Measurements of Feeding, Food Assimilability, and Respiration
139
of the assimilability can be done with reasonable precision only with the use
of radiocarbon methodology (Edmondson and Winberg 1971).
The 14C technique to determine this parameter is based upon the estimation of elements of the balance equation (Q = A + F) in a single experiment
with the same group of animals (Sorokin 1968). The uniform labeling of the
food organisms (or of detritus material) in this case is obligatory. 'lhe group
of animals (or one large animal) is kept in the vessel with the labeled food, its
kind and concentration in water in the vessel being optimal for a given grazer.
The exposure of animals to the labeled food ends before the animals begin to
excrete feces containing the label. Then the animals are transferred into the
water containing unlabeled food, and the fate of the ingested labeled food is
sequenced using the sensitive radiocarbon label. The exact technique of these
balance experiments has been refined and tested many times with various
grazers during numerous research projects using this method (Sorokin and
Panov 1966; Sorokin 1968, 1991, 1993; Petipa et al. 1971; Sorokin and Giovanardi 1995). In Fig. 3.17, a general scheme is given which demonstrates the
sequence of experimental procedure during the study of nutrition balance of
fish larvae carried out using 14C as the label.
In conclusion, it should not be forgotten that in an investigation on the
nutrition of aquatic animals, the objectives of each study might be very different. In one series of studies, it might be sufficient to measure the relative
rates of nutrition or metabolism. In other studies, it is necessary to have
absolute values experessed in weight units. The procedure for estimation of
relative values is obviously much simpler than those of the absolute. For the
estimation of relative values Cr food analyses or Cq of respired CO2 are not
even obligatory. The values of relative radioactivity of the consumers' body
material can be sufficient in this case. The studies which require estimation of
the absolute rates of nutrition generally are restricted to measurements of a
single element of the balance equation rather than all parts of the equation.
For example, in order to study nutrition problems from the ecological aspects,
it is usually necessary to measure the relative intensity of food assimilation.
In this case, it is sufficient to measure only one element. namely, assimilation,
and calculate the food assimilability l. In other cases, it is necessary to determine only this assimilability index. Thus, the exact technique of the experiments must be selected in accordance with the objectives of the study; and the
simplest and most direct way might be practically used. The general schemes
for the estimation of nutrition using 14C as a label are shown in Figs 3,1 and
3.17.
3.6.2 Technique of the Balance Experiment
During the balance experiment, the following values have to be determined:
Re is the radioactivity of the consumed labeled food, cpm Sp.-I (see Sect. 3.5.2),
139
of the assimilability can be done with reasonable precision only with the use
of radiocarbon methodology (Edmondson and Winberg 1971).
The 14C technique to determine this parameter is based upon the estimation of elements of the balance equation (Q = A + F) in a single experiment
with the same group of animals (Sorokin 1968). The uniform labeling of the
food organisms (or of detritus material) in this case is obligatory. 'lhe group
of animals (or one large animal) is kept in the vessel with the labeled food, its
kind and concentration in water in the vessel being optimal for a given grazer.
The exposure of animals to the labeled food ends before the animals begin to
excrete feces containing the label. Then the animals are transferred into the
water containing unlabeled food, and the fate of the ingested labeled food is
sequenced using the sensitive radiocarbon label. The exact technique of these
balance experiments has been refined and tested many times with various
grazers during numerous research projects using this method (Sorokin and
Panov 1966; Sorokin 1968, 1991, 1993; Petipa et al. 1971; Sorokin and Giovanardi 1995). In Fig. 3.17, a general scheme is given which demonstrates the
sequence of experimental procedure during the study of nutrition balance of
fish larvae carried out using 14C as the label.
In conclusion, it should not be forgotten that in an investigation on the
nutrition of aquatic animals, the objectives of each study might be very different. In one series of studies, it might be sufficient to measure the relative
rates of nutrition or metabolism. In other studies, it is necessary to have
absolute values experessed in weight units. The procedure for estimation of
relative values is obviously much simpler than those of the absolute. For the
estimation of relative values Cr food analyses or Cq of respired CO2 are not
even obligatory. The values of relative radioactivity of the consumers' body
material can be sufficient in this case. The studies which require estimation of
the absolute rates of nutrition generally are restricted to measurements of a
single element of the balance equation rather than all parts of the equation.
For example, in order to study nutrition problems from the ecological aspects,
it is usually necessary to measure the relative intensity of food assimilation.
In this case, it is sufficient to measure only one element. namely, assimilation,
and calculate the food assimilability l. In other cases, it is necessary to determine only this assimilability index. Thus, the exact technique of the experiments must be selected in accordance with the objectives of the study; and the
simplest and most direct way might be practically used. The general schemes
for the estimation of nutrition using 14C as a label are shown in Figs 3,1 and
3.17.
3.6.2 Technique of the Balance Experiment
During the balance experiment, the following values have to be determined:
Re is the radioactivity of the consumed labeled food, cpm Sp.-I (see Sect. 3.5.2),