7. GAS EXCHANGE IN FISH
283
synchrony between a phase of the breathing cycle and the heart beat
occurs during hypoxia (Randall, 1966; Randall and Smith, 1967).
The eel often stops breathing for several seconds or breathes through
only one side of the gills; during these periods of reduced or no breathing the heart rate slows (Randall, 1962). A type of Cheyne-Stokes
breathing often occurs in quiet, inactive teleosts. As the breathing rate
oscillates heart rate also changes; the rate slows as breathing is
reduced or absent ( Labat et al., 1962; Peyraud and Serfaty, 1964). Thus
there appears to be a correlation between heart and breathing rate in
many fish under a variety of conditions, indicating some overall regulation of the ventilation-perfusion ratio.
V. THE EFFECTS OF VARIOUS PARAMETERS
ON GAS EXCHANGE
A. Temperature
The major effect of temperature on gas exchange is to change the
oxygen requirements of the fish. A change from 10" to 20°C increases
the standard oxygen uptake in the goldfish by 254% (Fry and Hart,
1948); the amount of oxygen in the water decreases by only 18% and
is offset by a decrease in viscosity of water and a more rapid rate of
diffusion of gases. Krogh's permeation coefficients increase by l%/ "C
(Table I ) . The fish must therefore adapt its respiratory system to meet
the increased oxygen demand as temperature rises.
There are a large number of studies demonstrating the effect of
temperature on the oxygen uptake of both resting and active fish (Brett,
1964; Fry, 1957). Thc increase in oxygen uptake with temperature is associated with an increase in cardiac output (Randall, 1968) and ventilation
volume (Davis, 1968). The peripheral resistance to blood flow decreases with increasing temperature ( Davis, 1968), reducing the amount
of work required of the heart to maintain a given cardiac output as the
temperature is raised.
The rate of oxygen transfer across the gills is limited either by the
cost of moving blood and water past the respiratory surface or by the
magnitude of the transfer factor of the gills for oxygen. Brett (1964)
showcd that maximum levels of sustained activity of salmon at temperatures above 15°C could be raised by supersaturating the water with
oxygen. These observations indicate that, under the conditions of his
experiments at least, either the cost of delivering oxygen to the gills or
the transfer factor of the gills for oxygen is limiting oxygen uptake.
283
synchrony between a phase of the breathing cycle and the heart beat
occurs during hypoxia (Randall, 1966; Randall and Smith, 1967).
The eel often stops breathing for several seconds or breathes through
only one side of the gills; during these periods of reduced or no breathing the heart rate slows (Randall, 1962). A type of Cheyne-Stokes
breathing often occurs in quiet, inactive teleosts. As the breathing rate
oscillates heart rate also changes; the rate slows as breathing is
reduced or absent ( Labat et al., 1962; Peyraud and Serfaty, 1964). Thus
there appears to be a correlation between heart and breathing rate in
many fish under a variety of conditions, indicating some overall regulation of the ventilation-perfusion ratio.
V. THE EFFECTS OF VARIOUS PARAMETERS
ON GAS EXCHANGE
A. Temperature
The major effect of temperature on gas exchange is to change the
oxygen requirements of the fish. A change from 10" to 20°C increases
the standard oxygen uptake in the goldfish by 254% (Fry and Hart,
1948); the amount of oxygen in the water decreases by only 18% and
is offset by a decrease in viscosity of water and a more rapid rate of
diffusion of gases. Krogh's permeation coefficients increase by l%/ "C
(Table I ) . The fish must therefore adapt its respiratory system to meet
the increased oxygen demand as temperature rises.
There are a large number of studies demonstrating the effect of
temperature on the oxygen uptake of both resting and active fish (Brett,
1964; Fry, 1957). Thc increase in oxygen uptake with temperature is associated with an increase in cardiac output (Randall, 1968) and ventilation
volume (Davis, 1968). The peripheral resistance to blood flow decreases with increasing temperature ( Davis, 1968), reducing the amount
of work required of the heart to maintain a given cardiac output as the
temperature is raised.
The rate of oxygen transfer across the gills is limited either by the
cost of moving blood and water past the respiratory surface or by the
magnitude of the transfer factor of the gills for oxygen. Brett (1964)
showcd that maximum levels of sustained activity of salmon at temperatures above 15°C could be raised by supersaturating the water with
oxygen. These observations indicate that, under the conditions of his
experiments at least, either the cost of delivering oxygen to the gills or
the transfer factor of the gills for oxygen is limiting oxygen uptake.