Preparation of Labeled Food
107
kind of food found to be optimal for a given consumer according to its food
spectrum (see above). The threshold concentration will be indicated at the corresponding curve by the point where it crosses the line corresponding to the
level of M expressed in the same carbon units as the values of A.
The respiration rate can also be measured by the 14C method. The advantage of this approach is the possibility of performing experiments in open
aquaria in the presence of food and weeds, and even having sand on the floor.
These conditions, which simulate those in situ, are very different from those
in a respirometer, where the animals are kept in a confined space, and cannot
respire normally. The 14C method to measure respiration rates is based on
determining the inverse specific radioactivity of carbon (Cr ) in the CO2
respired by labeled animals (Sorokin 1965).
An important trophic characteristic in filtering animals is their filtration
rate. Normally, this is estimated by determining the decrease in particulate
food concentration in the presence of filterers like Daphnia or clams. This is
much easier to do using 14C label as the indicator of the food concentration
(Rigler 1971a,b).
Below is described in more detail the preparation operations for the
14C-method, such as preparation of labeled food and determination of its
inverse specific radioactivity Cr, radioassay of animals' tissues, as also the
experimental techniques to estimate the above quantitative parameters that
characterize the nutrition of aquatic animals.
3.3 Preparation of Labeled Food
3.3.1 Labeling Algae and Plant Detritus
Microalgae are labeled via photosynthesis by growing them in a medium
containing 14C bicarbonate. For this, a usual culture medium can be applied
as used in algology. To preparate culture medium for freshwater algae,
natural lake water can be used after prefiltration. If necessary, the TC02
in it should be adjusted to less than 5-S mg C 1-1 by dilution with distilled
water. The common algae Chlorella or Scenedesmus grow well in the simple
buffer solution: NaH2P04 Ig; K2HP04 3g; NaN03 0.2g; MgS04 0.05g;
Ca(N03)2 0.01 g; Na2C03 0.05 g; FeCtz trace, tap water 50ml; distilled water to
11; pH ~ 7.S.
To grow marine algae, prefiltered seawater is used for culture media, in
which the Te02 content should be artificially decreased to ca. 5-10mgCl- 1 to
ensure appropriate inverse specific radioactivity Cr in the mature algae within
the range 0.3 to 0.5 x 10- 3 f.lg Ccpm- 1 without a large expenditure of the stock
solution of labeled 14C-carbonate and without inducing too high a radioactivity in the culture vessels. To decrease the TC02 content in seawater, it is first
acidified by addition of 2 mll- 1 of conc. HCl, and then bubbled with air for half
107
kind of food found to be optimal for a given consumer according to its food
spectrum (see above). The threshold concentration will be indicated at the corresponding curve by the point where it crosses the line corresponding to the
level of M expressed in the same carbon units as the values of A.
The respiration rate can also be measured by the 14C method. The advantage of this approach is the possibility of performing experiments in open
aquaria in the presence of food and weeds, and even having sand on the floor.
These conditions, which simulate those in situ, are very different from those
in a respirometer, where the animals are kept in a confined space, and cannot
respire normally. The 14C method to measure respiration rates is based on
determining the inverse specific radioactivity of carbon (Cr ) in the CO2
respired by labeled animals (Sorokin 1965).
An important trophic characteristic in filtering animals is their filtration
rate. Normally, this is estimated by determining the decrease in particulate
food concentration in the presence of filterers like Daphnia or clams. This is
much easier to do using 14C label as the indicator of the food concentration
(Rigler 1971a,b).
Below is described in more detail the preparation operations for the
14C-method, such as preparation of labeled food and determination of its
inverse specific radioactivity Cr, radioassay of animals' tissues, as also the
experimental techniques to estimate the above quantitative parameters that
characterize the nutrition of aquatic animals.
3.3 Preparation of Labeled Food
3.3.1 Labeling Algae and Plant Detritus
Microalgae are labeled via photosynthesis by growing them in a medium
containing 14C bicarbonate. For this, a usual culture medium can be applied
as used in algology. To preparate culture medium for freshwater algae,
natural lake water can be used after prefiltration. If necessary, the TC02
in it should be adjusted to less than 5-S mg C 1-1 by dilution with distilled
water. The common algae Chlorella or Scenedesmus grow well in the simple
buffer solution: NaH2P04 Ig; K2HP04 3g; NaN03 0.2g; MgS04 0.05g;
Ca(N03)2 0.01 g; Na2C03 0.05 g; FeCtz trace, tap water 50ml; distilled water to
11; pH ~ 7.S.
To grow marine algae, prefiltered seawater is used for culture media, in
which the Te02 content should be artificially decreased to ca. 5-10mgCl- 1 to
ensure appropriate inverse specific radioactivity Cr in the mature algae within
the range 0.3 to 0.5 x 10- 3 f.lg Ccpm- 1 without a large expenditure of the stock
solution of labeled 14C-carbonate and without inducing too high a radioactivity in the culture vessels. To decrease the TC02 content in seawater, it is first
acidified by addition of 2 mll- 1 of conc. HCl, and then bubbled with air for half