8. THE REGULATION OF BREATHING
333
Hughes and Umezawa, 1968a,b). Using suitable siphons the expired
water can be collected for measurement. The method has the disadvantage of restricting the fish and placing a load on the muscles of
the branchial pump. A considerable effect of this type of system on the
oxygen consumption of Callionymus has been demonstrated by Hughes
and Knights (1968). Ventilation can be calculated from measurements
of the oxygen consumption of a fish if the oxygen content of the inspired
and expired water is also known. The method is suitable for work on
freely moving fish from which samples can be taken through buccal
and opercular catheters ( Saunders, 1962; Holeton and Randall, 1967a).
Inaccuracies will occur if the samples are not representative, and relatively small changes in oxygen concentration in considerable volumes
of water are not easily measured. A dye dilution technique has been
described by Millen et al. (1966). A bolus of dye is injected from a
syringe into the buccal or orobranchial cavity, and continuous sampling
from opercular or parabranchial chambers into a densitometer gives a
dye dilution curve. From the downslope of this curve the ventilation
volume can be calculated. For this technique to be accurate, the injection and sampling sites must be suitably located and the mixing of
the dye, once injected should be complete and preferably instantaneous.
Millen et al. (1966) achieved good mixing by implanting a stirrer in
the orobranchial cavity.
Utilization ( U ) is the ratio between oxygen extracted from the ventilation stream and oxygen contained in the inspired water, often expressed as a percentage:
where P is the partial pressure of gas, in I the inspired water, and E the
expired water. Its greatest use is probably in examining ventilation
and ventilation control because at known oxygen concentrations it relates oxygen consumption and ventilation in a direct way without involving the determination of any parameters in the circulatory system.
The relationship between ventilation volume and utilization is not a
simple one. This point is illustrated in Figs. 17 and 18 in which data
obtained by Holeton and Randall (1967b) and Stevens and Randall
(1967b) from the trout, Salmo gairdneri, are plotted. Thus the exercising
trout maintained a steady utilization of 10% and showed a progressively
increasing oxygen consumption as ventilation increased in air-saturated
water. The hypoxic trout also increased its ventilation over a similar
range, but it had a higher overall utilization falling to about 20% and
333
Hughes and Umezawa, 1968a,b). Using suitable siphons the expired
water can be collected for measurement. The method has the disadvantage of restricting the fish and placing a load on the muscles of
the branchial pump. A considerable effect of this type of system on the
oxygen consumption of Callionymus has been demonstrated by Hughes
and Knights (1968). Ventilation can be calculated from measurements
of the oxygen consumption of a fish if the oxygen content of the inspired
and expired water is also known. The method is suitable for work on
freely moving fish from which samples can be taken through buccal
and opercular catheters ( Saunders, 1962; Holeton and Randall, 1967a).
Inaccuracies will occur if the samples are not representative, and relatively small changes in oxygen concentration in considerable volumes
of water are not easily measured. A dye dilution technique has been
described by Millen et al. (1966). A bolus of dye is injected from a
syringe into the buccal or orobranchial cavity, and continuous sampling
from opercular or parabranchial chambers into a densitometer gives a
dye dilution curve. From the downslope of this curve the ventilation
volume can be calculated. For this technique to be accurate, the injection and sampling sites must be suitably located and the mixing of
the dye, once injected should be complete and preferably instantaneous.
Millen et al. (1966) achieved good mixing by implanting a stirrer in
the orobranchial cavity.
Utilization ( U ) is the ratio between oxygen extracted from the ventilation stream and oxygen contained in the inspired water, often expressed as a percentage:
where P is the partial pressure of gas, in I the inspired water, and E the
expired water. Its greatest use is probably in examining ventilation
and ventilation control because at known oxygen concentrations it relates oxygen consumption and ventilation in a direct way without involving the determination of any parameters in the circulatory system.
The relationship between ventilation volume and utilization is not a
simple one. This point is illustrated in Figs. 17 and 18 in which data
obtained by Holeton and Randall (1967b) and Stevens and Randall
(1967b) from the trout, Salmo gairdneri, are plotted. Thus the exercising
trout maintained a steady utilization of 10% and showed a progressively
increasing oxygen consumption as ventilation increased in air-saturated
water. The hypoxic trout also increased its ventilation over a similar
range, but it had a higher overall utilization falling to about 20% and