WWW.WAS.ORG • WORLD AQUACULTURE • DECEMBER 2014 25 (29-30 percent) feed. Grain pellets and molasses supply carbon as needed to sustain carbon-tonitrogen ratios greater than 15. Generally grain pellet applications vary from 15 to 20 percent of the total feed used during operations. Molasses can be applied two or three times weekly at 15-20 kg/ha. Water stability of grain pellets is between 15 and 20 minutes. This provides an inexpensive organic substrate for biofloc to develop, in addition to increasing the C:N ratio. Grain pellets are a mixture of ground wheat, corn and occasionally soy, with a protein level around 14-18 percent. Animalgrade ground wheat flour must be used. Using grain pellets from wheat flour as a carbon source results in better yield, survival and FCR of green tiger shrimp Penaeus semisulcatus (Megahed 2010). In addition to typical chemicals such as dolomite and lime, kaolin is required in the preparation of pond water and during operation. Kaolin is the mineral kaolinite, a hydrous aluminum silicate, also known as China clay. It is distinguished from other industrial clays on the basis of its fine particle size and pure color. Its ability to disperse in water makes it an ideal pigment. Fine particles of kaolin suspended in pond water are thought to become nuclei of bioflocs in pond water. Kaolin is applied at 50-100 kg/ha. Aerators help suspend bioflocs continuously in the pond water, a main requirement for maximizing the potential of microbial processes in shrimp culture ponds (Fig. 5). Especially in biofloc systems, aerators need to be constantly monitored for malfunctions and repaired or replaced without delay. Paddlewheel aerators keep dissolved oxygen levels high. Dissolved oxygen levels must be monitored frequently to keep levels greater than 4 mg/L. Water quality should be managed within the limits indicated in Table 2. Paddlewheel aerators need to be in the correct position to promote accumulation of sludge in central areas of ponds. Accumulated sludge at the pond center needs to be siphoned or drained out periodically as needed. The required energy input (horsepower of aerators) needs to be correlated to stocking density. High stocking densities of 130-150 post-larvae/m2 and high aeration rates of 28-32 hp/ha are also essential for expected production of over 20 t/ha. Aeration energy efficiency is 680 kg/ hp and can be as high as 1,000 kg/hp if partial harvesting is implemented. Performance of Biofloc Systems in Commercial Shrimp Farming The technology has been successfully applied commercially with shrimp (L. vannamei) by Belize Aquaculture (McIntosh 2001). Heterotrophic bacterial communities facilitate the production of high yields (~15 t/ha per cycle) in ponds with no water exchange. It has also been applied with success in commercial shrimp farming in Indonesia, achieving a production of nearly 50 t/ ha in small research and development ponds, and over 20 t/ha from commercial ponds, with feed conversion ratios between 0.98 and 1.30 (Table 3; Kopot and Taw 2004, Taw 2005, Taw 2010). A combination of two technologies, partial harvesting and biofloc, has been studied in northern Sumatra, Indonesia (Taw et al. 2008). Production performance using partial harvest with biofloc technology was greater than expected. One 2,500-m2 pond produced 12.4 t (49.5 t/ha) through six partial harvests, with a feed conversion ratio of 1.11. The technology was successfully commercialized in Malaysia (Taw et al. 2011). For ponds lined on dikes only, the shrimp farm averaged over 12 t/ha; for fully-lined ponds with a semi-biofloc system, the average was over 16.2 t/ ha. Two ponds with biofloc systems averaged over 22.5 t/ha with an average shrimp size of approximately 18 g. The outstanding achievement was in a biofloc system with a stocking density of 130 post-larvae/m2, where shrimp reached over 18.8 g in just over 90 days of culture, with a production of over 22.5 t/ha (Taw et al. 2011). A similar performance with a semi-biofloc system was recorded at the iSHARP project in Malaysia (Taw et al. 2013, Fig. 6). The small, family-owned Ndaru Luat Setio shrimp farm (CONTINUED ON PAGE 26) TOP, FIGURE 4. About 5 mL/L of settled biofloc in an Imhoff cone. Moderate floc densities are preferable. MIDDLE, FIGURE 5. Biofloc shrimp culture ponds must be well aerated. Note number and positioning of aerators. BOTTOM, FIGURE 6. Shrimp production in commercial-scale biofloc systems.
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