122
Radioisotopic Methods for the Study of Nutrition in Aquatic Animals
RI
100
1=23 min
50
1=29 min
........ _ -0-- - . j.([]:-:-: •••••• 0 ' .
o ....•
T.mln
o
10
15
20
25
30
35
40
Fig. 3.4. Estimation of digestion time (t) of a single portion offood by cladocerans
Bosmina longirostris (1) and Simocephalus vetulus (2), as measured by the time
required for the appearance of 14C-Iabeled feces
Ri
120
100
80
60
40
20
T.hours
0
0
0.5
1.5
2
2.5
3
3.5
Fig. 3.5. Estimation of digestion time (t) of ingested labeled food (Bosmina) by the
bream fish larvae as measured by recording the disappearance of labeled feces. R;
radioactivity of feces, l02cpm
should first be adapted to the conditions of the experiments by being kept for
some time in a vessel with labeled food. Then, they are transferred into a vessel
containing labeled food at a defined concentration. The relationship between
the volume of water in the vessel, the number of animals, and the concentration of food must be selected so that the food concentration does not
significantly change during the experiment. The duration of the experiment
must be one third less than the time required for digestion of a portion of the
ingested food. In experiments with mollusks and fish larvae, this is about 2 to
3 h; in experiments with Cladocera, 15-20min.