4. THE CIRCULATORY SYSTEM
141
The heart of fish is composed of typical vertebrate cardiac muscle
fibers ( Yamauchi and Burnstock, 1968). The reported fiber diameters
are smaller than those of mammals and may account for the relatively
small number of intracellular potentials recorded from fish hearts. Jensen
(1965) reported atrial and ventricular fiber diameters in the hagfish
heart as 6.1 and 7.1 p , respectively. These are about half the size of
atrial and ventricular fibers in the dog.
B. Electrical Properties
Action potentials and electrocardiograms recorded from fish hearts
are similar to those recorded from other vertebrate hearts (Fig. 2).
Jensen (1965) recorded cardiac resting potentials of between 40 and 60
mV in the hagfish portal heart and in atrial and ventricular fibers in the
branchial heart of three species of hagfish, an elasmobranch, and two
marine teleosts. Other investigators have recorded resting potentials of
about 70 mV in atrial strips of the skate heart (Seyama and Irisawa,
1967), in the goldfish atrium and ventricle ( Kuriyama et al., 1960), and
in the trout ventricle (Fig. 2). Jaeger (1965) recorded somewhat
larger resting potentials from the atrium and ventricle of the roach,
Leuciscus rutilus L.
Initiation of the heartbeat usually occurs in the sinoatrial node (Mott,
1957), but the actual site and extent of the pacemaker region varies
from fish to fish. Jensen (1965) was able to record pacemaker potentials
from a large number of fibers in the branchial (systemic) and portal
heart of the hagfish. Those fibers having a pacemaker potential were
situated in both the atrium and the ventricle of the branchial heart. McWilliam (188.5) and Kisch (1948) have shown that in fish many regions
of the heart are capable of pacemaker activity.
The conduction velocities of the wave of excitation spreading out
from the pacemaker region are slower than in mammalian hearts
(Randall, 1968). The rate of spread of excitation varies in different
parts of the heart, and there are fast conducting pathways in the trout
ventricle, Salmo gairdneri, that transmit the wave of excitation rapidly
to the apex and cause it to contract before other parts of the ventricle
closer to the atrium and bulbus are excited (see Fig. 1).
The electrocardiogram has been recorded from a number of fish
(for references, see Randall, 1968; Mott, 1957) and consists of a P wave
followed by a QRS complex and a T wave (Fig. 2). Oets ( 1950) recorded a V wave which preceded the P wave and was associated with
a contraction of the sinus venosus in the eel. Chapman et al. (1963)
recorded a typical electrocardiogram from the hagfish; however, an-
141
The heart of fish is composed of typical vertebrate cardiac muscle
fibers ( Yamauchi and Burnstock, 1968). The reported fiber diameters
are smaller than those of mammals and may account for the relatively
small number of intracellular potentials recorded from fish hearts. Jensen
(1965) reported atrial and ventricular fiber diameters in the hagfish
heart as 6.1 and 7.1 p , respectively. These are about half the size of
atrial and ventricular fibers in the dog.
B. Electrical Properties
Action potentials and electrocardiograms recorded from fish hearts
are similar to those recorded from other vertebrate hearts (Fig. 2).
Jensen (1965) recorded cardiac resting potentials of between 40 and 60
mV in the hagfish portal heart and in atrial and ventricular fibers in the
branchial heart of three species of hagfish, an elasmobranch, and two
marine teleosts. Other investigators have recorded resting potentials of
about 70 mV in atrial strips of the skate heart (Seyama and Irisawa,
1967), in the goldfish atrium and ventricle ( Kuriyama et al., 1960), and
in the trout ventricle (Fig. 2). Jaeger (1965) recorded somewhat
larger resting potentials from the atrium and ventricle of the roach,
Leuciscus rutilus L.
Initiation of the heartbeat usually occurs in the sinoatrial node (Mott,
1957), but the actual site and extent of the pacemaker region varies
from fish to fish. Jensen (1965) was able to record pacemaker potentials
from a large number of fibers in the branchial (systemic) and portal
heart of the hagfish. Those fibers having a pacemaker potential were
situated in both the atrium and the ventricle of the branchial heart. McWilliam (188.5) and Kisch (1948) have shown that in fish many regions
of the heart are capable of pacemaker activity.
The conduction velocities of the wave of excitation spreading out
from the pacemaker region are slower than in mammalian hearts
(Randall, 1968). The rate of spread of excitation varies in different
parts of the heart, and there are fast conducting pathways in the trout
ventricle, Salmo gairdneri, that transmit the wave of excitation rapidly
to the apex and cause it to contract before other parts of the ventricle
closer to the atrium and bulbus are excited (see Fig. 1).
The electrocardiogram has been recorded from a number of fish
(for references, see Randall, 1968; Mott, 1957) and consists of a P wave
followed by a QRS complex and a T wave (Fig. 2). Oets ( 1950) recorded a V wave which preceded the P wave and was associated with
a contraction of the sinus venosus in the eel. Chapman et al. (1963)
recorded a typical electrocardiogram from the hagfish; however, an-