Use of 14C for Assessment of Nutritional Problems
123
After the experiment is finished, the animals are removed from the vessel
with labeled food, washed, and then transferred in the living state directly into
scintillation vials. Precautions must be taken to prevent losses of labeled food
consumed by animals by defecation caused by disturbance during the above
manipulations.
The radioactivity of the animals (Re) is then assayed by one of the methods
described above (see Sect. 3.4.2) and calculated per single animal (Re =
cpmsp.-l).
The values of Re as indices of the comparative rate of food ingestion
can be used to estimate parameters of ecology and physiology of nutrition,
like the dependence of the feeding rate on food concentration, localization of
feeding, impact of environmental conditions upon the physiological state of
hydrobionts, etc. (see below).
2. Estimation of comparative rate of food assimilation (Ra)
The experiments for Ra estimations are carried out in two steps. The first step
starts as described above for Re> but the animals are incubated with the labeled
food three to four times longer e.g., for a period equal to two to three digestion times. They are then washed free of the labeled food and transferred into
a vessel with unlabeled food, where they are kept some 1.5 times longer than
their digestion time (see above, Sect. 3.5.1). During this period, the animals
void their guts of the nonassimilated remains of food. After completing the
experiment, the animals are removed from the vessel, washed, and the radioactivity of their bodies material is radioassayed as described above (Sect. 3.4.2) .
without quench correction. The radioactivity values thus determined being calculated per sp. give the value of Ra in cpmsp.-l. It corresponds to a relative
amount of labeled food assimilated and incorporated into the consumer's body
at a given duration of feeding and under the given trophic conditions of the
experiment.
Some part of assimilated labeled organic matter will also be respired by
the consumers during the experiment and will escape measurement. Therefore, the Ra values are actually some 10 to 20% less than was originally assimilated. The relative size of these losses in a standard time protocol for the
experiments will be the same; the Ra values obtained for various trophic
conditions are reliable indices of comparative rates of assimilation, being a
comprehensive quantitative parameter for characterizing the comparative
intensity and efficiency of feeding of aquatic animals. The ratio Ral Re (on condition that both values are estimated within equal experimental conditions
with the same kind of labeled food) can be used with some correction to calculate the assimilability index of a given kind of food: I = (Ra 100 Kr)IRe, where
I is the index of food assimilability, %, and Kr the correction coefficient for
the respiratory losses of assimilated labeled food, the latter being roughly
assumed 1.2 for a small animals (1 mm size) and 1.1 for larger ones. More exact
values of I can be obtained by the balance experiments (see below), but even
without balance experiments, which are more complex and time-consuming,
123
After the experiment is finished, the animals are removed from the vessel
with labeled food, washed, and then transferred in the living state directly into
scintillation vials. Precautions must be taken to prevent losses of labeled food
consumed by animals by defecation caused by disturbance during the above
manipulations.
The radioactivity of the animals (Re) is then assayed by one of the methods
described above (see Sect. 3.4.2) and calculated per single animal (Re =
cpmsp.-l).
The values of Re as indices of the comparative rate of food ingestion
can be used to estimate parameters of ecology and physiology of nutrition,
like the dependence of the feeding rate on food concentration, localization of
feeding, impact of environmental conditions upon the physiological state of
hydrobionts, etc. (see below).
2. Estimation of comparative rate of food assimilation (Ra)
The experiments for Ra estimations are carried out in two steps. The first step
starts as described above for Re> but the animals are incubated with the labeled
food three to four times longer e.g., for a period equal to two to three digestion times. They are then washed free of the labeled food and transferred into
a vessel with unlabeled food, where they are kept some 1.5 times longer than
their digestion time (see above, Sect. 3.5.1). During this period, the animals
void their guts of the nonassimilated remains of food. After completing the
experiment, the animals are removed from the vessel, washed, and the radioactivity of their bodies material is radioassayed as described above (Sect. 3.4.2) .
without quench correction. The radioactivity values thus determined being calculated per sp. give the value of Ra in cpmsp.-l. It corresponds to a relative
amount of labeled food assimilated and incorporated into the consumer's body
at a given duration of feeding and under the given trophic conditions of the
experiment.
Some part of assimilated labeled organic matter will also be respired by
the consumers during the experiment and will escape measurement. Therefore, the Ra values are actually some 10 to 20% less than was originally assimilated. The relative size of these losses in a standard time protocol for the
experiments will be the same; the Ra values obtained for various trophic
conditions are reliable indices of comparative rates of assimilation, being a
comprehensive quantitative parameter for characterizing the comparative
intensity and efficiency of feeding of aquatic animals. The ratio Ral Re (on condition that both values are estimated within equal experimental conditions
with the same kind of labeled food) can be used with some correction to calculate the assimilability index of a given kind of food: I = (Ra 100 Kr)IRe, where
I is the index of food assimilability, %, and Kr the correction coefficient for
the respiratory losses of assimilated labeled food, the latter being roughly
assumed 1.2 for a small animals (1 mm size) and 1.1 for larger ones. More exact
values of I can be obtained by the balance experiments (see below), but even
without balance experiments, which are more complex and time-consuming,