Use of 14C for Assessment of Nutritional Problems
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significantly facilitates experimental work, and thus enables the researcher to
obtain, within a short time, important quantitative information on the ecology,
physiology, and nutritional habits of the common hydrobiont species which
command the trophodynamics in a given aquatic ecosystem.
3.5.1 Assessing the Duration of Digestion
The time of digestion of a single portion of consumed food may be determined
in one of two ways:
1. A group of animals are fed with strongly labeled food for a very short
period (2-4min). They are then removed from the vessel with labeled food
and transferred to one containing nonlabeled food. Periodically, subsamples
from the vessel are taken and filtered to measure the radioactivity of the feces.
The time of digestion is equal to the period from the beginning of feeding the
animals with the nonlabeled food and the appearance of radioactivity in the
feces. An example of such an experiment is shown in Fig. 3.S.
2. A group of animals is fed with labeled food for 1 to 2 h, and then transferred into another vessel, or beaker, containing non labeled food, repeating
the transfers at intervals of 3-S min. The water remaining in the beakers after
removal of the animals is filtered through Millipore filters and the radioactivity of the feces measured. The time of digestion is equal to the time of disappearance of radioactivity from the feces. An example of such an experiment
is shown in Fig. 3.S, in which bream larvae were used (Fig. 3.4; Panov and
Sorokin 1962).
3.5.2 Assessing Comparative Rates of Food Ingestion and Assimilation
The comparative rates of food ingestion can be evaluated estimating Rc
radioactivity of ingested food. The values of Rc correspond to a relative ingestion rate of a given hydrobiont under given trophic conditions. In the same
way, the comparative rates of assimilation are indicated by Ra, radioactivity of
the food incorporated by animal consumers through digestion and assimilation, and also by the index of assimilation of labeled food (CalC). The latter
corresponds to the absolute amount of incorporated food (Ci) calculated per
24h and related to the body carbon of the hydrobiont. Actually, it shows what
percentage of the biomass of the consumer's body could be renewed by
feeding during 24 h under given trophic conditions.
1. Measuring the comparative rate of food ingestion (Re)
To measure Re values, the animals, selected in sufficient quantity for meaningful statistics (for example SO-100 copepods or 20-40 small fish larvae),
121
significantly facilitates experimental work, and thus enables the researcher to
obtain, within a short time, important quantitative information on the ecology,
physiology, and nutritional habits of the common hydrobiont species which
command the trophodynamics in a given aquatic ecosystem.
3.5.1 Assessing the Duration of Digestion
The time of digestion of a single portion of consumed food may be determined
in one of two ways:
1. A group of animals are fed with strongly labeled food for a very short
period (2-4min). They are then removed from the vessel with labeled food
and transferred to one containing nonlabeled food. Periodically, subsamples
from the vessel are taken and filtered to measure the radioactivity of the feces.
The time of digestion is equal to the period from the beginning of feeding the
animals with the nonlabeled food and the appearance of radioactivity in the
feces. An example of such an experiment is shown in Fig. 3.S.
2. A group of animals is fed with labeled food for 1 to 2 h, and then transferred into another vessel, or beaker, containing non labeled food, repeating
the transfers at intervals of 3-S min. The water remaining in the beakers after
removal of the animals is filtered through Millipore filters and the radioactivity of the feces measured. The time of digestion is equal to the time of disappearance of radioactivity from the feces. An example of such an experiment
is shown in Fig. 3.S, in which bream larvae were used (Fig. 3.4; Panov and
Sorokin 1962).
3.5.2 Assessing Comparative Rates of Food Ingestion and Assimilation
The comparative rates of food ingestion can be evaluated estimating Rc
radioactivity of ingested food. The values of Rc correspond to a relative ingestion rate of a given hydrobiont under given trophic conditions. In the same
way, the comparative rates of assimilation are indicated by Ra, radioactivity of
the food incorporated by animal consumers through digestion and assimilation, and also by the index of assimilation of labeled food (CalC). The latter
corresponds to the absolute amount of incorporated food (Ci) calculated per
24h and related to the body carbon of the hydrobiont. Actually, it shows what
percentage of the biomass of the consumer's body could be renewed by
feeding during 24 h under given trophic conditions.
1. Measuring the comparative rate of food ingestion (Re)
To measure Re values, the animals, selected in sufficient quantity for meaningful statistics (for example SO-100 copepods or 20-40 small fish larvae),