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August 4, 2014
The July/August 2014 issue of Aqua Culture AsiaPacific contains an excellent article by Poh Yong Thong, general manager of nutrition and technical services at PT Gold Coin Indonesia, a shrimp feed company, on the basics of biofloc technology in shrimp farming. It’s a long article, covering current applications and recent developments, and it has lots of references
Here Are Some Excerpts from the Article
Indonesia may have the highest number of farms using biofloc or semi-biofloc technology in the world. Despite the many benefits of bioflocs, only about 20% to 25% of the shrimp farms in Indonesia are successfully using them, mostly in east Java and Bali and a few other scattered areas.
Advantages of Biofloc Systems: It is widely recognized that many of the deadly shrimp diseases such as whitespot virus, infectious myonecrosis virus and early mortality syndrome find it harder to infect shrimp grown in a biofloc systems. Wasielesky et al. (2013) showed that biofloc could be successful in preventing WSSV in Brazil.
Due to the vigorous aeration and agitation in biofloc systems, many of the solids from shrimp feces and uneaten feed are kept in suspension, thereby reducing sludge accumulation and sedimentation. A lethal concentration of Vibrio can be encountered in the water-sediment interface if sludge is left to accumulate. Tung and Le Poul (2014) suggested that it is best to remove solids two hours after every feeding. Almost 80% of the intensive shrimp ponds in Indonesia have a built-in sludge removal system. Some Indonesian farms deploy divers to siphon the sludge out of ponds. Experiments were conducted in Thailand that showed shrimp placed in a net pen elevated from the pond bottom did not become infected with EMS, even though other shrimp in the pond did become infected. The absence of heavy sludge in shrimp ponds may be the reason why EMS has not spread to Indonesia, despite its proximity to EMS-infected Malaysia.
Furthermore, since bacteria and not phytoplankton dominate biofloc ponds, the lethal opposing effect of high pH during the day and low pH during the night is neutralized. The pH stays stable. This in turn prevents ammonia spikes due to high pH when there is strong sunlight and hydrogen sulfide elevation due to lowered pH at night. Some aquaculturists prefer a pH fluctuation of less than 0.3 a day. This minimal magnitude of pH swing is an indicator that the biofloc contains some phytoplankton, which is beneficial for removing some of the nitrate (whose denitrifying process is optimal only in anaerobic conditions).
Disadvantages of Biofloc Systems: All biofloc systems require high dissolved oxygen (DO) of at least 4.5 parts per million due to the additional requirement by the biofloc and the need to physically keep it in suspension. Therefore, the most obvious disadvantage of these systems is the need for high oxygenation and hence high-energy cost in order to keep the shrimp as well as the biofloc in optimal condition. A power failure of just a few minutes could be lethal to the biofloc.
The highly oxygenated state is antagonistic to the anaerobic denitrifying bacteria that remove nitrate, resulting in decreased alkalinity and pH. Significantly higher skills and better-equipped laboratories are necessary to operate a biofloc system. Floc volumes, oxygen, pH, alkalinity, ammonia, nitrite and nitrate need to be constantly monitored.
Starting a Biofloc System: In general, in a highly oxygenated and agitated system with sufficient carbon inputs, biofloc will develop after 4-6 weeks, and alkalinity and pH will drop and nitrate will begin to accumulate. The sustainability of the biofloc cannot be ensured, and it may vary in form.
Conclusion: It is apparent that BFT offers many advantages for shrimp aquaculture. As the remaining knowledge gaps are gradually filled, bioflocs will—without doubt—contribute tremendously to aquaculture production through harnessing the power of nature, resulting in heightened efficiency, sparing valuable fish meal and fish oil, and reducing the use of precious water and land.
Source: Aqua Culture AsiaPacific (Editor/Publisher, Zuridah Merican, email firstname.lastname@example.org). Biofloc Technology in Shrimp Farming: Success and Failure. Poh Yong Thong (email email@example.com). Volume 10, Number 4, Page 13, July/August 2014.
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