Freshwater parameters in the state of Rio Grande do Sul, southern Brazil, and their influence on fish distribution and aquaculture

ABSTRACT This study analyzed the relationship between several water quality parameters (pH, hardness, alkalinity, turbidity, iron and manganese) levels measured over a 16 year period with fish distribution and aquaculture in the state of Rio Grande do Sul, Southern Brazil. The mean pH values were within a neutral range (6.5-7.5), but the maximum and minimum values reached inappropriate levels for fish farming in some cities. Alkalinity levels were very low (except in the southwest region of the state), which may have contributed to pH variation. Hardness, turbidity, iron (except the region near Caçapava do Sul City) and manganese were within safe ranges for fish farming; however, turbidity levels occasionally increased to levels outside the safe range. In conclusion, the water quality in the Rio Grande do Sul, in general, can be considered adequate for aquaculture, but the fish farmers must be aware of the methods to reduce turbidity, such as the use of calcium sulfate