Water quality in cage system fish farm in Ilha Solteira reservoir, SP

Abstract

The physical and chemical water variables and the sedimentation were evaluated in a tilapia culture with 240 cages (14 and 20 m³) located on 4.5 ha of water surface in the area of the Ponte Pensa river, in the aquaculture park of the Ilha Solteira reservoir. Monthly samplings were carried out from February 2008 to January 2010 in three sites: upstream (P1), in the place (P2) and downstream (P3) of the cages fish farm. The values of pH, total ammonia, nitrate, chlorophyll "a†and total dissolved solids remain within recommended by Resolution nº 357 of the National Council of Environment to water bodies for aquaculture. The lower dissolved oxygen concentrations were observed at the site P2 in almost all months, but the values were above 4.0 mg L^-1 and 60% saturation. The principal component analysis showed a trend of clustering of sampling units from the central area of the fish culture, because of the total dissolved solids concentration and sedimentation rate of total phosphorus, indicating that the fish culture directly influenced the increased levels of sediment. However, in general, the tilapia culture in cages caused a disturbance of low intensity in the aquatic system. The area of Ponte Pensa river proved efficient assimilation capacity of the disturbances caused by the production process, mitigating the impact of organic load from the feeding and fish metabolism.