Bio Floc Technology (BFT) is a new approach toward management of ponds, in most cases intensive tilapia or shrimp ponds. Water scarcity, the demand for bio-security and economy, all leads to minimizing water exchange, even down to zero. Under these conditions, a major problem is the accumulation of ammonia and nitrite, both toxic to shrimp and fish. One way to solve this is to recycle the water through a bio-filter system. Recirculating Aquaculture Systems (RAS) are known to work well, yet they have two major problems: First they are expensive in both investment and maintenance and secondly, they recycle water but do not recycle feed residues. Feed is becoming more and more expensive and its recycling is essential.
An alternative approach, the Bio Floc Technology (BFT) is based upon the activity of the microbial community within the pond. Water treatment is done within the pond, with no need for a separate water treatment compartment. Very dense microbial community develops when water exchange is limited. Typically, we find 10-1000 million microbial cells (107-109) in 1 cm3 of pond water. If we add carbonaceous material (molasses, starch, tapioca and others) to adjust the C/N ratio in feeds to 15-20, the microbes take up the ammonium from the water and create microbial protein. By the adjustment of the C/N ratio, the nitrogen problem can be easily and consistently solved as described and formulated by Avnimelech (1999).
An important feature of BFT is the ability to recycle proteins. In conventional aquaculture, only about 20-25% of feed protein is retained by fish or shrimp. The rest is excreted to the water, mostly as ammonium. In BFT the ammonium is converted to microbial protein (through the addition of carbohydrates), that can be used as a protein source. The micro-organisms in the water tend to aggregate and form bio-flocs that can be filtered and harvested by tilapia or shrimp. It was found, using 15N tagging of bio flocs, that more that 20% of protein eaten by shrimp or fish growing in BFT systems comes from bio flocs harvesting. The amount of feed protein retained in BFT systems is double than that in traditional ponds, since the protein is practically used twice: Once when pellets are eaten by fish and then when the bio flocs are harvested. The doubled feed efficiency is a very important factor, especially now, when feed costs are rising. Both protein recycling and water quality control are achieved through the addition of carbonaceous feed and adjustment of the C/N ratio.
Extensive work had been done on the composition and nutritive value of the flocs. A detailed work by Tacon and coworkers (2003) demonstrated the presence of more than 30% protein, containing essential amino acids in sufficient quantities. In addition, it was demonstrated that the microbial flocs contain vitamins and trace metals enabling to omit those from the feed, saving about 25% of the Protein is an expensive feed component. In addition, it is, at least partially, made of fish meal, a component that is scarce and its harvest in the ocean leads to environmental damage. Thus, the fact that protein utilization rises from 15-25% in conventional ponds to 45% in BFT is very important. The utilization of microbial flocs as a source of feed protein leads to a lower expenditure on feed. Avnimelech reported that feed cost for tilapia production was lowered from $0.84/kg fish in conventional ponds to $0.58 in BFT. McIntosh reported that feed cost using the lowered protein diet in Belize Aquaculture was about 50% as compared to conventional shrimp farming.
BFT systems are environmentally friendly, mostly due to the fact that there is almost no release of nutrient rich drainage water to the environment. According to existing calculations and farm experience, BFT is a way to grow shrimp or fish (tilapia) in a profitable way, saving in investment and maintenance and lowering disease outbreaks.