“Biofloc technology is considered the new “blue revolution” in aquaculture.”

Biofloc Technology (BFT) is a new revolutionary tool for water quality management and nutrition in aquaculture (check out our blog on Bioflocs in Aquaculture).

BFT is based primarily on in situ microorganism production. This plays three major roles:

It helps with maintenance of water quality by the uptake of nitrogen compounds
It increases aquaculture feasibility by improving nutrition, reducing feed conversion ratio (FCR), and a decreasing feed costs
It mitigates external pathogens through competition

This technology is used for several aquacultured species in ponds and tanks, where the aquatic environment can be more easily controlled.

To stimulate this natural bacterial production, the right mixture of nutrients and microorganisms must be present. Carbon is a particularly important nutrient for biofloc effectiveness because it is used as food sources for the bacteria that are important in biofloc (or zero-water-exchange) farming.

In this blog, we explore the various carbon sources available to help you determine the right carbon source for your biofloc system.

What are bioflocs?

Bioflocs are aggregates of a rich protein-lipid source of food, which is natural and always available in situ. This is due to a complex interaction between organic matter, substrate, and a large range of microorganisms. This natural productivity plays an important role recycling nutrients and maintaining the water quality.

The management of the carbon-to-nitrogen ratio (C:N) in BFT is normally divided in two phases: the initial or formation phase and the maintenance phase. During the formation phase, the C:N ratio should be between 12:1 and 20:1, whereas in the maintenance phase this should drop to around 6:1, according to the total ammonia nitrogen (TAN) values.

In the initial phase, the high carbon-to-nitrogen ratio is a key factor to promote and stabilize the heterotrophic community within the pond. Higher carbon concentrations will induce the nitrogenous by-product assimilation by heterotrophic bacteria — and will also supersede the carbon assimilatory capacity of algae, which will enable bacteria growth. The system is usually considered to be mature after about 30 to 50 days.

While the production cycles advance through maturity, chemoautotrophic bacteria will continually nitrify the water — and suspended biofloc particles will also continue to increase over time. In order to control these levels, carbon addition needs to be reduced or even stopped. This will prevent an excess of bioflocs in the aquaculture system and excessive DO consumption, which will negatively impact fish.

For the maintenance phase, the monitoring of TAN values is an important tool for water quality maintenance. When values of TAN are higher than 1.0 mg L−1, increasing the addition of carbon sources is helpful — with a C:N ratio of 6:1.

In this phase, the use of monosaccharide and oligosaccharide carbohydrate-rich sources (e.g. corn starch, molasses, other sugars) is ideal. This is due to the faster bacteria assimilation, which will result in TAN reduction. It is important to note that the carbon content will change according to the dry matter composition and type of carbon source.

It is also important to select the right carbon sources for optimal biofloc output.

Main sources of carbon in biofloc ponds

The carbon sources applied in BFT are often by-products derived from human and/or animal food industry, preferentially cheap and local available. Cheap sources of carbohydrates such as molasses, glycerol, and plant meals (i.e., wheat, corn, rice, tapioca, etc.) will be applied before the fry/postlarvae stocking (fertilization protocols) and during grow-out phase, aiming to (i) provide food for the first stages of growth and (ii) to maintain a high C:N ratio and to control N-compound peaks in the culture tanks, respectively.

Depending on which carbon source is used, bacteria assimilation characteristics will certainly need to take into account. Monosaccharides, or simple carbohydrate-rich sources (such as glucose, sugar, or molasses) are much different than polysaccharide, or complex carbohydrate-rich sources (such as corn starch and rice bran) and will confer different bacteria assimilations, nutritional values, and growth patterns. In addition to price differences, each carbon source will lead to different nutritional values within biofloc ponds.

Different carbon sources should be chosen for the initial phase versus the maintenance phase — with price and purpose being significant factors in which source is chosen for each phase. Grains and tubercles contain high levels of carbohydrates, which are essentially carbon, that are comparable to polysaccharides and sugars. But some carbon sources contain additional components, such protein and lipids. For example, corn meal contains 11.79% protein and 2.8% lipids; meanwhile, wheat flour is made of 15.5% protein and 3.73% lipids. Monosaccharides without protein and lipid have been shown to promote the best growth and the highest protein content into the tilapia tissue. It is possible that the chemical structure of sugar presented a high bioavailability to heterotrophic bacteria, hence, fast increase of bacterial biomass.

Below are several commonly used carbon sources for biofloc production.

Corn starch
Corn starch is often used in biofloc ponds as it is a great probiotic and promotes optimal ratios during both the initial and maintenance phases of BFT. It is a popular choice because of its efficacy and ease of access. Here’s a link to a recent study on why corn starch is preferable to molasses.

Molasses and sugar
Molasses and sugar are both good sources of organic carbon, with C:N ratios between 10:1 and 20:1. Using molasses in BFT systems can reduce the cost of production, but it is not easily accessible in many regions around the world.

Tapioca
Tapioca is a flour made from cassava and is very popular in many parts of the world, such as Brazil and Mexico. It is one of the most naturally carbohydrate-rich food products in the world and is easily accessible in many regions, such as the Americas.

Rice bran
Rice bran is a useful carbon source because rice is such a ubiquitous food that can be found all over the world. It’s ease of access is attractive, though it is less effective in BFT than corn starch, molasses, or tapioca.

Advantages and disadvantages of BFT

There are major advantages for using the aforementioned carbon sources in BFT when compared with recirculating aquaculture systems (RAS). However, there are some downsides to this method, depending on the time and energy available. Below is a table that summarizes the best and less ideal aspects of using BFT.

Cons

Increased energy requirement for aeration
Reduced emergency response time because water respiration rates are elevated
Start-up period required
Alkalinity supplementation required
Increased pollution potential from nitrate accumulation
Less sensitivity to light fluctuations

Pros

Improved biosecurity
Improved feed conversion
Improved water use efficiency
Increased land-use efficiency
Improved water quality control
Reduced sensitivity to light fluctuations (weather)

Benefits of using PowerFloc™ in BFT

We’ve designed PowerFloc™, our biofloc probiotic for fish and shrimp, to not only provide the necessary bacterial boost your system needs, but also provide a high-performing carbon source to accelerate your floc development. PowerFloc™ is composed of 10 B CFU/g of enzyme-producing probiotics blended on high-quality corn starch, a clean carbon source. Click here to learn more about this product and how it can help you catch the blue revolution.

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