Figure 1.

An example of the changes in cardiac output in response to step increases in water velocity during a critical swimming speed test. The data (courtesy of Simonot 2006) are taken from triploid rainbow trout (Oncorhynchus mykiss; n=8; body mass=823 g; fork length, 37.4 cm; water temperature, 12–14°C). Cardiac output (mean±SEM) generally increases incrementally with swimming speed up to a maximum value and shows signs of a collapse at the critical swimming speed (U_crit). In addition, the continuous record clearly shows that at several of the intermediate swimming speeds cardiac output can initially overshoot the steady-state cardiac output. Also note that at the start of the swim test routine cardiac output was clearly elevated, as indicated by a lower steady-state cardiac output at the end of the 100 min recovery period following fatigue at U_crit.