162
D. J. RANDALL
resistance and blood flow but only small changes in the volume of blood
in the vessels. Stevens measured only the instantaneous blood volume
in various tissues. The procedure he adopted did not enable him to
detect changes in blood flow. Very little is known about the relative
changes in flow to various organs during exercise in fish.
D. Skeletal Muscle Circulation
1. EXERCISE
There are two types of muscle fiber in the myotomes of fishes which
can be recognized by their color. Red or dark fibers form thin, lateral
superficial sheets just under the skin, white fibers make u p the rest of
the underlying muscle mass. The two types of muscle fiber form discrete
motor systems, receiving separate nervous innervation and having different enzymic distributions, mitochondria1 content, and fiber diameter.
White muscle is used in burst swimming of short duration, and cnc’rgy
is supplied by anaerobic glycolysis (Bone, 1966). During burst swimming there is a rapid depletion of muscle glycogen and a large lactate
production. The lactate diffuses slowly into the blood and up to 12 hr
postexercise recovery is necessary bcfore the low preexercise lactate
levels are restored (Stevens and Black, 1966). White muscle fatigues
rapidly, and the effects of burst activity on glycogen depletion and lactate
production are cumulative during the recovery period.
White myotomal muscle, constituting the major portion of the body,
is only used in burst activity of short duration. Fish, therefore, drag twothirds of their body around simply to effect escape reactions and various
other burst responses. The fish is streamlined and neutrally bouyant
and the cost of moving this volume of muscle is probably small,
especially if the maintainance and circulation of the muscle is minimized.
The sparse vascularization limits the oxygen supply and during activity
the muscle must operate anaerobically. The poor vascularization will
also contribute to the slow release of lactate from the muscle and so
minimize the effects of a massive lactate production on the rest of the
body.
Red myotomal muscle is used in sustained swimming and is almost
impossible to fatigue (Bone, 1966). Thcre are no changes in red muscle
glycogen content during activity, and energy is supplied by the oxidation
of fats. Thc blood volume and number of capillaries per unit weight
are three times that in white muscle (Stevens, 1968). Scombroids and
certain elasmobranchs, in addition to the superficial red muscles, have
D. J. RANDALL
resistance and blood flow but only small changes in the volume of blood
in the vessels. Stevens measured only the instantaneous blood volume
in various tissues. The procedure he adopted did not enable him to
detect changes in blood flow. Very little is known about the relative
changes in flow to various organs during exercise in fish.
D. Skeletal Muscle Circulation
1. EXERCISE
There are two types of muscle fiber in the myotomes of fishes which
can be recognized by their color. Red or dark fibers form thin, lateral
superficial sheets just under the skin, white fibers make u p the rest of
the underlying muscle mass. The two types of muscle fiber form discrete
motor systems, receiving separate nervous innervation and having different enzymic distributions, mitochondria1 content, and fiber diameter.
White muscle is used in burst swimming of short duration, and cnc’rgy
is supplied by anaerobic glycolysis (Bone, 1966). During burst swimming there is a rapid depletion of muscle glycogen and a large lactate
production. The lactate diffuses slowly into the blood and up to 12 hr
postexercise recovery is necessary bcfore the low preexercise lactate
levels are restored (Stevens and Black, 1966). White muscle fatigues
rapidly, and the effects of burst activity on glycogen depletion and lactate
production are cumulative during the recovery period.
White myotomal muscle, constituting the major portion of the body,
is only used in burst activity of short duration. Fish, therefore, drag twothirds of their body around simply to effect escape reactions and various
other burst responses. The fish is streamlined and neutrally bouyant
and the cost of moving this volume of muscle is probably small,
especially if the maintainance and circulation of the muscle is minimized.
The sparse vascularization limits the oxygen supply and during activity
the muscle must operate anaerobically. The poor vascularization will
also contribute to the slow release of lactate from the muscle and so
minimize the effects of a massive lactate production on the rest of the
body.
Red myotomal muscle is used in sustained swimming and is almost
impossible to fatigue (Bone, 1966). Thcre are no changes in red muscle
glycogen content during activity, and energy is supplied by the oxidation
of fats. Thc blood volume and number of capillaries per unit weight
are three times that in white muscle (Stevens, 1968). Scombroids and
certain elasmobranchs, in addition to the superficial red muscles, have