Measurements of Feeding, Food Assimilability, and Respiration
141
previously described (see Sect. 3.4.2), the balance of the parameters listed
above will look as follows: Rc = Ra + Rc + R f .
Before the description of techniques for experimental determination of
these parameters, several general remarks must be made. The specific biological features of the animals studied, their physiological state, and their food
requirements in their ambiental conditions must be carefully considered
(Winberg 1964). The animal grazers for these experiments must be collected
from their natural populations. The animals thus collected could be used after
short period (12-24h) of their adaptation to the experimental conditions.
The water for the experiments is taken from the water basin. For most
of the experiments the water must be filtered through Millipore filters with
0.2-0.45-flm pores. During the various manipulations with the animals, such as
the transfer from one vessel to another, washing, etc., it is necessary to ensure
a uniform temperature of the water to avoid subjecting the animals to thermal
shock. It is necessary to avoid also their injury or drying. Devices for washing
and transferring animals are illustrated in Fig. 3.2.
As mentioned above, the balance experiments demand uniformly labeled
food sources; for preparation methods see Sect. 3.3. Then the Cr of thus
prepared food must be estimated as described above (see Sect. 3.4.1), and the
exact time of its digestion must be also determined experimentally (see Sect.
3.5.1).
The specific feature of the balance experiment is that the Re and Ra values
are estimated for the same group of animals and for the same portion of
labeled ingested food. This goal can be achieved in two different ways. One is
the separation of a whole group of grazers at the end of their incubation period
with the labeled food in two approximately equal subgroups. One of them is
transferred into the water with the unlabeled food to estimate the radioactivity of assimilated food material (Ra), while the other is used for the measurement of the radioactivity of consumed food Re. This method is applicable when
the grazers are relatively small. In this case, the Re value calculated per one
animal will be statistically safe to use as a part of the above balance (Re = Ra
+ Re + R f ); moreover, this could also be controlled by comparing the Rc value
thus estimated with those obtained in an alternative way - by the calculation
of the balance as a sum of components of the second part of above equation,
which must be equal to Re. This second method of choice becomes basic when
dealing with large animals, like young fish or clams, only a restricted number
of which can be used in the balance experiments, or when dealing with an
individual grazer specimen. For this occasion, the Re is calculated as the sum
of Re + Rm + R f , estimated for the same group of grazer animals.
The procedures to determine all these components also had been
described above (Sect. 3.5.2.4). Therefore, only some additional comment are
given below. The animals collected for the experiment have to be previously
adapted to the conditions of the experiment. To begin the experiment, they
must be placed into water prefiltered through the membrane filters to ensure
that no other source of food is present in it except the labeled food, otherwise
141
previously described (see Sect. 3.4.2), the balance of the parameters listed
above will look as follows: Rc = Ra + Rc + R f .
Before the description of techniques for experimental determination of
these parameters, several general remarks must be made. The specific biological features of the animals studied, their physiological state, and their food
requirements in their ambiental conditions must be carefully considered
(Winberg 1964). The animal grazers for these experiments must be collected
from their natural populations. The animals thus collected could be used after
short period (12-24h) of their adaptation to the experimental conditions.
The water for the experiments is taken from the water basin. For most
of the experiments the water must be filtered through Millipore filters with
0.2-0.45-flm pores. During the various manipulations with the animals, such as
the transfer from one vessel to another, washing, etc., it is necessary to ensure
a uniform temperature of the water to avoid subjecting the animals to thermal
shock. It is necessary to avoid also their injury or drying. Devices for washing
and transferring animals are illustrated in Fig. 3.2.
As mentioned above, the balance experiments demand uniformly labeled
food sources; for preparation methods see Sect. 3.3. Then the Cr of thus
prepared food must be estimated as described above (see Sect. 3.4.1), and the
exact time of its digestion must be also determined experimentally (see Sect.
3.5.1).
The specific feature of the balance experiment is that the Re and Ra values
are estimated for the same group of animals and for the same portion of
labeled ingested food. This goal can be achieved in two different ways. One is
the separation of a whole group of grazers at the end of their incubation period
with the labeled food in two approximately equal subgroups. One of them is
transferred into the water with the unlabeled food to estimate the radioactivity of assimilated food material (Ra), while the other is used for the measurement of the radioactivity of consumed food Re. This method is applicable when
the grazers are relatively small. In this case, the Re value calculated per one
animal will be statistically safe to use as a part of the above balance (Re = Ra
+ Re + R f ); moreover, this could also be controlled by comparing the Rc value
thus estimated with those obtained in an alternative way - by the calculation
of the balance as a sum of components of the second part of above equation,
which must be equal to Re. This second method of choice becomes basic when
dealing with large animals, like young fish or clams, only a restricted number
of which can be used in the balance experiments, or when dealing with an
individual grazer specimen. For this occasion, the Re is calculated as the sum
of Re + Rm + R f , estimated for the same group of grazer animals.
The procedures to determine all these components also had been
described above (Sect. 3.5.2.4). Therefore, only some additional comment are
given below. The animals collected for the experiment have to be previously
adapted to the conditions of the experiment. To begin the experiment, they
must be placed into water prefiltered through the membrane filters to ensure
that no other source of food is present in it except the labeled food, otherwise