Cardiovascular responses of winter flounder, Pseudopleuronectes americanus (Walbaum), to acute temperature increase

Abstract

Measurements of oxygen consumption rate, heart rate, total hemoglobin concentration, and arterial–venous blood pH, pressure, and oxygen tension and content were made on about 15 seasonally acclimatized winter flounder in flow-through respirometers at the seasonal mean temperatures of 5, 10, and 15 °C. These data along with calculated values of cardiac output and stroke volume were compared with similar measurements in winter flounder exposed to a 5 °C temperature increase over a 2-h period. To meet the significantly enhanced oxygen demand after the temperature increase, the primary cardiovascular adjustments changed from an increased arteriovenous (AV) O₂ content difference with no change in cardiac output at winter temperatures to an increased cardiac output and relatively unchanged AV O₂ difference at summer temperatures. Significantly increased heart rates also characterized the 5 °C increase at each of the seasonal regimes. Seasonal fluctuations in blood oxygen capacity may be influencing the observed changes in cardiovascular adjustment patterns to temperature increase.