Periphyton has an average C/N ratio of 10 (Azim and Asaeda, 2005). Its assimilation capacity is around 0.2 gN/ m2 day. From this it is clear that one needs a large surface, which allows periphyton growth, to treat intensive aquaculture wastewater without compromising the water quality. Besides N removal, biomass is formed. The yield is around 4 g dry matter/m2 day and the protein content of periphyton is around 25% of the dry matter (Azim et al.,2002, 2005). This corresponds to a particular feed quantity that can diminish the overall feed cost.