IET for the environmental monitoring of the intensive production of tilapia in cage in the Atlantic forest region of South America

The production of tilapia (Oreochromis niloticus) in cages requires the constant monitoring of the physical and chemical water properties, since it is an activity considered potentially polluting for the aquatic environment and its monitoring is fundamental to avoid the water body eutrophication processes. The present study was conducted in a reservoir located in a fishfarm at Pariquera – Açu County (São Paulo state, Brazil) and evaluated the influence of the intensive Nile tilapia production in cages on the trophic state and in the water quality. For the trophic state determination, five classes were considered and stablished by the Trophic State Index (TSI). The trial was developed and divided in three phases: before (90 days), during (180 days) and after (90 days) the fish intensive production in the reservoir. Thirty net cages with volume of 4 m³ and stocking density of 150 fish per m³ were installed. According to the results, it was observed that the trophic state index (TSI) was increasing according to the production period, changing from an ultra-oligotrophic to a mesotrophic state, reaching a maximum value of 53.2 ± 0.4, and, after production period, remained oligotrophic. The water quality parameters did not present significant differences between the periods analysed (P>0.05). The implementation of the TSI represents a practical tool for environmental monitoring and risk analysis of fish production in the aquatic environment.