24 DECEMBER 2014 • WORLD AQUACULTURE • WWW.WAS.ORG Biofloc systems—a recent technology—offer a promise of stable and sustainable production, inasmuch as the system is operated without water exchange and so has an enhanced capacity for nitrification within the culture ponds (Avnimelech et al. 2012). The main economic advantages of biofloc technology over greenwater (algae-based) systems are higher growth rate, lower FCR and sustainable production (Table 2). Bioflocs are macroaggregates – diatoms, macroalgae, fecal pellets, exoskeletons, remains of dead organisms, bacteria, and invertebrates – suspended in the water column (Fig. 1). Biofloc can be used as a single-cell protein source for shrimp and fish. The crude protein content of biofloc ranges from 35 to 50 percent, and the crude lipid content is 0.6 to 12.0 percent by volume. Biofloc can be slightly deficient in arginine, lysine and methionine. The ash content ranges between 21 and 32 percent. In biofloc systems, algae develop first, then a transition period with foam formation and finally a brown biofloc develops (Fig. 2 and 3). This may take a few weeks or longer, depending on the biomass of shrimp or fish in the pond. The transition occurs earlier with tilapia, later with shrimp. Basically the systems starts with an algae bloom and the biofloc community develops thereafter. Advantages and Disadvantages One of the main advantages of biofloc technology is high biosecurity. To date, white spot syndrome virus has not been a factor in biofloc systems. Production and carrying capacity are typically Shrimp Farming with Biofloc Technology: Commercial Experience and Approaches to Disease Control Nyan Taw 5-10 percent greater than in typical culture systems with no water exchange. Shrimp grow larger and reflect feed conversion ratios between 1.0 and 1.3. Production costs can be 15 to 20 percent lower. A main disadvantage is the high energy input for aeration. Power failures of more than one hour in duration can be critical. Biofloc ponds need to be lined. The more advanced technology also demands better training of technicians. Brief Operating Protocol for Shrimp Farming Biofloc technology for shrimp culture on a commercial scale and in large ponds is simple and yet, in a way, complex. Basic conventional procedures, depending on location and situation of the farm, need to be followed. The procedure must be adjusted with changes in culture water environment and shrimp behavior, such as health and growth (Table 1). For optimized, sustainable commercial biofloc shrimp culture, HDPE- or concretelined ponds are basic requirements. Only specific pathogen-free post-larvae are stocked. When ponds are stocked, a major factor to be controlled is biofloc volume. Using Imhoff cones for assessment, biofloc volumes must be maintained below 10 mL/L for full biofloc and 5 mL/L for semi-biofloc systems (Fig. 4). A sample must be taken concurrently from each of two locations below the water surface. Green or brown water is acceptable, but black water is an indicator of abnormal conditions. Suspended biofloc must be available as food for shrimp. Shrimp can be fed high protein (35-40 percent) or low protein TOP, FIGURE 1. A biofloc macroaggregate. MIDDLE, FIGURE 2. Changes in the importance of algae and biofloc in a production cycle for shrimp. Algae is more important in the first half and biofloc dominates in the second half in response to high feed loading. BOTTOM, FIGURE 3. The transition from algae dominance to biofloc dominance in biofloc shrimp ponds is indicated by the presence of abundant foam.
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