp, improved-extensive, rotational rice-shrimp, intensive and super-intensive shrimp farming systems. Large areas of integrated mangrove-shrimp farming systems (50,000 ha) and improved-extensive shrimp farming systems (300,000 ha) in the Mekong Delta are traditional and characterized by low investment and simple management, with a productivity of 300-400 kg/ha per year, and are considered to be environmentally friendly farming systems. Under climate change, important solutions have been introduced and practiced widely such as maintaining high water levels of about 30-40 cm on the pond central platform, nursing shrimp postlarvae for larger and higher- quality seed, and diversifying the species cultured with shrimp, mud crabs, brackishwater fish and seaweeds. Production from integrated mangrove-shrimp farming systems is being certified as organic. Rotational rice-shrimp farming systems (Fig. 1) are specific to the Mekong Delta, with over 170,000 ha of area. Under climate change and saltwater intrusion, this is considered a strategic system for agri-aquaculture production and is planned for expansion up to 250,000 ha with production of 125,000-150,000 t by 2030 (AMDI 2015). During the dry season, with brackish water (3-15 g/L salinity), shrimp are cultured with one crop of tiger shrimp (2-7/m 2 ), or two crops of whiteleg shrimp (5-20/m 2 ), or one crop of tiger shrimp and one crop of whiteleg shrimp. Shrimp are fed casually at low stocking densities or fed with pelleted feed daily at high stocking densities. During the rainy season (0-3 g/L salinity), traditional and salt-tolerant rice is cultivated and integrated with giant freshwater prawn (1-2/m 2 ). Rice use waste nutrients from shrimp culture for growth without or with only limited fertilizer application. Shrimp production is around 0.3-1.5 t/ha per crop (AMDI 2015, Huong 2016, Mai 2016). The system is considered to be environmentally friendly, moderate in capital investment and technical management, and especially adaptive to climate change and saltwater intrusion for food security. Recently, nursing shrimp postlarvae in plastic-lined earthen tanks with biofloc technology for two-phase shrimp culture has become very important and widely applied to improve shrimp seed quality and shorten the grow-out period as an adaptation to climate change and uncertain seasonal intrusion of saltwater (Hai et al. 2020). Rotational rice-shrimp farming systems are now targeted toward certification of organic production, for both rice and shrimp with large projects being implemented (MARD 2019). In addition to the traditional and integrated systems mentioned above, the shrimp culture industry is now undergoing intensification and modernization in over 100,000 ha, with production of 5-10 t/ha per crop for intensive culture and 20- 40 t/ha per crop for super-intensive culture of whiteleg shrimp. Under climate change conditions, environmental management and market requirements, big changes in technological and legal management are being implemented. Unlike conventional one- phase intensive culture systems for tiger shrimp in large earthen ponds (0.3-0.5 ha), which is very sensitive to climate change (Mai 2017), intensive and super-intensive shrimp farming is now dominated mostly by whiteleg shrimp, farmed in smaller (500- 1000 m 2 ) HDPE-lined earthen ponds or round tanks, placed in an indoor greenhouse or outdoor nethouse (Figs. 2 and 3). Two-phase shrimp culture is mostly applied which enables multiple crops annually, shortening the culture period for grow-out, enhancing environment control and reducing the risk of disease problems. Biofloc or “semi-biofloc” is applied and enhanced mostly with sugar molasses. In many cases, discharged water is treated and reused through large storage ponds with stocked fish. Super- intensive shrimp culture is increasingly practiced by companies or entrepreneurs with good technical skill and high capital. However, household-scale farmers also apply the approach. Results of two-phase super-intensive shrimp culture in tanks under a nethouse at a commercial company in Bac Lieu province was studied. For the first phase, whiteleg shrimp post-larvae are nursed in 100-m 3 tanks at 2500/m 3 for 16 days, with survival of 82-91 percent. Juveniles are then transferred to 500-m 3 tanks for the second phase of grow-out for 74 days, reaching very high production of 5-6 kg/m 3 (3,009 ± 346 kg per 500-m 3 tank). Advanced recirculating systems for super-intensive shrimp culture in tanks are currently under development at Can Tho University, indicating potential for further application in the region, even at large or small scale, in rural or urban areas, to deal with climate change and to meet the need for biosecurity, FIGURE 2. Intensive shrimp culture in lined ponds in a greenhouse. FIGURE 3. Super-intensive shrimp culture in round tanks in a net-house.