Threshold environmental concentrations of cations defining the range of roach Rutilus rutilus L. in freshwater reservoirs

Abstract

Threshold levels of sodium, potassium, calcium, and magnesium that define the distribution range of roach in fresh water are 0.015–0.019, 0.012–0.015, 0.006–0.009, and 0.002–0.003 mmol/L, respectively. A reduction in water mineralization is accompanied by a significant decrease in the concentration gradient of cations between the organism of a fish and the environment and by the increased stress on the systems responsible for salty exchange. Many reservoirs are characterized by lower concentrations of potassium in the water than is needed for the success of the roach population. The survival of roach in these waterbodies depends on the amount of potassium consumed by fish with their food. A comparative analysis is performed to assess the threshold levels of cations for roach, two bivalve mollusk species, crayfish, and the filamentous algae Spirogyra.