By Ahmed Kabir, Institute of Marine science and fisheries, University of Chittagong, Chittagong, Bangladesh.
Mustapha ABA, Researcher Aquaculture Fish Nutrition Morocco.
Biofloc technology (BFT) is a technique for improving the quality of water in aquaculture by balancing carbon and nitrogen in the livestock system. It is a sustainable method for controlling water quality, with added value for microbial protein availability as a food source. From this process, the BFT system provides sustainable aquaculture that takes into account environmental, social and economic development aspects.
In addition to increasing the growth of heterotrophic bacteria, BFT provides bacterial proteins to animals, reducing the demand for dietary supplements, reducing feed costs by 30% for farmed aquatic animals, and also reduction of toxic nitrogen levels in livestock systems and effluents.
The need to reduce the environmental impacts generated by the disposal of nutrient and organic matter-rich effluents is fundamental for aquaculture. The BFT system appears as an alternative to conventional systems to minimize effluent emissions. As a result, the BFT system is a sustainable and environmentally friendly system, minimizing the environmental impacts of nutrient-rich effluents and organic matter discharge, as well as minimizing the use of water for the environment. as well as an optimization of water use of 90%, knowing that water is an aquaculture source that is becoming increasingly rare in Africa.
Biofloc system a good technology of Aquaculture : What is it and how it works?
It is an innovative and cost-effective technology in which toxic materials to the fish and shellfish such as Nitrate, Nitrite, Ammonia can be converted to useful product, ie., proteinaceous feed. It is the technology used in aquaculture system with limited or zero water exchange under high stocking density, strong aeration and biota formed by biofloc. The culture of Biofloc will be productive in the case of culture tanks exposed to sun.
Biofloc System :
Biofloc system was developed to improve the environmental control over the aquatic animal production. In aquaculture, the strong influential factors are the feed cost (accounting to 60% of the total production cost) and most limiting factor is the water/land availability. High stocking density and rearing of aquatic animals requires wastewater treatment. Biofloc system is a wastewater treatment which has gained vital importance as an approach in aquaculture.
The principle of this technique is the generation of nitrogen cycle by maintaining higher C: N ratio through stimulating heterotrophic microbial growth, which assimilates the nitrogenous waste that can be exploited by the cultured species as a feed. The biofloc technology is not only effective in treating the waste but also grants nutrition to the aquatic animal.
The higher C: N is maintained through the addition of carbohydrate source (molasses) and the water quality is improved through the production of high quality single cell microbial protein. In such condition, dense microorganisms develop and function both as bioreactor controlling water quality and protein food source. Immobilization of toxic nitrogen species occurs more rapidly in bioflocs because the growth rate and microbial production per unit substrate of heterotrophs are ten-times greater than that of the autotrophic nitrifying bacteria. This technology is based on the principle of flocculation within the system.
The biofloc technology has been implemented in shrimp farming due to its bottom dwelling habit and resistance to environmental changes.
Composition and Nutritional Value of Biofloc:
Biofloc is a heterogeneous aggregate of suspended particles and variety of microorganisms associated with extracellular polymeric substances. It is composed of microorganisms such as bacteria, algae, fungi, invertebrates and detritus, etc. It is a protein-rich live feed formed as a result of conversion of unused feed and excreta into a natural food in a culture system on exposure to sunlight. Each floc is held together in a loose matrix of mucus that is secreted by bacteria and bound by filamentous microorganisms or electrostatic attraction. Large flocs can be seen with the naked eye, but most of them are microscopic. Floc size range from 50 – 200 microns.
A good nutritional value is found in biofloc. The dry weight protein ranges from 25 – 50 percent, fat ranges 0.5 – 15 percent. It is a good source of vitamins and minerals, particularly phosphorous. It also has an effect similar to probiotics. The dried biofloc is proposed as an ingredient to replace the fishmeal or soybean in the feed. The nutritional quality is good; however, only limited qualities are available.
Benefits of Biofloc Culture System:
- Eco-friendly culture system.
- It reduces environmental impact.
- Improves land and water use efficiency.
- Limited or zero water exchange.
- Higher productivity (It enhances survival rate, growth performance, feed conversion in the culture systems of fish).
- 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 ie., use of cheaper food fish and trash fish for fish feed formulation.