304
C. SHELTON
be independent of the medium and related more directly to the nature of
the ventilating system. These considerations have led many workers to
conclude that the cost of breathing in aquatic organisms is very high
(Hughes and Shelton, 1962), although precise figures are not usually
available.
In man the total energy needed for breathing can be measured by
determining the overall oxygen consumption at different forced ventilation levels (Otis, 1964; Glauser et al., 1967). The cost in resting man
is about 2% of the overall oxygen consumption, although there is some
variation in different workers’ results. Pressure-volume measurements
have been used to determine the mechanical work of breathing (MilicEmili and Petit, 1960), and comparison of the two types of determination
gives efficiencies in respiratory musculature of 19-25%.
There are difficulties in persuading fish to ventilate their gills at
different levels by means which will not otherwise affect oxygen consumption. Conditions of carbon dioxide excess or oxygen lack will produce the necessary changes but it is known, for example, that oxygen
depletion ultimately limits uptake. Figures given by van Dam (1938),
who measured ventilation in eels and trout by enclosing their opercular
region in a chamber separated from the mouth, enable one to calculate
that the eel uses 10-12% and the trout 20% of its oxygen uptake for
the work of breathing. There are too few determinations to give any
degree of confidence in these calculations, added to which the fish, although fastened, may have been variably active. However, calculations
based on the results of other workers (Saunders, 1962; Holeton and
Randall, 196713) also give figures for metabolism of breathing muscles
between 10 and 15% of the resting oxygen uptake. Increased ventilation
certainly has a marked effect on oxygen uptake as Beamish (1964~)
demonstrated, He determined standard oxygen consumption in fish by
extrapolating the relationship between oxygen uptake and activity back
to zero activity. These extrapolations showed that the standard level
of oxygen uptake increased in goldfish, carp, and trout, as they breathed
more vigorously in lowered oxygen tensions (Fig. 16). Surprisingly,
carbon dioxide had no effect on standard oxygen consumption (Beamish,
1964d). Since ventilation volume was not measured, however, a more
quantitative relationship cannot be determined from these results.
Schumann and Piiper (1966) enclosed tench in the same type of
opercular chamber as used by van Dam in order to determine both
ventilation volume and oxygen uptake. Spontaneous changes in ventilation were used to determine the cost of breathing together with measurements of oxygen uptake during artificial ventilation of animals paralyzed
by succinylcholine. The results showed that 1843% of the total oxygen
C. SHELTON
be independent of the medium and related more directly to the nature of
the ventilating system. These considerations have led many workers to
conclude that the cost of breathing in aquatic organisms is very high
(Hughes and Shelton, 1962), although precise figures are not usually
available.
In man the total energy needed for breathing can be measured by
determining the overall oxygen consumption at different forced ventilation levels (Otis, 1964; Glauser et al., 1967). The cost in resting man
is about 2% of the overall oxygen consumption, although there is some
variation in different workers’ results. Pressure-volume measurements
have been used to determine the mechanical work of breathing (MilicEmili and Petit, 1960), and comparison of the two types of determination
gives efficiencies in respiratory musculature of 19-25%.
There are difficulties in persuading fish to ventilate their gills at
different levels by means which will not otherwise affect oxygen consumption. Conditions of carbon dioxide excess or oxygen lack will produce the necessary changes but it is known, for example, that oxygen
depletion ultimately limits uptake. Figures given by van Dam (1938),
who measured ventilation in eels and trout by enclosing their opercular
region in a chamber separated from the mouth, enable one to calculate
that the eel uses 10-12% and the trout 20% of its oxygen uptake for
the work of breathing. There are too few determinations to give any
degree of confidence in these calculations, added to which the fish, although fastened, may have been variably active. However, calculations
based on the results of other workers (Saunders, 1962; Holeton and
Randall, 196713) also give figures for metabolism of breathing muscles
between 10 and 15% of the resting oxygen uptake. Increased ventilation
certainly has a marked effect on oxygen uptake as Beamish (1964~)
demonstrated, He determined standard oxygen consumption in fish by
extrapolating the relationship between oxygen uptake and activity back
to zero activity. These extrapolations showed that the standard level
of oxygen uptake increased in goldfish, carp, and trout, as they breathed
more vigorously in lowered oxygen tensions (Fig. 16). Surprisingly,
carbon dioxide had no effect on standard oxygen consumption (Beamish,
1964d). Since ventilation volume was not measured, however, a more
quantitative relationship cannot be determined from these results.
Schumann and Piiper (1966) enclosed tench in the same type of
opercular chamber as used by van Dam in order to determine both
ventilation volume and oxygen uptake. Spontaneous changes in ventilation were used to determine the cost of breathing together with measurements of oxygen uptake during artificial ventilation of animals paralyzed
by succinylcholine. The results showed that 1843% of the total oxygen