The permissible limits of chemical parameters are used as an indication for water quality deterioration in fish breeding. The permissible limits identified by some countries for ammonia is approximately 0.1 ppm and about 10 ppm for nitrite. Besides the control of water quality with respect to the above two parameters, attention should also be directed to the accumulation of nitrate and other organic substances. According to experiences made in rearing systems, the acceptable concentration may be 200 ppm for nitrate and 40 ppm for COD.