Waste water treatment for reuse in hatcheries (Recirculating Aquatic System -RAS) are facing problems arising from the salinity, low ammonium concentration and the requirement of high purification degree. Under such conditions, rate of the whole process is inhibited, rendering a high capital cost for treatment system. Labor research was implemented to assess the impact of salinity on the nitrification and denitrification performing in fixed bed reactor using porous carrier and the nitrogen removal efficiency from water medium. Results achieved showed salinity of low content did not rnarkly influence on the nitrification as the case of high salinity while denitrification was mostly independent on the salt content for a wide concentration range. The influence of carrier size on nitrification and denitrification was also investigated in order to determine appropriate conditions for treatment purposes.