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 toxic ammonium. With 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 that 20% of protein eaten by shrimp or fish growing in BFT systems came from bio flocs harvesting.