Avnimelech (1999) pointed out the use of the C/N ratio as a control element in aquaculture systems. Nitrogen controlwas induced by adding carbohydrates to thewater,and through the subsequent uptake of nitrogen by heterotrophic bacteria. This resulted in the synthesis of microbial proteins that can be eaten by the cultured fish
species. Experiments with sediment suspension amended with about 10 mg N/L ammonium and glucose at a concentration 20 times higher than that of the TAN showed that almost all the added ammonium disappeared over a period of about 2 h.Avnimelech et al. (1994) found that protein utilization by fish in intensive bio-floc systems is almost twice as high as the protein utilization in conventionally fed intensive aquaculture ponds, due to a recycling of the excreted nitrogen into utilizable microbial protein. Protein recovery by tilapia rose from 23% in the control to 43% in the floc treatment. It was concluded from this study that the price of feed for fish production using sorghum supplemented granules (pellets containing only 20% protein and sorghum as a carbonaceous substrate) is just about 50%of the conventional cost when 30% protein pellets were used.