A STUDY OF THE CARDIOVASCULAR SYSTEM OF THE RAINBOW TROUT (SALMO GAIRDNERI) AT REST AND DURING SWIMMING EXERCISE

The effects of steady-state, aerobic swimming exercise upon blood volume and flow distribution in the rainbow trout (Salmo gairdneri) were examined. Isotopic Rubidium-86, and radiolabelled microspheres were injected into trout forced to swim against a current at 80% of their critical velocity (U(,crit)) in a Brett-type water tunnel respirometer. The results gathered from experiments using these radioactive tracers within the circulatory system of the trout indicated that blood flow during exercise was redistributed to favour working muscles, at the expense of diminished blood flow to those organs and tissues in the systemic circulation which could tolerate periods of transient hypoxia. Active hyperaemia in the skeletal muscle and vasoconstriction of the coeliacomesenteric artery, via adrenergic receptor mechanisms are proposed as the main sites of the control for blood volume and flow redistribution in the systemic circulation in trout during exercise.;The gills of these fish must be able to maintain adequate gas transfer in order to keep pace with the increased metabolic demands of the working muscles during exercise. An isolated, saline-perfused trout head preparation and a spontaneously ventilating, blood-perfused trout head preparation and a spontaneously ventilating, blood-perfused whole trout preparation were developed in order to study how increases in the pulsatility of input and increases in the cardiac output through these gills; cardiovascular alterations known to occur during exercise in vivo in these fish, affect fluid flow distribution through, and within the branchial vasculature, and gas exchange across the gills. Data from these preparations indicated that pulsatility of flow increased venolymphatic fluid drainage from within gill tissues, as well increasing the fluid flux/reflux across the branchial microvasculature. However, these changes in fluid distribution associated with increased pulse pressure did not significantly change the rate of gas transfer across the gills. Although gill vascular resistances to flow were very sensitive to alterations in pulse pressure and flow rate, only perfusion flow rate through the gills could cause significant changes in the rate of mass transfer of gases across the gills. The gills of trout therefore were found to be perfusion and not diffusion limited for gas transfer, under conditions which simulated those found at rest and during exercise, in vivo. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of school.) UMI...