Water quality of tilapia cage culture in rural reservoir in São Paulo South, Brazil

Abstract

The study aimed to evaluate physical and chemical water conditions of a rural reservoir utilized for cage fish culture in Pariquera-Açu, SP. In this place, 20 cages of 4 m³ were installed and stocked with 150 tilapias per m³ during the period of 1^st February of 2008 to 1^st December of 2009. To determine reservoir water quality, five points of collection were analyzed every month: water supply, fish rearing area divided into three depths (10 cm, 70 cm and 150 cm) and effluent. Averages of analyzed parameters (± standard deviation) were: dissolved oxygen, 6.83 ± 0.7 mg O₂D L^-1; maximum and minimum temperature, 27.5 ± 0.9 and 17.6 ± 0.1°C respectively; hydrogenionic potential, 6.3 ± 0.1; transparency, 77.92 ± 15.5 cm; total alkalinity, 94.1 ± 4.0 mg CaCO₃ L^-1; electric conductivity, 47.84 ± 0.9 µS cm^-1; total ammonia, 0.004 ± 0.001 mg L^-1; nitrate and nitrite, 0.004 ± 0.001; and 0.009 ± 0.001 mg L^-1, respectively; total dissolved phosphorus and orthophosphate, 0.02 ± 0.01 and 0.004 ± 0.001 mg L^-1, respectively; total dissolved nitrogen, 0.21 ± 0.10 mg L^-1; chlorophyll a, 10.00 ± 0.08 µg L^-1, and suspended material, 0,013 ± 0,100 mg L^-1. The Calculated Trophic Estate Index was 49. It was concluded that tilapia cage culture did not compromise the water quality of rural reservoir, however animal production good practices and environmental monitoring should be followed for a sustainable fish culture according to CONAMA resolution.