The Israeli Journal of Aquaculture - Bamidgeh 55(4), 2003
The 7th Annual Dan Popper Symposium


Micha Eshchar, Noam Mozes, Michael Fediuk, Adi Peduel, Mirit Gada, Keren Bressler and Benny Ron*

Israel Oceanographic and Limnological Research Ltd., National Center for Mariculture, P.O.Box 1212, Eilat 88112, Israel


One of the major production costs in recirculating systems is the removal of ammonia to maintain a sub-toxic concentration. This research, financed by the Chief Scientist of the Ministry of Agriculture, suggests an innovative and generic approach. It may allow the total ammonia nitrogen (TAN) concentration to be greater by an order of magnitude than conventional concentrations for fish growth. The main principle is that the fraction of toxic unionized ammonia (UIA) of the TAN, inversely depends on the pH of the water. As CO2 excreted by fish lowers the water pH, the UIA fraction is reduced. Theoretically, this may allow the elevation of TAN to high concentrations. Prospected benefits of this approach are considerable savings in investment costs in biofilters in recirculating systems and a significant reduction of water consumption in flow-through systems. Another advantage may be reduction of the environmental impact through higher nitrogen assimilation rates in algae ponds that treat fish tank effluents.

Last year, experiments were conducted in the engineering and physiology departments at NCM. Gilthead sea bream (Sparus aurata ) were reared in high ammonia concentrations. The fish tested in the physiology department were 1 g, whereas those tested in the engineering department weighed 40-80 g. In low pH (£7.0-7.1), fish may be reared in TAN concentrations 5- 10 times higher than conventional levels without a significant reduction in fish growth performance. When the make-up sea water flow in a flow-through system was about 20% of the rate in conventional systems, fish grew without a biofilter. Equations were developed to show the relationship between inputs such as feed, the CO2-stripping and water exchange rates and water quality parameters such as pH, TAN, UIA, CO2 and alkalinity.