The influence of pH, dissolved oxygen, suspended solids or dissolved solids upon ventilatory and cough frequencies in the bluegill Lepomis macrochirus and brook trout Salvelinus fontinalis

Abstract

Conservative no-effect concentration ranges were estimated for ventilatory and coughing responses of bluegill sunfish Lepomis macrochirus and brook trout Salvelinus fontinalis exposed to altered pH, or to changes in dissolved oxygen (DO), suspended solids, or dissolved solids concentrations. These limits predict safe, or non-alarm-causing, variations of these non-toxic environmental variables in applied biomonitoring systems using Lake Superior or similarly constituted waters as a dilution source. Bluegill ventilatory and coughing responses were slightly more sensitive than those of brook trout. Bluegills showed increased ventilatory frequency in dissolved oxygen concentrations below 77% air saturation, pH 6·7 and below, and hardness of 190 mg litre −1 (as CaCO 3) or higher, but no increase in ventilation in suspended solids concentrations up to 323 NTU of clay particles. Brook trout responded with increased ventilation only in concentrations of DO at 44%, pH of 6·0 and 231 NTU suspended solids. Ventilatory frequency responses at low pH were attributed to increased free CO 2 released by acidification of the dilution water. Over the DO range tested (44–117%) coughing was unaffected in both species. Bluegill coughing increased at pH levels above 9·0, but not below the control pH of 8·0. Increases also occurred in some suspended solids concentrations (90 NTU and above) and in hardness of 190 mg litre −1 and above. Brook trout coughing was unaffected over the pH range 5·1–10·1 and at all suspended solids (0·6–318 NTU) concentrations tested. The only coughing response observed for brook trout in different dissolved solids concentrations occurred at 1022 mg litre −1 hardness.