112
Radioisotopic Methods for the Study of Nutrition in Aquatic Animals
3.4 Analyses of Basic Values Needed for the Calculation
of Intensity and Efficiency of Nutrition
Among the values required for the calculation of nutrition rates are: C inverse
specific radioactivity of the organic carbon of labeled food expressed as mg C
cpm- 1 ; Rc and Ra radioactivity of carbon in the consumers' bodies,
cpmsp.-l; Waverage content of organic carbon in the consumers' bodies, mg
CSp.-l; rl and r2 radioactivity of the portion of food organisms, cpmml- 1 ; rf
radioactivity of feces, cpmsp.-l; Cq inverse specific radioactivity of 14C02
respired by consumers, IlgCcpm-1.
3.4.1 Estimation of Cr
Estimation of C includes determining the absolute organic carbon (W)
content in a portion of labeled food, and its radioactivity (r) in the same
portion, that is in a fixed volume of suspension or a definite number of food
organisms in one portion of labeled food. The value of r must be measured
under conditions equal to those for counting radioactivity (Ra) in the bodies
of consumers after their feeding on this labeled food.
1. Measuring the radioactivity of labeled food (r)
The main stipulation for the estimation of r values, mentioned above, is the
similarity of counting conditions (e.g., counting efficiency, see Sect. 1.2.2)
during the estimation of both r and of Ra (radioactivity of carbon in consumers' bodies). By satisfying this stipUlation, it is possible to avoid all
difficulties with quench correction. It is only necessary to accept standard protocol for preparation of material of consumers' bodies for radioassay by liquid
scintillation counting. If such a standard procedure is tested and accepted, the
same protocol should be applied for r estimation, but using the unlabeled
animals instead of the labeled ones. In this case, the preparation procedure for
a scintillation counting sample should be as follows. The portions of labeled
food prepared for counting, e.g., a portion of diluted suspension of labeled
microalgae or bacteria (see below) or a definite amount of labeled animals
is placed into scintillation vials, which are kept in the thermostat at 40-50°C
to evaporate the water. To these are added equal amounts of unlabeled material from consumers' bodies, the quantity and state of which have been
decided by the protocol for radioassaying the body material of the labeled
animals. It can be a definite number of intact small to medium-sized animals
or a definite portion of the tissue hydrolyzate from the bodies of large animals
like clams or fish larvae. The portions should contain approximately the
same amounts of dry substance. The samples thus prepared are then treated
in exactly the same way as for measuring radioactivity in the consumers'
Radioisotopic Methods for the Study of Nutrition in Aquatic Animals
3.4 Analyses of Basic Values Needed for the Calculation
of Intensity and Efficiency of Nutrition
Among the values required for the calculation of nutrition rates are: C inverse
specific radioactivity of the organic carbon of labeled food expressed as mg C
cpm- 1 ; Rc and Ra radioactivity of carbon in the consumers' bodies,
cpmsp.-l; Waverage content of organic carbon in the consumers' bodies, mg
CSp.-l; rl and r2 radioactivity of the portion of food organisms, cpmml- 1 ; rf
radioactivity of feces, cpmsp.-l; Cq inverse specific radioactivity of 14C02
respired by consumers, IlgCcpm-1.
3.4.1 Estimation of Cr
Estimation of C includes determining the absolute organic carbon (W)
content in a portion of labeled food, and its radioactivity (r) in the same
portion, that is in a fixed volume of suspension or a definite number of food
organisms in one portion of labeled food. The value of r must be measured
under conditions equal to those for counting radioactivity (Ra) in the bodies
of consumers after their feeding on this labeled food.
1. Measuring the radioactivity of labeled food (r)
The main stipulation for the estimation of r values, mentioned above, is the
similarity of counting conditions (e.g., counting efficiency, see Sect. 1.2.2)
during the estimation of both r and of Ra (radioactivity of carbon in consumers' bodies). By satisfying this stipUlation, it is possible to avoid all
difficulties with quench correction. It is only necessary to accept standard protocol for preparation of material of consumers' bodies for radioassay by liquid
scintillation counting. If such a standard procedure is tested and accepted, the
same protocol should be applied for r estimation, but using the unlabeled
animals instead of the labeled ones. In this case, the preparation procedure for
a scintillation counting sample should be as follows. The portions of labeled
food prepared for counting, e.g., a portion of diluted suspension of labeled
microalgae or bacteria (see below) or a definite amount of labeled animals
is placed into scintillation vials, which are kept in the thermostat at 40-50°C
to evaporate the water. To these are added equal amounts of unlabeled material from consumers' bodies, the quantity and state of which have been
decided by the protocol for radioassaying the body material of the labeled
animals. It can be a definite number of intact small to medium-sized animals
or a definite portion of the tissue hydrolyzate from the bodies of large animals
like clams or fish larvae. The portions should contain approximately the
same amounts of dry substance. The samples thus prepared are then treated
in exactly the same way as for measuring radioactivity in the consumers'