The effects of hypersaline exposure on oxygen-affinity of the blood of the freshwater teleost Catostomus commersoni

After 10 days’ exposure to an environmental salinity of 300mosmol kg−1 NaCl, the freshwater stenohaline teleost Catostomus commersoni exhibited an increase in plasma osmolality and a reduction in plasma strong ion difference (SID). There were reductions in plasma pH (pHe), red blood cell (RBC) pH (pHi), plasma total CO2 and erythrocyte nucleoside triphosphate (NTP) concentration, and increases in mean erythrocyte volume and plasma catecholamine levels. Despite the acidosis, the in vitro haemoglobin oxygen-affinity of blood from saline-acclimated fish was not significantly different from that of control fish (held in fresh water) which had higher pHe and pHi values at the tensions used. In vitro adjustment of SID of blood from control fish to approximate that of the saline-acclimated fish by the addition of NaOH and HC1 significantly reduced pHe, pHi and the haemoglobin oxygen-affinity. Adjustment of the plasma osmolality of blood from control fish to values identical to those of the saline-acclimated fish by the addition of NaCl in vitro did not alter the haemoglobin oxygen-affinity. An increase in catecholamine concentration and a decrease in red blood cell N IP concentration in the saline-acclimated fish may have been compensatory mechanisms to maintain haemoglobin oxygen-affinity against acidosis-induced Bohr and Root effects during saline exposure.