Increased temperature tolerance of the air-breathing Asian swamp eel Monopterus albus after high-temperature acclimation is not explained by improved cardiorespiratory performance

摘要

This study investigated the hypothesis that in the Asian swamp eel Monopterus albus, an air-breathing fish from south-east Asia that uses the buccopharyngeal cavity for oxygen uptake, the upper critical temperature (T-U) is increased by acclimation to higher temperature, and that the increased T-U is associated with improved cardiovascular and respiratory function. Monopterus albus were therefore acclimated to 27 degrees C (current average) and 32 degrees C (current maximum temperature as well as projected average within 100-200 years), and both the effect of acclimation and acute temperature increments on cardiovascular and respiratory functions were investigated. Two weeks of heat acclimation increased upper tolerated temperature (T-U) by 2 degrees C from 369 +/- 01 degrees C to 389 +/- 01 degrees C (mean +/- s.e.). Oxygen uptake ((M) over dotO(2)) increased with acclimation temperature, accommodated by increases in both aerial and aquatic respiration. Overall, (M) over dotO(2) from air ((M) over dotO(2a)) was predominant, representing 85% in 27 degrees C acclimated fish and 80% in 32 degrees C acclimated fish. (M) over dotO(2) increased with acute increments in temperature and this increase was entirely accommodated by an increase in air-breathing frequency and (M) over dotO(2a). Monopterus albus failed to upregulate stroke volume; rather, cardiac output was maintained through increased heart rate with rising temperature. Overall, acclimation of M. albus to 32 degrees C did not improve its cardiovascular and respiratory performance at higher temperatures, and cardiovascular adaptations, therefore, do not appear to contribute to the observed increase in T-U.