150
Radioisotopic Methods for the Study of Nutrition in Aquatic Animals
mination of the respiration rates in aquatic animals which breathe with atmospheric oxygen, such as the pulmonate gastropods. The radiocarbon method
avoids the above problems (Sorokin 1968). Its use enables such measurements
to be made in open aquaria in the presence of food and grass. This method
has been used to measure the respiration rate in gastropods and in fish larvae
(Sorokin and Panoy 1966; Tsiknon Lukanina and Sorokin 1966; Fcdorov and
Sorokin 1967).
The principle of it is as follows (see Fig. 3.17). The animals are fed with
labeled food with a high specific radioactivity for several days - up to 1 week
to be sure that the substances of metabolic pools in their bodies are uniformly
labeled. The level of their labeling should attain SO-10l0 3 cpmmg- 1 of wet
weight of their soft tissues. Before the experiment, the labeled animals are kept
for several hours in water without label. Then they are placed into small bottles
filled with water cleansed of TC02 by acidification and subsequent boiling.
Then its pH is returned to 8.2-8.S with S% KOH solution free of C0 2 - 3• The
normal content of dissolved oxygen is established in it by the blowing COr free
air. The animals are kept here for only 10 to 200 min. The water from this bottle
is immediately transferred into a closed flask to prevent contact with air. In this
water the inverse radioactivity (Cq) of CO2 respired at that moment by the
labeled animals is determined as described above (see Sect. 3.S.3). Then the
animals are placed for some hours into the open aquarium for the basic experiment. During our experiments with fish larvae, per volume of water in such an
aquarium of 1O-1S1 we placed 30 to SO labeled fish larvae 12-1S mm long for
2 to 4 h. It appeared to be quite sufficient to accurately measure the radioactivity of respired CO2 (rc) in 40-ml subsamples. To measure its rc, two to three
parallel 20-S0-ml subsamples of water are removed to measure the radioactivity of TC02 (see Sect. 3.4.4). Then the animals are collected again in a smallcapacity bottle (Fig. 3.17) and the Cq in the CO2 respired by them is measured
again. The absolute rate of respiration (Rm) is calculated using the equation:
(r ·c )
Rm = _c_q_ ~gCSp.-l h-1,
t
where rc is the mean radioactivity of respired CO2 measured in the water of
subsamples and calculated as cpmsp.-l; Cq is the mean inverse specific radioactivity of COrcarbon, respired by animals in small-capacity bottles when being
measured before and after their incubation in the large aquarium. The value
of rc is calculated accounting for the volume of subsample (Vc), total volume
of water in the large aquarium (Va) and number of animals in the experiment
r·V
(N): rc = -,--Q cpmsp.-l.
V·N ,
Both rj and Cq values are measured in BaC03 precipitates on the membrane filters (see Sect. 3.5.3). The above equation is valid without any quench
correction of both values if the weights of BaC03 precipitates are in both cases
less than S mg cm- 2 of the filter's area.
Radioisotopic Methods for the Study of Nutrition in Aquatic Animals
mination of the respiration rates in aquatic animals which breathe with atmospheric oxygen, such as the pulmonate gastropods. The radiocarbon method
avoids the above problems (Sorokin 1968). Its use enables such measurements
to be made in open aquaria in the presence of food and grass. This method
has been used to measure the respiration rate in gastropods and in fish larvae
(Sorokin and Panoy 1966; Tsiknon Lukanina and Sorokin 1966; Fcdorov and
Sorokin 1967).
The principle of it is as follows (see Fig. 3.17). The animals are fed with
labeled food with a high specific radioactivity for several days - up to 1 week
to be sure that the substances of metabolic pools in their bodies are uniformly
labeled. The level of their labeling should attain SO-10l0 3 cpmmg- 1 of wet
weight of their soft tissues. Before the experiment, the labeled animals are kept
for several hours in water without label. Then they are placed into small bottles
filled with water cleansed of TC02 by acidification and subsequent boiling.
Then its pH is returned to 8.2-8.S with S% KOH solution free of C0 2 - 3• The
normal content of dissolved oxygen is established in it by the blowing COr free
air. The animals are kept here for only 10 to 200 min. The water from this bottle
is immediately transferred into a closed flask to prevent contact with air. In this
water the inverse radioactivity (Cq) of CO2 respired at that moment by the
labeled animals is determined as described above (see Sect. 3.S.3). Then the
animals are placed for some hours into the open aquarium for the basic experiment. During our experiments with fish larvae, per volume of water in such an
aquarium of 1O-1S1 we placed 30 to SO labeled fish larvae 12-1S mm long for
2 to 4 h. It appeared to be quite sufficient to accurately measure the radioactivity of respired CO2 (rc) in 40-ml subsamples. To measure its rc, two to three
parallel 20-S0-ml subsamples of water are removed to measure the radioactivity of TC02 (see Sect. 3.4.4). Then the animals are collected again in a smallcapacity bottle (Fig. 3.17) and the Cq in the CO2 respired by them is measured
again. The absolute rate of respiration (Rm) is calculated using the equation:
(r ·c )
Rm = _c_q_ ~gCSp.-l h-1,
t
where rc is the mean radioactivity of respired CO2 measured in the water of
subsamples and calculated as cpmsp.-l; Cq is the mean inverse specific radioactivity of COrcarbon, respired by animals in small-capacity bottles when being
measured before and after their incubation in the large aquarium. The value
of rc is calculated accounting for the volume of subsample (Vc), total volume
of water in the large aquarium (Va) and number of animals in the experiment
r·V
(N): rc = -,--Q cpmsp.-l.
V·N ,
Both rj and Cq values are measured in BaC03 precipitates on the membrane filters (see Sect. 3.5.3). The above equation is valid without any quench
correction of both values if the weights of BaC03 precipitates are in both cases
less than S mg cm- 2 of the filter's area.