9. AIR BREATHING IN FISHES
387
30I" 25E
E
-
-
IO5 -
0 .
0
the lung disclose a near equilibrium indicating no role of the lung in gas
exchange. These samples were obtained between the sporadic breaths
for air which often fell more than one hour apart (Lenfant et al., 1966).
The two other species of lungfishes emphasize air breathing. In Lepidosiren paradoxa, blood from the pulmonary artery was only 40-50% saturated with O2 while that in the pulmonary vein was almost completely
saturated (Table IV). The difference in gas tensions between blood in
the dorsal aorta and the pulmonary artery demonstrates a partial selective passage of blood through the heart. This selective passage tends to
minimize recirculation of blood from the pulmonary vein back to the
lungs (Johansen and Lenfant, 1967; Lenfant et al., 1970).
In Protopterus aethiopicus passage of blood through the lung increases the 0, saturation more than 30% to exceed 90% of full saturation.
0 0 . Protopterus
A A
Neoceratodus
1
I
I
10
20
30
4 0
5 0
60
70
80
90 100
0, saturation (percent)
10 2030405060 70
80
90
100
Fig. 10. Nomogram comparing blood gas values in Neoceratodus and Protopterus
during undisturbed breathing in well-aerated water (values on stippled background )
and following air exposure. (Duration of air exposure in minutes indicated by numbers in parentheses.) PA, pulmonary artery; DA, dorsal aorta; and PV, pulmonary
vein. From Lenfant and Johansen ( 1968).