8. THE REGULATION OF BREATHING
331
values. Beamish concluded that anaerobic respiration occurred in
reduced oxygen concentrations. He was able to show that fish which
were active to the same extent consumed less oxygen at lowered tensions
than they did in air-saturated water. Fish acclimated to low oxygen
tensions not only had lower standard rates of metabolism at those tensions but also showed reduced consumption for any level of activity
when compared with their fellows acclimated at air saturation values.
The acclimation appears to have some influence on the extent to which
a fish can indulge in anaerobic respiration. The accumulation of lactic
acid in the muscles and bloodstream of trout and sunfish during exercise
(Black et al., 1962) and hypoxia (Heath and Pritchard, 1965) and its
subsequent return to normal during a prolonged period of elevated
oxygen consumption are well established. Blazka ( 1958) produced
evidence for anaerobiosis during hypoxia in the crucian carp with no
oxygen debt or accumulation of lactate.
b. Ventilation Volume and Utilization. Although the factors outlined
above complicate the relationship between oxygen concentration, activity, and respiratory exchange, it is very likely that the gills and ventilating mechanism do tend to become limiting during respiratory dependence, The failure may result from deficiences in the measurement and
control systems or from physical limitations on the part of the respiratory
pump and exchanging surfaces. The augmented volume of water must
be sufficient not only to cope with the reduced oxygen content but
also to compensate for the increased work involved in ventilation and
the reduced utilization of oxygen in the ventilation stream. Indeed, it
has been argued (Hughes and Shelton, 1962) that the increased metabolic cost of breathing and the fall in utilization may together determine
the effective upper limit for gill ventilation rather than the capacity of
the pump itself. This suggestion was based on an unsubstantiated estimate of ventilation work and an extrapolation (shown by the dotted
line in Fig. 17) of van Dam’s data (1938) from a single trout recovering
from exercise in air-saturated water. The fall in utilization in this case
Fig. 16. The effect of changes in partial pressure of environmental oxygen on
standard and active oxygen consumption of fish: ( a ) trout, SaZueZinus fontinalC.
10°C. Active rates taken from ( A ) Basu (1959) and (0) Job (1955). Standard
rates taken from Beamish ( 1 9 6 4 ~ ) ; ( 0 ) values for fish acclimated to air saturation
and (0) fish acclimated to each of the partial pressures of oxygen used. The standard rates significantly higher at low oxygen tensions for those fish acclimated to air saturation. ( b ) Carp, Cyprinus carpio. 10°C. Active and standard rates taken from Beamish ( 1 9 6 4 ~ ) .
Symbols for standard rates as before; no significant difference exists in
this case between the two differently acclimated groups. Reproduced by permission
of the National Research Council of Canada from the Can. J . Zool. 42, 355-366.
331
values. Beamish concluded that anaerobic respiration occurred in
reduced oxygen concentrations. He was able to show that fish which
were active to the same extent consumed less oxygen at lowered tensions
than they did in air-saturated water. Fish acclimated to low oxygen
tensions not only had lower standard rates of metabolism at those tensions but also showed reduced consumption for any level of activity
when compared with their fellows acclimated at air saturation values.
The acclimation appears to have some influence on the extent to which
a fish can indulge in anaerobic respiration. The accumulation of lactic
acid in the muscles and bloodstream of trout and sunfish during exercise
(Black et al., 1962) and hypoxia (Heath and Pritchard, 1965) and its
subsequent return to normal during a prolonged period of elevated
oxygen consumption are well established. Blazka ( 1958) produced
evidence for anaerobiosis during hypoxia in the crucian carp with no
oxygen debt or accumulation of lactate.
b. Ventilation Volume and Utilization. Although the factors outlined
above complicate the relationship between oxygen concentration, activity, and respiratory exchange, it is very likely that the gills and ventilating mechanism do tend to become limiting during respiratory dependence, The failure may result from deficiences in the measurement and
control systems or from physical limitations on the part of the respiratory
pump and exchanging surfaces. The augmented volume of water must
be sufficient not only to cope with the reduced oxygen content but
also to compensate for the increased work involved in ventilation and
the reduced utilization of oxygen in the ventilation stream. Indeed, it
has been argued (Hughes and Shelton, 1962) that the increased metabolic cost of breathing and the fall in utilization may together determine
the effective upper limit for gill ventilation rather than the capacity of
the pump itself. This suggestion was based on an unsubstantiated estimate of ventilation work and an extrapolation (shown by the dotted
line in Fig. 17) of van Dam’s data (1938) from a single trout recovering
from exercise in air-saturated water. The fall in utilization in this case
Fig. 16. The effect of changes in partial pressure of environmental oxygen on
standard and active oxygen consumption of fish: ( a ) trout, SaZueZinus fontinalC.
10°C. Active rates taken from ( A ) Basu (1959) and (0) Job (1955). Standard
rates taken from Beamish ( 1 9 6 4 ~ ) ; ( 0 ) values for fish acclimated to air saturation
and (0) fish acclimated to each of the partial pressures of oxygen used. The standard rates significantly higher at low oxygen tensions for those fish acclimated to air saturation. ( b ) Carp, Cyprinus carpio. 10°C. Active and standard rates taken from Beamish ( 1 9 6 4 ~ ) .
Symbols for standard rates as before; no significant difference exists in
this case between the two differently acclimated groups. Reproduced by permission
of the National Research Council of Canada from the Can. J . Zool. 42, 355-366.