4. THE CIRCULATORY SYSTEM
165
of arterial and venous blood; gases diffuse much more slowly, and so
there is probably only an insignificant exchange of gases across this rete.
Thermal and gaseous diffusion coefficients across the rete, however, have
not been measured.
The ability to thermoregulate varies. Large bluefin tuna appear to
have a greater capacity to thermoregulate than small fish. Skipjack and
yellowfin tuna can maintain an elevated muscle temperature, but it is
only a fixed value above ambient over a wide range of temperatures.
Large bluefin tuna can maintain a red muscle temperature of between
26" and 32"C, while the ambient temperature varies between 6" and
30°C. At low water temperatures the muscle is 20°C above ambient,
whereas at water temperatures of 30°C the muscle is only 2°C above
ambient. This implies regulation of muscle temperature, which could be
achieved by altering the functional size of the rete and/or by altering
blood 00w through the rete.
Lamnid sharks have a similar rete structure to bluefin tuna (Carey
and Teal, 1969b). Both groups can thermoregulate and are able to
swim swiftly, at a sustained speed, as a result of the extra power available from warm muscles. The bluefin tuna exists over a wide
range of temperatures and migrates long distances across several temperature zones, Carey and Teal (1969a) report an instance of a bluefin
tuna traveling from the Bahamas to Norway, a distance of 4200 nautical
miles, in less than 50 days. This is an excellent testimonial of the ability
of warm red muscles to maintain sustained swimming at high speed.
V. THE EFFECTS OF SOME SUBSTANCES
ON THE CIRCULATORY SYSTEM
When injected into, or otherwise applied to, the circulatory system of
fish, a large number of compounds are known to cause changes in blood
pressure and flow. The author has attempted to list the effects of a few
compounds on the cardiovascular system of fish; some of these responses
have already been discussed in preceding sections.
A. Acetylcholine
Acetylcholine increases the vascular resistance to flow through the
gills of teleosts (Keys and Bateman, 1932) directing blood away from
the secondary lamellae (Steen and Kruysse, 1964). The resistance to flow
165
of arterial and venous blood; gases diffuse much more slowly, and so
there is probably only an insignificant exchange of gases across this rete.
Thermal and gaseous diffusion coefficients across the rete, however, have
not been measured.
The ability to thermoregulate varies. Large bluefin tuna appear to
have a greater capacity to thermoregulate than small fish. Skipjack and
yellowfin tuna can maintain an elevated muscle temperature, but it is
only a fixed value above ambient over a wide range of temperatures.
Large bluefin tuna can maintain a red muscle temperature of between
26" and 32"C, while the ambient temperature varies between 6" and
30°C. At low water temperatures the muscle is 20°C above ambient,
whereas at water temperatures of 30°C the muscle is only 2°C above
ambient. This implies regulation of muscle temperature, which could be
achieved by altering the functional size of the rete and/or by altering
blood 00w through the rete.
Lamnid sharks have a similar rete structure to bluefin tuna (Carey
and Teal, 1969b). Both groups can thermoregulate and are able to
swim swiftly, at a sustained speed, as a result of the extra power available from warm muscles. The bluefin tuna exists over a wide
range of temperatures and migrates long distances across several temperature zones, Carey and Teal (1969a) report an instance of a bluefin
tuna traveling from the Bahamas to Norway, a distance of 4200 nautical
miles, in less than 50 days. This is an excellent testimonial of the ability
of warm red muscles to maintain sustained swimming at high speed.
V. THE EFFECTS OF SOME SUBSTANCES
ON THE CIRCULATORY SYSTEM
When injected into, or otherwise applied to, the circulatory system of
fish, a large number of compounds are known to cause changes in blood
pressure and flow. The author has attempted to list the effects of a few
compounds on the cardiovascular system of fish; some of these responses
have already been discussed in preceding sections.
A. Acetylcholine
Acetylcholine increases the vascular resistance to flow through the
gills of teleosts (Keys and Bateman, 1932) directing blood away from
the secondary lamellae (Steen and Kruysse, 1964). The resistance to flow