A Revolutionary System of Biosecured Semi-intensive and Intensive shrimp and Fish Farming.

Biofloc technology has become a popular technology in the farming of Pacific white shrimp, Litopenaeus vannamei and now it is used in P. monodon, Tilapia and other fish farming. It is now a very popular system of semi-intensive and intensive shrimp and fish farming with low or no water exchange. It is comparatively much profitable and bio-secured system of aquaculture. The basic technology was developed by Professor Yoram Avnimelech (2000, 2005a&b) in Israel .This system is commercially using with success in shrimp farming in Indonesia, Malaysia and Australia.

This technology utilizes the co-culture of heterotrophic bacteria and algae grown in flocs under controlled conditions within the culture pond. Thus microbial biomass is grown on unconsumed feed, fish excreta, and inorganic nitrogenous products resulting in a removal of these unwanted components from the water. The major driving force is the intensive growth of heterotrophic bacteria which consume organic carbon . It has been calculated that a carbohydrate need of 20g to immobilize 1 g of N, based on a microbial C/N ratio of 4 and a 50 % C in dry carbohydrate.
Flocs consist of a heterogeneous mixture of microorganisms (floc formers and filamentous bacteria), particles, and colloids.
At its core, biofloc is a waste water treatment system and was developed to mitigate the introduction of diseases into aquaculture facilities or farms from incoming water (water exchange, typically used in prawn farming). Biofloc systems employ a counter-intuitive approach to more traditional aquaculture designs. Where more traditional aquaculture designs seek to remove suspended solids, bio-floc systems allow and encourage solids and the associated microbial communities to accumulate in the water. Assuming sufficient aeration and amalgamation in order to maintain an active “floc” in suspension, water quality can be maintained and controlled. Bioflocs’ may also have probiotic effects in some species. Essentially, bioflocs’ provide two very critical services which also helps a little to understand how they work. They treat wastes from feeding and provide nutrition from floc consumption. “Flocs” are a supplementary food resource that can be consumed between feeding times (pellet use). One of the benefits of biofloc systems is it capacity to recycle waste nutrients via microbial protein into fish or prawns. The main component of biofloc is nitrogen that is incorporated into bacterial cells. One other benefit of biofloc systems is the benefit of improved feed conversion ratios derived from the consumption of microbial protein. It should also be noted that bi-floc systems are generally implemented as pond based systems as they add the most benefits to pond based aquaculture. Additionally, biofloc is not suitable for just any species and works best with species that are able to derive nutritional benefit from the direct consumption of “floc”.

Biofloc Management:

The major component of biofloc is heterotrophic bacteria. The function of the biofloc is to reduce the nitrogenous metabolic waste (ammonia, nitrite) produced by shrimp feeding and production.
Ammonia consumed by heterotrophic bacteria becomes protein, which can then be consumed by shrimp and converted into growth. Heterotrophic bacteria need carbon for ammonia to be assimilated. In addition to the commercial feed, a supplemental source of carbon must be added in order to stimulate production of the heterotrophic bacteria and reduce the nitrogenous waste.Shrimp feed has a carbon to nitrogen (C:N) ratio of approximately 7–10:1. Heterotrophic bacteria would prefer a ratio of approximately 12–15:1. Simple sugars or starches are added to increase the ratio and promote bacterial growth. Additives have included molasses, sugar, sucrose, and dextrose. Some producers use glycerin. Application rates will vary with the protein content of the feed and composition of the carbon source, but a good rule of thumb is that for every 1 kg of feed, about 0.5–1 kg of carbon source is required. Higher protein feed will need higher carbon supplementation. Actual applications must take into consideration the levels of ammonia and nitrites in the water.
For successful and efficient management of a biofloc farm have to get more idea about biofloc management. But the technique is not so complicated. Most simple and easily understandable explanation about biofloc is that heterotrophic bacteria will decompose waste materials and ammonia content of water and will be converted to bacterial biomass. Part of this highly nutritious biomass consumed by protozoa and other microorganisns will converted to their biomass. These microorganisms and bacteria remain in small floc and serves as very nutritious food of the cultured organisms. So biofloc system helps to maintain good water quality , decreases requirement of water exchange, decreases quantity of feed requirement(by about 20%) and helps to maintain biosecurity
Biofloc system of farming is now very popular in many countries of the world including Indonesia, Vietnam, Thailand, India etc.

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