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  • Writer's pictureAkhilesh Sachan


Use of Molasses in aquaculture to control ammonia and also for biofloc farming: How molasses works and how biofloc is formed?

Comment: Easy description for the learners.


Use of molasses in normal aquaculture:

A healthy aquaculture environment is a living, breathing ecosystem that relies heavily on heterotrophic bacteria to remove wastes and optimize feed conversion ratios. In order to maintain a healthy aquaculture environment, heterotrophic bacteria need to be encouraged to thrive through means both natural and artificial.

What are heterotrophic bacteria?

Heterotrophic is the term given to describe bacteria that derive nutrition from sources that are primarily organic. Heterotrophic bacteria include both probiotic and pathogenic bacteria types. Probiotic and pathogenic bacteria both naturally occur in aquaculture environments. As their primary source of nutrition is organic compounds, heterotrophic bacteria are exceptionally useful in breaking down organic wastes produced by fish/shrimp.

Heterotrophic bacteria rely on two nutrients to thrive, Nitrogen and Carbon. As anyone in the aquaculture Nitrogen is in abundance in a pond environment. Fish/shrimp wastes are extremely rich in Nitrogen, which, when in excess can lead to dangerous water chemistry problems increasing unionized ammonia.

With Nitrogen in abundance, growth of heterotrophic bacteria is limited by the amount of carbon that is available to consume. The goal of optimizing carbon: Nitrogen ratios (C: N Ratio) is to increase the level of carbon to an appropriate ratio to allow heterotrophic bacteria to thrive. If this is achieved, then the bacteria will be able to break down the Nitrogen-rich wastes and reduce the ammonia content in the water and water will be almost free from ammonia.

Encouraging Growth of Heterotrophic Bacteria:

To promote the growth of heterotrophic bacteria it is necessary to boost the amount of carbon that is available for heterotrophic bacteria to consume. A significant amount of additional carbon needs to be introduced into the water of the pond. Those carbons are more readily assimilated by the bacteria.

One of the cheapest most effective means of introducing carbon to the water column is by adding molasses. Molasses is a wonder additive for aquaculture; because it is largely carbohydrate in nature, contains a great deal of carbon and does not contain Nitrogen. Adding molasses to the water will boost carbon levels quickly and more importantly increase the carbon side in the ratio of Nitrogen to Carbon.

Daily in-the-field testing of ammonia is standard practice so trials looked at molasses dosing based solely on TAN concentration (32 g molasses/g TAN in the pond), plus doses based on double that amount to account for the extra 'unmeasured' bio-available Nitrogen present (64 g/g TAN).

The claimed improvement at the test site was within six hours, 65% of the TAN was removed from the water table with the lower dose of molasses. The reaction could not reach its conclusion as the entire dosage of molasses was consumed. The larger dose eliminated almost all of the TAN in the aquaculture pond.

The process of bacterial reproduction and consumption of Nitrogen and Carbon is aerobic. In order to achieve the best results, the aquaculture pond will need to be aerated. Aeration will greatly improve the speed of reproduction and prevent any anaerobic activity which can have a negative impact on water quality.

Bacteria tend to flocculate around suspended particles and become part of the food cycle for aquatic life. Flocculated bacteria provide a rich source of protein for fish life and can reduce feeding requirements. If there is too much organic matter on the surface, however, one will need to periodically drain it in order to maintain water quality.

Certain enzymes can be introduced in addition to the molasses that will bond with the carbon and render it easier for the heterotrophic bacteria to consume. This has the effect of both increasing the speed of the reaction and allowing the reaction to take place more fully, with less wastage.

Treatment with Enzymes:

There are a number of different enzymes that can be used to assist in the breakdown and simplification of organic wastes in the pond. These enzymes will target specific organic compounds in the water which includes carbon and various Nitrogen-based contaminants.

By optimizing C: an N ratio in conjunction with breaking down organics is a simple, safe and effective means of improving water quality.

Using enzymes in conjunction with molasses has the additional benefit of breaking down the organic matter that builds up as a result of the bacterial growth encouraged by adding molasses. Using enzymes in conjunction with molasses will help to limit the amount of times that the bacterial-floc needs to be drained.

Use of molasses in Biofloc system of farming to control of ammonia and production of bioflocs:

Biofloc is a heterogeneous aggregate of suspended particles and variety of microorganisms associated with extracellular polymeric substances.

In biofloc system of farming higher C: N is maintained through the addition of carbohydrate source (molasses) and the water quality is improved through the production of high quality bioflocs. In such condition, dense microorganisms develop and function both as bioreactor controlling water quality and protein food source.

Bioflocs are aggregates (flocs) of algae, bacteria, protozoans, and other kinds of particulate organic matter such as feces and uneaten feed. Each floc is held together in a loose matrix of mucus that is secreted by bacteria, bound by filamentous microorganisms, or held by electrostatic attraction .The biofloc community also includes animals that are grazers of flocs, such as some zooplankton and nematodes. Large bioflocs can be seen with the naked eye, but most are microscopic. Flocs in a typical green water biofloc system are rather large, around 50 to 200 microns, and will settle easily in calm water.

The nutritional quality of biofloc to cultured animals is good but rather variable. The dry-weight protein content of biofloc ranges from 25 to 50 percent, with most estimates between 30 and 45 percent. Fat content ranges from 0.5 to 15 percent, with most estimates between 1 and 5 percent. There are conflicting reports about the adequacy of bioflocs to provide the often limiting amino acids methionine and lysine. Bioflocs are good sources of vitamins and minerals, especially phosphorus. Bioflocs may also have probiotic effects. Dried bioflocs have been proposed as an ingredient to replace fishmeal or soybean meal in aquafeeds

Benefits of use of molasses and Biofloc Farming.

• Eco-friendly culture system.

• It reduces environmental impact.

• Improves land and water use efficiency.

• Limited or zero water exchange

• Higher productivity

• Higher biosecurity..

• Reduces water pollution and the risk of introduction and spread of pathogens.

• Cost-effective feed production.

• It reduces utilization of protein rich feed and cost of standard feed.

• It reduces the pressure on capture fisheries i.e., use of cheaper food fish and trash fish for fish feed formulation.

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