The Biofloc system or biofloc technology (BFT) was first developed in the 70’s in France with different shrimp penaeid species and, later, with tilapia. Nowadays, biofloc has been effectively practiced in shrimp and fish farming in Asia, Central and South America, the USA, South Korea, Brazil, Italy, China, and others.
The idea behind this approach came from the municipal wastewater treatment industry. In these treatment plants, microbes naturally growing in the human/animal waste are augmented with oxygen, food sources, and other beneficial microbes to transform the toxic wastes into less toxic organic products that can be safely returned to the environment.
With biofloc, the same core concepts are applied to aquaculture ponds. More specifically, BFT is the practice of enhancing beneficial bacteria growth in the aquaculture system, through three key actions:
- Adding extra carbon through external carbon sources or elevated carbon content of the feed as a food source for the beneficial microbes
- Limiting (or eliminating) water exchanges to allow microbial growth to remain, rather than filtering the water
- Increasing aeration to drive up dissolved oxygen levels and encourage aerobic bacteria growth
The Biofloc Layer
Suspended growth (bio floc) in ponds is a natural occurrence. In any pond, phytoplankton, bacteria, aggregates of living and dead particulate organic matter, and grazers of the bacteria can be found. With biofloc, these microorganisms are allowed to flourish – a major difference from traditional aquaculture.
But why is this a preferable approach?
BFT is considered an efficient alternative system because of the natural nutrient flywheel it creates.
If carbon and nitrogen are well balanced in the biofloc system, ammonia in addition to organic nitrogenous waste will be converted into bacterial biomass. By adding carbohydrates to the pond, heterotrophic bacteria growth (bacteria that obtains carbon from organic sources) is stimulated and nitrogen uptake for the production of microbial proteins takes place. However, organic carbon and inorganic nitrogen are generally taken up in a fixed ratio that reflects the needs of the specific bacterial found in the pond.
As with nitrogen assimilated by algae, the microbial protein produced by these heterotrophic bacteria can serve as a supplemental source of nutrition for fish and shrimp.
As a result, adopting biofloc techniques can:
- increase environmental control and biosecurity
- improve the maintenance of water quality
- reduce the feed costs
- improve fish/shrimp growth and disease resistance.
Biofloc & Biosecurity
Interest in closed aquaculture systems is increasing, mostly due to biosecurity, environmental, and marketing advantages over conventional extensive and semi-intensive systems. When water is reused, some risks such as pathogen introduction and the discharging of fish farm waste (pollution) are reduced or even eliminated.
BFT offers an advantage by eliminating water exchanges. With less water movement, opportunities for equipment and/or water to move between ponds are greatly reduced, preventing risks of pathogens spreading and leading to disease outbreaks. Also, by reducing water usage, water pollution is reduced as there is less affluent to leak back into the natural environment.
Biofloc and Ammonia Control
In addition to carbon, nitrogen is another food source for bacteria in these ponds. This nitrogen uptake decreases the ammonia concentration; often more rapidly than the traditional nitrification cycle. Immobilization of ammonia by these bacteria occurs much more rapidly because the growth rate and microbial biomass yield per unit substrate of heterotrophs are a factor ten higher than that of nitrifying bacteria.
In an aquaculture pond, a great deal of this excess nitrogen comes from the supplementary feeds provided to fish and shrimp. These feeds are rich in protein which contains up to 65% nitrogen content to drive stronger growth in the fish and shrimp.
However, traditional feeding is inefficient, with significant amounts of feed ending up un-eaten at the bottom of the pond. This uneaten feed is a great disease risk – serving as both a direct food source for harmful bacterial pathogens as well as an indirect risk as it breaks down into ammonia and creates poor water quality.
The increased microbial activity from BTF addresses this overfeeding problem, greatly reducing the disease and ammonia potential.
Biofloc and Reduced Feed Costs
These supplementary feeds are fundamental to modern production and account for between 60-80% of the total operating cost of an aquaculture operation. To control these feed costs, farmers and researchers have tried many approaches, including the addition of live feeds as an alternative to supplementary feeds.
In biofloc, the microorganisms themselves play a key role in augmenting the feed sources. In the water column, a complex interaction occurs between organic matter, physical substrate, and a large range of microorganisms such as phytoplankton, free and attached bacteria, aggregates of particulate organic matter, and grazers. The macroaggregates (biofloc) from these interactions are a rich protein-lipid natural food source available 24 hours per day. The natural microbial growth, as a result, creates a recycling process, consuming wasteful nutrients and converting them into protein-rich nutrients that the fish and shrimp can consume.
The consumption of the biofloc layer by shrimp and fish has been shown to have numerous benefits such as improvement of growth rate, a decrease of FCR, and lower associated costs in the feed. Growth enhancement has been attributed to both bacterial and algal nutritional components. In this context, biofloc has driven opportunities to use alternative diets, low protein feeds, and feeds with alternative protein sources different from marine-based products.
Biofloc and Improved Disease Resistance
With increasing intensification and reduced antibiotic usage, the disease is a key problem for the fish farming industry. Although vaccines are being developed and marketed, they cannot be used as a universal, cost-effective disease control measure.
As a result, new strategies in disease management in aquaculture have received much attention. Biofloc can be a good strategy for disease management. The presence of beneficial bacteria in the biofloc creates a “natural probiotic” effect, which can act both internally and externally to combat pathogens and improve immune response.
Probiotics are beneficial bacteria that play an important role in the microbial balance of the microbiome and the water environment. These natural biofloc probiotics, studies show, tend to mitigate the invasion of pathogenic bacteria, helping to improve the immunity of the fish and shrimp. Further evidence shows these beneficial bacteria significantly improve the nonspecific immunity of the animals cultured in the biofloc system.
Credit: Dr. Ishak Sharif