Effects of high intensity exercise training on cardiovascular function, oxygen uptake, internal oxygen transport and osmotic balance in chinook salmon (Oncorhynchus tshawytscha) during critical speed swimming

To examine cardiorespiratory plasticity, cardiovascular function, oxygen co nsumption, oxygen delivery and osmotic balance were measured at velocities up to critical swimming speed (U-crit) in seawater-adapted chinook salmon. We used two groups of fish. The control group had swum continuously for 4 m onths at a low intensity (0.5BLs(-1)) and the other was given a high-intens ity training regimen (a U-crit swim test on alternate days) over the same p eriod of time. Compared with available data for other salmonid species, the control group had a higher maximum oxygen consumption (<M>over dot(O2max); 244 mu mol O(2)min(-1)kg(-1)), cardiac output (<Q>over dot(max); 65 ml min (-1) kg(-1)) and blood oxygen content (Ca-O2; 15mlO(2)dl(-1)). Exercise tra ining caused a 50% increase in <M>over dot(O2max) without changing either U -crit or Ca-O2, even though there were small but significant increases in h ematocrit, hemoglobin concentration and relative ventricular mass. During s wimming, however, exercise-trained fish experienced a smaller decrease in b ody mass and muscle moisture, a smaller increase in plasma osmolality, and reduced venous oxygen stores compared with control fish. Consequently, exer cise training apparently diminished the osmo-respiratory compromise, but im proved oxygen extraction at the tissues. We conclude that the training-indu ced increase in <M>over dot(O2max) provided benefits to systems other than the locomotory system, such as osmoregulation, enabling trained fish to bet ter multitask physiological functions while swimming. Furthermore, because a good interspecific correlation exists between <M>over dot(O2max) and arte rial oxygen supply (<T>over dot(O2max); r(2)=0.99) among temperate fish spe cies, it is likely that Cao(2) and <Q>over dot(max) are principal loci for cardiorespiratory evolutionary adaptation but not for intraspecific cardior epiratory plasticity as revealed by high intensity exercise training.