Carbon nitrogen ratio as a control element in aquaculture systems

Controlling the inorganic nitrogen by manipulating the carbon/nitrogen ratios is a potential control method for aquaculture systems. This approach seems to be a practical and inexpensive means of reducing the accumulation of inorganic nitrogen in the pond. Nitrogen control is induced by feeding bacteria with carbohydrates, and through the subsequent uptake of nitrogen from the water, by the synthesis of microbial proteins. The relationship among the addition of carbohydrates, the reduction of ammonium and the production of microbial proteins depends on the microbial conversion coefficient, the C/N ratio in the microbial biomass, and the carbon contents of the added material. The addition of carbonaceous substrate was found to reduce inorganic nitrogen in shrimp experimental tanks and in tilapia commercial-scale ponds. It was found in tilapia ponds that the produced microbial proteins are taken up by the fish. Thus, part of the feed protein is replaced and feeding costs are reduced. The addition of carbohydrates, or the equivalent reduction of proteins in the feed, can be quantitatively calculated and optimised, as shown here. Approximate parameters were used in this work. Additional research in this field should be directed at gathering the precise data needed for the exact planning of feed composition. (C) 1999 Elsevier Science B.V. All rights reserved.