392
K JELL JOHANSEN
caused by incipient suffocation. On the other hand, there is little doubt
that many fishes living in severcly oxygen-deficient swamp water show
a clear chemotaxis for the more oxygen-rich surface layers of the swamp.
In fact, the existence of many fishes depends on frequent return to the
surface layers to satisfy respiratory needs (Carter and Bcadle, 1931b;
Johansen, 1968).
The apparent variance among fishes in their response to 0, gradients
does not extend to avoidance reactions to P,,, and pH gradients which
reportedly are common and much more acute (Shelford and Allee, 1913;
Hoglund, 1961 ) . Such reactions are presumably triggered by external
gustatory receptors (Scharrer et al., 1947). Some authors consider the
breathing responses to CO, change in fishes to be connected to chemoreceptors located in the gill region (Dijkstra, 1933; Powers and Clark,
1942; Jesse et al., 1967). Meanwhile, no experimental work has been
reported that conclusively identifies the location of and mechanism of
chemosensitive reflex control of breathing in fishes.
A consideration of these problems takes on special significance in
air-breathing fishes. From their practice of a dual mode of breathing
one will expect that air and aquatic breathing are both individually controlled and mutually coordinated.
E. Normal Breathing Behavior
The amplitude and frequency of both air and aquatic breathing in
air-breathing fishes are very labile. In fishes employing aquatic as well
as air breathing the frequency of branchial pumping generally exceeds
the frequency of air breathing. Commonly, the rate of branchial pumping is low just after an air breath, but it increases progressively before
the next air breath (Johansen and Lenfant, 1967, 1968). The contribution to gas exchange from air breathing evidently reduces the chemoreceptor drive to branchial breathing. Conversely, this drive will progressively increase with time after an air breath with a resultant higher
paced branchial pumping and finally evocation of another air breath.
The two types of breathing are apparently under a common or mutual
control. In many fishes, the rates of both branchial and air breathing
show a notable increase during swimming activity. Young specimens
of Neoceratodus change from sporadic air breaths during rest in aerated
water to a steady higher rate of air breathing during swimming (Grigg,
1965). Similarly, Polypterus senegalus and Amia calua, both of which
use the swim bladder for accessory air breathing, show an augmented
rate of branchial and air breathing with the onset of exercise (Magid,
K JELL JOHANSEN
caused by incipient suffocation. On the other hand, there is little doubt
that many fishes living in severcly oxygen-deficient swamp water show
a clear chemotaxis for the more oxygen-rich surface layers of the swamp.
In fact, the existence of many fishes depends on frequent return to the
surface layers to satisfy respiratory needs (Carter and Bcadle, 1931b;
Johansen, 1968).
The apparent variance among fishes in their response to 0, gradients
does not extend to avoidance reactions to P,,, and pH gradients which
reportedly are common and much more acute (Shelford and Allee, 1913;
Hoglund, 1961 ) . Such reactions are presumably triggered by external
gustatory receptors (Scharrer et al., 1947). Some authors consider the
breathing responses to CO, change in fishes to be connected to chemoreceptors located in the gill region (Dijkstra, 1933; Powers and Clark,
1942; Jesse et al., 1967). Meanwhile, no experimental work has been
reported that conclusively identifies the location of and mechanism of
chemosensitive reflex control of breathing in fishes.
A consideration of these problems takes on special significance in
air-breathing fishes. From their practice of a dual mode of breathing
one will expect that air and aquatic breathing are both individually controlled and mutually coordinated.
E. Normal Breathing Behavior
The amplitude and frequency of both air and aquatic breathing in
air-breathing fishes are very labile. In fishes employing aquatic as well
as air breathing the frequency of branchial pumping generally exceeds
the frequency of air breathing. Commonly, the rate of branchial pumping is low just after an air breath, but it increases progressively before
the next air breath (Johansen and Lenfant, 1967, 1968). The contribution to gas exchange from air breathing evidently reduces the chemoreceptor drive to branchial breathing. Conversely, this drive will progressively increase with time after an air breath with a resultant higher
paced branchial pumping and finally evocation of another air breath.
The two types of breathing are apparently under a common or mutual
control. In many fishes, the rates of both branchial and air breathing
show a notable increase during swimming activity. Young specimens
of Neoceratodus change from sporadic air breaths during rest in aerated
water to a steady higher rate of air breathing during swimming (Grigg,
1965). Similarly, Polypterus senegalus and Amia calua, both of which
use the swim bladder for accessory air breathing, show an augmented
rate of branchial and air breathing with the onset of exercise (Magid,