The effects of temperature on the cardio-respiratory function of the neotropical fish Piaractus mesopotamicus

摘要

Piaractus mesopotamicus were acclimated to 35degreesC (group I) and 15degreesC (group II). In group I, temperature was decreased from 35degreesC to 15degreesC, followed by a return to 35degreesC, while in group II. temperature rose to 35degreesC and returned to 15degreesC. For each temperature, oxygen uptake ((V) over dot O-2). ventilatory parameters ((V) over dot (G), f(R), V-T, (V) over dot (G)/(V) over dot O-2), oxygen extraction (EO2) and ECGs were obtained. Group II developed a higher (V) over dot O-2 than group I. and the hysteresis presented by group I may characterize the attempt to reestablish the respiratory homeostasis. The V-T remained almost constant and the increases in (V) over dot (G), were achieved by larger increases in f(R). Group II presented significantly higher f(H) values between 30degreesC and 20degreesC when compared to the warm-acclimated group. Neither thermal acclimation nor changes in temperature affected the QRS and the T wave amplitudes, The increases of QRS and T wave durations. A(APD) and V-APD in group I suggest that low temperatures delayed the ionic diffusion within the sarcolemma and, thereby. the final depolarization and repolarization.