Biofloc – The Key to Stress Resistance in Shrimp Farming?

Global demand for farmed shrimp is rising. Concurrently, the demand for sustainable shrimp farming practices is also rising. Spatial limitations are greater for shrimp culture than for fish; fish can occupy both a vertical and horizontal plane, while shrimp prefer the flat area at the bottom of a tank, resorting to cannibalism when placed too close to their neighbors. The area required to set up a nitrifying biofilter therefore presents a significant cost when growing shrimp in a recirculating system. Biofloc technology allows for water reuse without a separate nitrifying biofilter, instead placing the desired functional bacterial species directly in the rearing tank. Not only does this increase the amount of viable culture space, but bioflocs provide numerous other benefits that a biofilter does not.  

Microbial protein production is a steadily growing industry. These proteins are cheap, easy to produce, have a good nutritional profile, and are, broadly, environmentally friendly when compared with plant and animal alternatives. The nitrifying species that compose a functional biofloc convert carbon sources, such as simple sugars or leftover shrimp feed, and nitrogen waste into proteins to be consumed by shrimp. These have been observed to add 0.25-0.5 additional growth units for every one unit of commercial feed, previously, reducing both cost and feed production requirements. Some authors, such as Avnimelech (2015), have found a well-maintained biofloc system can reduce operating costs by 30%. Faster growth and tissue protein levels have also been observed.  

Microbial proteins and aggregates also provide health benefits beyond simple nutrition. Biofloc-consuming shrimp have increased resistance to industry critical pathogens, such as Vibrio parahaemolyticus. It is possible that the consumed biofloc has immunogenic or antimicrobial properties, as some microbial proteins do, or that the bacteria within the biofloc are colonizing the guts of farmed shrimp and creating a healthier hardier microbiome. Furthermore, Onda and its collaborators have observed reduced cannibalism and mortality during stressful activities, such as shrimp transfer, increased stocking density, and reduced water quality, even weeks after transferring biofloc-reared shrimp into clearwater systems.  

While biofloc technology has developed by leaps and bounds since its founding in the 1970s, it has yet to see truly widespread use. Bioflocs are more difficult to maintain than clearwater systems. Oxygen requirements are greater, as the heterotrophic species dominating the biofloc require aerobic respiration to perform their functions, and bacteria must be kept in suspension. Bioflocs cannot be allowed to grow unchecked either, as this will unfavourably increase total suspended solids and create an irritant to shrimp gills. Similar to RAS biofilters, achieving the appropriate microbial balance can be difficult, and making environmental adjustments may prove devastating to an unprepared farmer. Even so, the potential benefits of biofloc technology are too great to simply ignore.  

Avnimelech, Y. Biofloc Technology. A Practical Guidebook, 3rd ed.; The World Aquaculture Society: Baton Rouge, LA, USA, 2015.