160
D. J. RANDALL
and freshwater species ) is approximately 3% body weight. Thorson
(1961) pointed out that the evolutionary trend in fish appeared to be toward smaller blood volumes, the significance of which is not clear.
Schiffman and Fromm (1959), Conte et al. (1963), and Ronald et d.
(1964) also reported blood volumes of approximately 3% body weight
in trout and cod. Most investigators have used methods developed for
determining blood volume in mammals. Many of these methods depend
on the injection of a dye and the measurement of its subsequent dilution
in the blood. It is important that the dye be evenly distributed throughout the vascular compartment before blood volume is determined. Most
investigators, in accord with mammalian practices, have allowed 30-40
min for equilibration of the dye. Smith (1966) found that Evans blue
(T-1824) was not evenly distributed in the blood of salmon until at
least an hour had elapsed, and reported blood volumes of 61% body
weight for a number of salmonids, approximately twice that previously
reported for any other teleost. This very slow mixing of the dye indicates the possibility of a slow turnover of blood in some parts of the
vascular system.
Violent bursts of swimming result in small increases in weight in
the trout. The concentrations of hemoglobin and plasma proteins
oscillate in phase with one another, indicating changes in the blood
water concentration during exercise. There is an initial hemodilution followed by a hemoconcentration as exercise continues (Stevens, 1968). The
weight gain and initial hemodilution could be the result of a net influx
of water into the blood across the gills, followed by an osmotic shift of
water into the muscles, causing the hemoconcentration. Exercise, or any
form of disturbance, increases blood catecholamine levels in salmonids
(Nakano and Tomlinson, 1967; Randall and Stevens, 1967), which in
turn alter the pattern of blood flow through the gills and increase the
rate of ion, water, and gas exchange (Baumgarten et al., 1969). Artificially raising the blood adrenaline levels in trout results in the fish
gaining weight. Thus any form of disturbance, which causes a rise in
blood catecholamine levels in freshwater fish, may cause a hemodilution
resulting from a net influx of water across the gills.
C. Blood Distribution
Circulation time can be calculated by dividing blood volume by
cardiac output per minute. If cardiac output is 25 ml/kg/min and
blood volume is 5% body weight, the calculated circulation time will be
2 min. Mott (1957) reported that blood took 5.6 k 1.9 sec to pass
D. J. RANDALL
and freshwater species ) is approximately 3% body weight. Thorson
(1961) pointed out that the evolutionary trend in fish appeared to be toward smaller blood volumes, the significance of which is not clear.
Schiffman and Fromm (1959), Conte et al. (1963), and Ronald et d.
(1964) also reported blood volumes of approximately 3% body weight
in trout and cod. Most investigators have used methods developed for
determining blood volume in mammals. Many of these methods depend
on the injection of a dye and the measurement of its subsequent dilution
in the blood. It is important that the dye be evenly distributed throughout the vascular compartment before blood volume is determined. Most
investigators, in accord with mammalian practices, have allowed 30-40
min for equilibration of the dye. Smith (1966) found that Evans blue
(T-1824) was not evenly distributed in the blood of salmon until at
least an hour had elapsed, and reported blood volumes of 61% body
weight for a number of salmonids, approximately twice that previously
reported for any other teleost. This very slow mixing of the dye indicates the possibility of a slow turnover of blood in some parts of the
vascular system.
Violent bursts of swimming result in small increases in weight in
the trout. The concentrations of hemoglobin and plasma proteins
oscillate in phase with one another, indicating changes in the blood
water concentration during exercise. There is an initial hemodilution followed by a hemoconcentration as exercise continues (Stevens, 1968). The
weight gain and initial hemodilution could be the result of a net influx
of water into the blood across the gills, followed by an osmotic shift of
water into the muscles, causing the hemoconcentration. Exercise, or any
form of disturbance, increases blood catecholamine levels in salmonids
(Nakano and Tomlinson, 1967; Randall and Stevens, 1967), which in
turn alter the pattern of blood flow through the gills and increase the
rate of ion, water, and gas exchange (Baumgarten et al., 1969). Artificially raising the blood adrenaline levels in trout results in the fish
gaining weight. Thus any form of disturbance, which causes a rise in
blood catecholamine levels in freshwater fish, may cause a hemodilution
resulting from a net influx of water across the gills.
C. Blood Distribution
Circulation time can be calculated by dividing blood volume by
cardiac output per minute. If cardiac output is 25 ml/kg/min and
blood volume is 5% body weight, the calculated circulation time will be
2 min. Mott (1957) reported that blood took 5.6 k 1.9 sec to pass