36 MARCH 2015 • WORLD AQUACULTURE • WWW.WAS.ORG white shrimp due to its advantages of short culture duration, high production, low risks of diseases and loss. However, Pacific white shrimp culture needs greater investment of technology and capital. The technical characteristics of intensive shrimp farming in the central provinces and the Mekong Delta are summarized in Table 5. Generally intensive shrimp ponds are rather small in area (0.2-0.5 ha) and may be lined for Pacific white shrimp culture. Stocking densities are greater for Pacific white shrimp (70-150/m2) compared to black tiger shrimp (20-35/m2). Pacific white shrimp culture with biofloc technology uses an even greater stocking density and requires a greater investment and is applied mainly in the central provinces. For intensive culture, water exchange is limited (Fig. 5d) and probiotics are commonly used for water management and health management. Pacific white shrimp are harvested after 90-100 days, with yields of 10-15 t/ ha per crop. Black tiger shrimp are harvested after 100-150 days, with yields of 3-7 t/ha per crop. The survival rate of shrimp is currently rather high although the industry has also been faced with the rather big issues of EMS, white spot and other diseases for several years. Intensive shrimp farming systems are currently operated under different organizational structures such as smallscale households, cooperatives, individual entrepreneurs and companies. Each production firm type has different advantages and disadvantages. The results of a survey indicated that production efficiency and linkages increase in the order of organizational type listed. Many large companies cover all TABLE 4. Technical aspects of the alternative rice-shrimp farming systems in the Mekong Delta (Minh et al. 2013). Parameters Unit Alternative rice-shrimp farming system Traditional system Improved system (Model 1) (Model 2) Farm area ha 2.7 ± 1.4 1.4 ± 1.5 Ditch area percent farm area 31 ± 8 26 ± 6 Ditch width m 3.4 ± 0.8 3.6 ± 0.6 Water level on platform m 0.34 ± 0.11 0.72 ± 0.13 Water level on ditch m 1.23 ± 0.36 1.50 ± 0.18 Stocking density PL/m2 2.2 ± 0.7 6.7 ± 1.6 Ratio of households testing shrimp seed percent 20 100 Ratio of households feeding shrimp percent 10 100 Ratio of households rearing postlarvae before stocking percent 50 90 Culture duration days 108 ± 21 117 ± 24 Shrimp BW at harvest g 30 ± 5 33 ± 9 Yields kg/ha/crop 232 ± 132 1,217 ± 611 TABLE 5. Characteristics of intensive shrimp farming in the central provinces and the Mekong Delta of Vietnam (Gam et al. 2014, Son et al. 2014). Central provinces Mekong Delta (Gam et al. 2014) (Son et al. 2014) Characteristic Pacific Pacific Black Pacific Black white shrimp white shrimp tiger shrimp white shrimp tiger shrimp (biofloc) (not biofloc) (not biofloc) Pond area (ha) 0.25±0.07 0.29±0.09 0.32±0.07 0.57±0.09 0.57±0.11 Pond depth (m) 1.40±0.22 1.23±0.10 1.21±0.08 1.42±0.23 1.28±0.10 Stocking density (PL/m2) 152±13 87±10 23±4 81±17 26±6 Culture period (days) 90±7 99±8 108±12 101±10 136±15 Harvest size (inds/kg) 80±7 78±5 41±6 52±8 32±7 Survival (percent) 84±6 82±4 76±13 81±14 76±20 FCR 1.24±0.56 1.32±0.08 1.52±0.55 1.17±0.08 1.80±0.18 Yield (t/ha per crop) 17.0±2.6 9.1±1.2 4.2±1.0 12.9±3.5 6.6±1.8
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