Calculation of Intensity and Efficiency of Nutrition
115
per 1 sp. of larger animals (dadocerans, copepods, artemia nauplii). Then Cr =
WIRallgCcpm-l, where Ra measured radioactivity of labeled food material
expressed in the same way as the values of W.
For various calculations it is also necessary to estimate the carbon contents in the bodies of consumers (W). In small consumers it can be measured
as described above. The determine If' in larger animals, the alkaline
hydrolyzates of their bodies are used (see Sect. 3.4.2). Some 0.1-0.2ml of the
hydrolyzate is combusted by the wet combustion procedure.
3.4.2 Determination of Radioactivity in Consumers' Bodies (Ra)
The main problem in determining Ra in the consumers' bodies is to obtain a
homogenous liquid scintillation counting sample, which reduces quenching
and facilitates equalizing the counting conditions. Preparation of the counting
samples is quite simple when dealing with small animals like rotifers or
daphnia, which can easily be solubilized in the scintillation vials using standard solubilizers like NCS or Soluene, which are directly miscible with toluene
scintillation cocktails (Griffits and Caperon 1979). With larger animals, it is
more convenient first to solubilize or homogenize them separately in a beaker
of appropriate capacity. Then, portions of such a hydrolyzate (or homogenate),
containing almost equal amounts of dry material, are distributed into the scintillation vials. When working with small animals, after the feeding experiment
is finished, they are removed from the medium and the remains of labeled
food washed off, as described above (see Sect. 3.4.1). The animals of rotifer
or ciliate size are collected into small test tubes, which are then placed inside
the scintillation vials. Animals of the size of copepods or oligochaetes can be
placed directly into the scintillation vials. The excess of water in them is carefully extracted with a pipette (Fig. 3.3). The vials are placed into the thermostat at 40°C for drying. After the liquid evaporates, 0.1-0.5 ml of 20% NCS or
soluene solution in the methanol or in methoxyethanol is added, depending
on the mass of animals. The vials are capped and kept at 60°C for 10-15 h to
solubilize the animal's tissues. Into the vials, lOml of toluene-based scintillation cocktail is then added, and they are radioassayed. The radioactivity
thus measured is calculated per 10 3 sp. of the small animals or per 1 sp. of
larger animals like daphnia to obtain values of R a , 10 3 cpm Sp.-l or cpm Sp.-l,
respectively.
The samples with small to medium animals might be successfully solubilized also with the aid of a simple alkaline. For this, 0.1 to 0.5 ml of 5% KOH
is added into the vial, which is then kept (uncapped) at 90-95°C for several
hours. After cooling, 1 N RCl solution is added drop by drop into the vials until
gas (C02) formation in the sediment on the bottom ceases. The vials are kept
again at 60°C until the liquid evaporates. Then 0.5-1 ml of methanol or
methoxyethanol is added into them to dissolve the sediments on the bottom.
115
per 1 sp. of larger animals (dadocerans, copepods, artemia nauplii). Then Cr =
WIRallgCcpm-l, where Ra measured radioactivity of labeled food material
expressed in the same way as the values of W.
For various calculations it is also necessary to estimate the carbon contents in the bodies of consumers (W). In small consumers it can be measured
as described above. The determine If' in larger animals, the alkaline
hydrolyzates of their bodies are used (see Sect. 3.4.2). Some 0.1-0.2ml of the
hydrolyzate is combusted by the wet combustion procedure.
3.4.2 Determination of Radioactivity in Consumers' Bodies (Ra)
The main problem in determining Ra in the consumers' bodies is to obtain a
homogenous liquid scintillation counting sample, which reduces quenching
and facilitates equalizing the counting conditions. Preparation of the counting
samples is quite simple when dealing with small animals like rotifers or
daphnia, which can easily be solubilized in the scintillation vials using standard solubilizers like NCS or Soluene, which are directly miscible with toluene
scintillation cocktails (Griffits and Caperon 1979). With larger animals, it is
more convenient first to solubilize or homogenize them separately in a beaker
of appropriate capacity. Then, portions of such a hydrolyzate (or homogenate),
containing almost equal amounts of dry material, are distributed into the scintillation vials. When working with small animals, after the feeding experiment
is finished, they are removed from the medium and the remains of labeled
food washed off, as described above (see Sect. 3.4.1). The animals of rotifer
or ciliate size are collected into small test tubes, which are then placed inside
the scintillation vials. Animals of the size of copepods or oligochaetes can be
placed directly into the scintillation vials. The excess of water in them is carefully extracted with a pipette (Fig. 3.3). The vials are placed into the thermostat at 40°C for drying. After the liquid evaporates, 0.1-0.5 ml of 20% NCS or
soluene solution in the methanol or in methoxyethanol is added, depending
on the mass of animals. The vials are capped and kept at 60°C for 10-15 h to
solubilize the animal's tissues. Into the vials, lOml of toluene-based scintillation cocktail is then added, and they are radioassayed. The radioactivity
thus measured is calculated per 10 3 sp. of the small animals or per 1 sp. of
larger animals like daphnia to obtain values of R a , 10 3 cpm Sp.-l or cpm Sp.-l,
respectively.
The samples with small to medium animals might be successfully solubilized also with the aid of a simple alkaline. For this, 0.1 to 0.5 ml of 5% KOH
is added into the vial, which is then kept (uncapped) at 90-95°C for several
hours. After cooling, 1 N RCl solution is added drop by drop into the vials until
gas (C02) formation in the sediment on the bottom ceases. The vials are kept
again at 60°C until the liquid evaporates. Then 0.5-1 ml of methanol or
methoxyethanol is added into them to dissolve the sediments on the bottom.