Periphytic biomas in net cages of Nile tilapia - Oreochromis niloticus (Linneau, 1758).

The aim of this study was to evaluate the biomass of the periphytic community in aquaculture net cages of Oreochromis niloticus. We determined the time required to stabilize this community and contributed to the knowledge of its potential to sustain the fish production. For this, 15 net cages were set in an arm of the Rosana Reservoir (Paranapanema River), the Corvo River. In these net cages, artificial substrates were used to allow the development of the periphytic community, which had its biomass monitored fortnightly, indexed as chlorophyll-a, dry weight, ash-free dry weight and percentage of ash. The biomass of periphytic community found in the net cages of the Corvo River was high. In fact, it was higher than the values already reported by other authors in a variety of cultivation systems. Considering chlorophyll-a, the time for the community be considered mature, with uniform pattern of colonization and maximum concentration was four weeks. The knowledge of this time, necessary for the stabilization of the periphytic community, is of great importance to aquaculture. The use of this community as natural food may contribute to the sustainable management of systems and reduce costs for the producer, with reduction of the use of commercial food, for the environment with less addition of nutrients.