278
D. J. RANDALL
veloped. Here cutaneous respiration must be very significant ( Fry,
1957).
111. GAS EXCHANGE BETWEEN BLOOD AND TISSUES
There are very few direct measurements of tissue gas tensions in
fish. Haning and Thompson (1965) have recorded tissue P,,, levels of
9.2 mm Hg in the catfish. Gas tensions in venous blood are an indication
of tissue gas partial pressures; however, there is a gas gradient between
the tissues and blood, the magnitude of which is unknown. Oxygen and
carbon dioxide levels in mixed venous blood appear to be variable both
between species and within a single species (Garey, 1967; Holeton and
Randall, 1967b; Piiper and Baumgarten-Schumann, 1968a ) . Carbon dioxide tensions in trout venous blood are about 5 mm Hg, doubling during
activity. Values are generally lower for carp and dogfish. The Po, in
mixed venous blood is 3.2 mm Hg in the carp (Garey, 1967), 10 mm Hg
in the dogfish (Piiper and Baumgarten-Schumann, 1968a), and 19 mm
Hg in the trout (Stevens and Randall, 1967b). In the absence of direct
measurements one might assume that tissue P,,, is between 3 and 15 mm
Hg and Po? is between 1 and 15 mm Hg.
Almost nothing is known of the relative size of, and blood flow to,
the various capillary beds in the systemic circulation of fish. Red
myotomal muscle contains about 3 times as much blood and has 3 times
the number of capillaries per unit weight as white myotomal muscle
( Stevens, 1968a). White myotomal muscle, used during violent burst
responses, operates anaerobically. Po? levels are presumably much
lower, and P,, levels much higher, than those in red myotomal muscle,
which operates aerobically. Stevens ( 1968a) has estimated the volumc
distribution of blood to parts of the body of rainbow trout. He demonstrated that, except for a diminished spleen blood volume, the distribution of blood was unaffectcd by violent swimming. The retention of
lactic acid in white myotomal muscle for a consitlerablc period after
violent exercise or hypoxia (Leivestad et al., 1957) is enhanced by thc
small number of capillaries and may be aided by an ischemia during
and after excrcise or hypoxia.
Gas exchange across the retc mirabile and gas gland of the swim
bladder has been studied in dctail. These studies are reviewcd in the
chapter by Steen, this volume. Studics of other systemic capillary bcds
are sparse and poorly documentated.
Some teleosts have a rcte mirabile in the choroid layer of the eyc.
D. J. RANDALL
veloped. Here cutaneous respiration must be very significant ( Fry,
1957).
111. GAS EXCHANGE BETWEEN BLOOD AND TISSUES
There are very few direct measurements of tissue gas tensions in
fish. Haning and Thompson (1965) have recorded tissue P,,, levels of
9.2 mm Hg in the catfish. Gas tensions in venous blood are an indication
of tissue gas partial pressures; however, there is a gas gradient between
the tissues and blood, the magnitude of which is unknown. Oxygen and
carbon dioxide levels in mixed venous blood appear to be variable both
between species and within a single species (Garey, 1967; Holeton and
Randall, 1967b; Piiper and Baumgarten-Schumann, 1968a ) . Carbon dioxide tensions in trout venous blood are about 5 mm Hg, doubling during
activity. Values are generally lower for carp and dogfish. The Po, in
mixed venous blood is 3.2 mm Hg in the carp (Garey, 1967), 10 mm Hg
in the dogfish (Piiper and Baumgarten-Schumann, 1968a), and 19 mm
Hg in the trout (Stevens and Randall, 1967b). In the absence of direct
measurements one might assume that tissue P,,, is between 3 and 15 mm
Hg and Po? is between 1 and 15 mm Hg.
Almost nothing is known of the relative size of, and blood flow to,
the various capillary beds in the systemic circulation of fish. Red
myotomal muscle contains about 3 times as much blood and has 3 times
the number of capillaries per unit weight as white myotomal muscle
( Stevens, 1968a). White myotomal muscle, used during violent burst
responses, operates anaerobically. Po? levels are presumably much
lower, and P,, levels much higher, than those in red myotomal muscle,
which operates aerobically. Stevens ( 1968a) has estimated the volumc
distribution of blood to parts of the body of rainbow trout. He demonstrated that, except for a diminished spleen blood volume, the distribution of blood was unaffectcd by violent swimming. The retention of
lactic acid in white myotomal muscle for a consitlerablc period after
violent exercise or hypoxia (Leivestad et al., 1957) is enhanced by thc
small number of capillaries and may be aided by an ischemia during
and after excrcise or hypoxia.
Gas exchange across the retc mirabile and gas gland of the swim
bladder has been studied in dctail. These studies are reviewcd in the
chapter by Steen, this volume. Studics of other systemic capillary bcds
are sparse and poorly documentated.
Some teleosts have a rcte mirabile in the choroid layer of the eyc.