9. AIR BREATHING IN FISHES
379
aerated water of low COz content have blood which is adversely affected
by CO, and p H changes. Conversely, blood from fishes living in stagnant
swamps and creeks with 0,-deficient, C0,-rich water were distinctly less
sensitive and often even insensitive to CO, changes (Fig. 5 ) . For
instance, if Myelus setiger, normally living in well-aerated C0,-free
water, was transferred to a typical swamp habitat, its blood could never
be more than 40% saturated with oxygen because of the large Root and
Bohr shifts. It has been argued that the diminishing sensitivity to CO,
70
60
50
8
9
- 4c
-
-
C
a,
C
0 V
-
0" 3c
0
2c
IC
Xrus *
/
E l e c t r y
10
20
30
40
Pco, ( m m Hg)
Fig. 6. Comparison CO? dissociation curves from representative species of
air-breathing fishes. The black dots indicate the normal levels of arterial Pm,. Information selected from Lahiri et aI. (1968), Protopterus'; Johansen et al. (1968),
Electrophorus; Lenfant et al. ( 1970), S~mbranchus; Lenfant and Johansen ( 1968),
Lepidosiren and Protopterus; Johansen and Lenfant ( 1967 ), Lepidosiren (juvenile) ;
and Lenfant et al. (1966), Neocemtodus.