Despite the fact that it is a long time sinc e the methods of collection and quantitative estimatio n of protozoa were worked out data on the abundance of these animals in freshwaters are not very numerous. Nevertheless, Infusoria and Rhizopoda at high densities are widespread in the water and sediments of lakes and reservoirs. In order to find ou t the importance of infusoria as a food source for cyclopoids we carried out experimental investigations using C14. For this three species of cyclopoids, widely distributed in open regions of Rybinsk reservoir were selected: Cyclops vicinus, Mesocyclops oithonoides and Kesocyclops leuckarti. The data presented give evidence that the species investigated are able as predators to consume infusorian plankton arid bacteria in the form of flocs or small clumps of detritus

Monakov, A.V.

Sorokin, YU.I.

English

Aquatic Commons

Freshwater Biological Association 
FBA Translation (New Series) No. 143 
Title: The role of infusoria and bacteria as food for Cyclopoida in 
Rybinsk Reservoir. 
Author(s) Monakov, A.V. & Sorokin, Yu.I. 
Reference: Trudy Inst Biol .vnutr.Vod. 22(25), 37-42. (1971) 
Original language: Russian 
Date of publication of original: 1971 
Translator: I.M. Strachan 
Date of publication of translation: 
Number of pages of translation: 7 
FBA Translations are to be considered as "provisional". As a rule 
they have not been prepared by expert translators, nor have they 
been edited by the original authors. 
They are available from The Librarian, 
Freshwater Biological Association, 
The Ferry House, 
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AMBLESIDE. 
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England, at the current rate for xerox copying. 
F.B.A. Translation (New Series) No. 143 
The role of infusoria and bacteria as food for Cyclopoida 
in Rybinsk Reservoir. 
MONAKOV, A.V. & SOROKIN, Yu.I: 
Trudy Inst.Biol.vnutr.Vod. 22(25), 37-42 (1971) 
Translated by I.M. Strachan 
Despite the fact that it is a long time since the methods of 
collection and quantitative estimation of protozoa were worked out 
(Gaeviskaya, 1949) data on the abundance of these animals in freshwaters 
are not very numerous. Nevertheless, Infusoria and Rhizopoda at 
high densities are widespread in the water and sediments of lakes 
and reservoirs (Gourvich, 1961; Mordukhai-Boltovskaya, 1965; Shcherbakov, 
1967; Chorik, 1 9 6 9 ) . 
E.D.Kordukhai-Boltovskaya (1965) has shown that in Rybinsk 
reservoir the number of infusoria sometimes reaches a considerable 
value. Systematic observations on infusoria carried out by one of 
the authors in the Volga reach of Bybinsk reservoir have revealed two 
peaks in the number of these animals! in the 'dying off' period of 
diatoms (mid-June) and the 'dying off' period of blue-green algae 
(mid-August). Their biomass during this period reached 4-9 mg/l, and 
their numbers 500-1000 individuals per ml (Sorokin, 1970). Comparison 
of the seasonal dynamics of the populations of infusoria and their 
likely predators - cyclopoids - reveals a link between their numbers 
(fig.1). Maximum numbers of cyclopoids were observed at the end of 
June and the . end of August, directly following the maximum numbers of 
infusoria. These data indicate that infusoria in the present instance 
may have been the food source of cyclopoids, as the number of daphnids 
and rotifers in the period indicated was relatively low. 
In order to find out the importance of infusoria as a food 
source for cyclopoids we carried out experimental investigations 
using C14. 
For this we selected three species of cyclopoids, widely 
distributed in open regions of Rybinsk reservoir: Cyclops vicinus, 
Mesocyclops oithonoides and Kesocyclops leuckarti. 
2 
Cyclopoids were collected from the reservoir, transferred to 
the laboratory where they were identified to species, end placed in 
aquaria. The period of adaptation to experimental conditions war 
usually 24 hours, during which time the animals were fed with infusoria. 
The experimental animals were placed in small vessels containing 20-800ml 
depending on the particular experiment. Infusoria picked out from 
the reservoir water were cultured on bacterial food labelled with the 
carbon isotope C14. In the cultures the predominant infusoria 
measured 15 x 30 um. This was close to the mean size of infusoria 
found in the reservoir. The density of cyclopoids usually corresponded 
with their density in natural conditions. Experiments lasted 3-8 hours, 
at room temperature. At the end of an experiment the animals were 
rinsed in filtered water and transferred for half an hour to a vessel 
containing unlabelled food (rotifers, infusoria). 
In our work on the study of the nutrition of copepods we usually 
determined the radioactivity of animals in dried preparations. So, if 
a vessel contained 50 crustaceans, at the end of the experiment after 
fixation they were placed in five separate preparations (of ten individuals) 
in which their activity was determined with a correction for self-
absorption. Then the arithmetic mean was calculated, and sometimes the 
mean square deviation for the five cases. In the present work, at 
the end of an experiment the cyclopoids were removed from the experimental 
vessel with a pipette and from them a homogenate was prepared, which 
was distributed in a thin layer on an object-glass, dried, and its 
radioactivity determined under a meter. Knowing the radioactivity of 
the homogenate and the number of animals picked out, we were able to 
obtain the actual mean activity per crustacean. Naturally, in these 
calculations there could be room for systematic error, for example due 
to loss during preparation of the homogenate or fluctuation in feeding 
of each individual. In order to discover the size of such error, we 
performed the following experiment. In a vessel holding 250ml of water, 
containing radioactive infusoria, there were placed 200 individuals of 
Cyclops vicinus. After three hours the animals were divided into four 
lots (of 50 individuals) then from each lot a homogenate was made up. 
The radioactivity of the prepared homogenates. was found to be '78.0, 
90.4, 91.3 and 96.8. For these samples the maximum deviation from the 
mean value was only 11%. 
The quantity assimilated by cyclopoids from protozoa (Cy) without 
accounting for loss through respiration is calculated from the radioactivity 
of the animals (R) and the value of the specific activity of the food (Cr) 
3 
by the formula 
where T = length of experiment in hours (Sorokin, 1966). 
We have shown that the intensity of feeding is indicated by the index 
of assimilation (Cy /C) which represents the percentage ratio of the size 
of Cy to the total carbon content (C) of the experimental crustacean. 
Since c14 labelled infusoria, used as food, are difficult to separate 
from the labelled bacteria which serve as their food, there were often 
bacteria in the experimental vessels together with labelled infusoria. 
Is it not possible in such an instance for consumption of these bacteria 
by cyclopoids to affect the results of the experiment? We must answer 
this question in the negative as, firstly, in the experiments we used cultures 
of infusoria in which the numbers of bacteria were reduced by being consumed 
to below the margin of error. Secondly, it has been established previously 
that some species of cyclopoids, namely Mesocyclops leuckarti and 
Acanthocyclops viridis, are unable to utilise bacterioplankton (Monakov 
and Sorokin, 1960). 
In order to obtain additional proof we set up the corresponding 
experiment with Cyclops vicinus. Into five vessels (volume 200ml) of 
natural water, prefiltered through a No.3 filter, there were placed up to 
30 Cyclops individuals. To two of the vessels we added labelled bacteria 
so that their concentration in one case amounted to 4 million cells per ml, 
which was about twice as high as the number of bacteria in Rybinsk reservoir, 
and in another - 10 million cells per ml. Into the next two aquaria the 
same concentrations of bacteria were placed with the addition of a few 
protozoa. In the fifth vessel the cyclopoids were supplied with bacteria 
in the form of flocs. 
The results obtained (fig.2) show that bacterioplankton, even if its 
concentration is high, cannot serve as a food supply for Cyclops vicinus. 
With the inclusion of an additional link, which in our case was infusoria, 
the radioactivity of the predatory cyclopoias was much higher. A similar 
high level was shown for the radioactivity of the animals when feeding on 
bacterial flocs. 
The ability of C. vicinus to consume and assimilate bacteria in the 
form of flocs allows one to suppose that they can also feed on detritus, the 
4 
organic basis of which, as is known, is made up of bacteria and, probably, 
protozoa. This we have confirmed in an experiment, in which two species 
of cyclopoids were offered natural detritus with microflora labelled with 
c14. Detritus was collected from the bottom of a pond with a pipette and 
heated to a temperature of 50° in order to kill the protozoa. Later, 
labelled hydrolysed-protein was added to some of this. The detritus was 
left to stand for 2-3 days, during which time the natural microflora 
acquiried radioactive labelling by consuming radioactive hydrolysate. 
In view of the impossibility of determining Cr for detritus, it was 
assumed that the ratio of the radioactivity of the animals, feeding on 
labelled detritus, to their biomass would show the intensity of feeding. 
the crustacean Cypridopsis vidua, known to be a detritus feeder, was taken 
as a control. The experimental results (table 1) show that the cyclopoids 
are evidently able to feed on the microflora of detritus, although their 
intensity of feeding in this instance was three times lower than that of. 
Cypridopsis vidua. 
Finally, cyclopoids were" supplied with fresh infusorian plankton, the 
concentration of which approached that in nature. This shows that all the 
pelagic cyclopoids, and likewise the littoral form Eucyclops macruroides, 
are able to consume infusoria, dispersed in the water layer, at a concentration 
of approximately 50 individuals per ml. The index of assimilation for the 
cyclopoids was sufficiently high (table 2) and approaches the value obtained 
by us in an experiment investigating the diet of certain calanoids (Monakov 
and Sorokin, 1970). 
Thus the data presented give evidence for this, that the species 
investigated are able as predators to consume infusorian plankton arid 
bacteria in the form of flocs or small clumps of detritus. The first of 
these, as has been shown, has a high nutritive quality. The assimilability 
of this food, determined in a special equilibrium experiment on Cyclops 
vicinus, was shown to be a steady 80% (table 3). 
The question arises: what concentration of planktonic protozoa is a 
available to the cyclopoids? To answer this, the dependence of the feeding 
intensity of cyclopoids on infusorians, on the concentration of the latter, 
was determined. The experimental results are presented in table 4. From 
analysis it seems quite clear that stabilisation of the value of Cy/C is 
observed at certain concentrations of infusoria. For Cyclops vicinus and 
Mesocyclops oithonoides this ratio stopped increasing at concentrations of 
infusoria of 150-1000 indiv/ml, for Mesocyclops leuckarti - at even lower 
5 
concentrations of food. Probably at concentrations of infusoria lower 
than 150 individuals per ml cyclopoids experience a shortage of food. 
In the open regions of Rybinsk reservoir the numbers of infusoria 
in the summer months fluctuate between 30 and 150 indiv/ml, and in the 
littoral-up to 400 indiv/ml (Mordukhai-Boltovskaya, 1965). In the peak 
period their numbers were even higher - up to 1000 indiv/ml. These 
concentrations reach and even exceed the optimal levels, determined in 
the experiments. 
It is possible to surmise that in early spring, immediately after: 
the freeing of the reservoir (from ice), when the pelagic plankton is 
composed almost entirely of cyclopoids (Kordukhai-Boltovskoi and Monakov, 
1963; Luferova and Monakov, 1 9 6 6 ) , infusoria represent the main source of 
food for cyclopoids. According to the data of E'.D.Mordukhai-Boltovskaya 
( 1 9 6 5 ) , in this period the numbers of infusoria in the reservoir are 
usually very considerable. 
Literature (all in Russian) 
Gaevskaya, N.S. (1949) Protozoa. Life in freshwater of the USSR, vol II. 
Gourvich, V.V. (1961) Development of the microbenthic fauna and the demersal 
plankton in Kachovsk reservoir during the initial years of its 
existence. Author's abstract of Master dissertation, Kiev. 
Luferova, L.A. & A.V.Monakov ( 1 9 6 6 ) Zooplankton of Rybinsk reservoir in 
1956-1963. Trudy Inst.Biol.vnutr. Vod. 12(15) 
Monakov, A.V. & Yu.I.Sorokin (1960) Application of isotope method to the 
study of the feeding of cyclopoids and their naupliar stages on bacterial 
food. Izv.Acad.Nauk SSSR, ser.biol.,No.6. 
Monakov, A.V. & Yu.I.Sorokin (1971 ) Nutrition and food relationships of 
some calanoids. Trudy Inst.Biol.vnutr.Vod.,21(24) 
Mordukhai-Boltovskaya, E.D. ( 1 9 6 5 ) Some data on the biology of infusoria 
in Rybinsk reservoir. Trudy Inst.Biol.vnutr.Vod. 8(11),3-11. 
Mordukhai-Boltovskoi, P.D. & A.V.Konakov (1963) Distribution of zooplankton 
in Rybinsk reservoir in spring. Trudy Inst.Biol.vnutr.Vod. 6(9) 
Sorokin, Yu.I. ( 1 9 6 6 ) On the application of radioactive methods to the 
study of nutrition and food links of aquatic animals. Trudy Inst. 
Biol. vnutr. Vod. 12(15) 
Sorokin, Yu.I. (1971) Comparative estimation of the productivity of 
plankton in the shallow Volga reach of Rybinsk reservoir. 
Trudy Inst.Biol.vnutr.Vod. 21(24) 
6 
Chorik, F.P. (1969) Methods of collection and accurate quantitative 
estimation of free-living infusoria. Inf .Byull.Biol. vnutr. Vod. 3. 
Shcherbakov, A.P. ( 1 9 6 7 ) Lake Glubokoye. "Nauka" publ. 
Fig.1. Seasonal dynamics of the populations of 
infusoria(1) and cyclopids (2) in the Volga reach 
water of Rybinsk reservoir in 1967. 
Horiz.axis- months; vert.axis- left: density of 
cyclopids (indiv./l) -right: density of infusoria 
(indiv/ml). 
Fig.2. Consumption by cyclopids (Cyclops vicinus) of bacteria and infusoria. 
Vert. axis - radioactivity of food(?) (counts/min/indiv.) 
Horiz. axis (left to right) : bacteria (dispersed)- 4m cells/ml; sim.-
10 m cells/ml; 4 m cells/ml + infusoria; 10 m cells/ml + infusoria; 
bacteria (flocs). 
Table 1. Comparison of the intensity of feeding of cyclopids and an 
ostracod on the labelled microflora of detritus. 
species of 
crustacean 
number of 
crustaceans 
weight of 1 
crustacean 
(B),mg 
Radioactivity 
(R)of 1 indiv, 
counts/min. 
R 
B 
Cyclops vicinus 32 100 4.5 0.04 
Mesocyclops oithonoides 50 10 0.4 0.04 
50 30 3.7 | 0.12 
Species of 
cyclopid 
Number of 
crustaceans 
R,counts/ 
min/indiv. 
Cy(ug C/ 
day/indiv) 
cy/ * C 
Cyclops vicinus 23 564.1 1.5 15 
Mesocyclops leuckarti 25 184 .2 0.5 17 
M. oithonoides 43 157.8 0.4 40 
Eucyclops macruroides. 22 3 0 6 . 8 0 . 8 18 
Radioactivity taken up & assimilated from food, counts/50 indiv 
Assimilability 
A.100 Assimilated food Excretion Consumed food 
(A+F) Assimilated into body 
Respiratory 
loss 
Total 
(A) 
Solid Disp-
ersed 
Total 
(F) 
A + F ' % 
4050 6.10 466O 690 462 1152 5812 80.2 
7 
Table 2 . Assimilation of infusoria by cyclopids. 
Footnote. Duration of experiment - 8 hrs; Cr for infusoria - 0.92.10 -3 ug C. 
Table 3. Assimilability of infusoria for Cyclops vicinus. 
Footnote. Duration of experiment: consumption section - 20 min., 
assimilation section - 1 hr. Number of crustaceans - 50. 
Table 4. Dependence of the intensity of feeding of cyclopids on infusoria 
on the concentration of food. 
Footnote. Cr for infusoria - 1.62.10-3 ug c. Duration of experiment 
for C.vicinus - 1 hr.,for M.oithonoides & M.leuckarti - 3hr. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Notice 
 
 
Please note that these translations were produced to assist the scientific staff of the 
FBA (Freshwater Biological Association) in their research. These translations were 
done by scientific staff with relevant language skills and not by professional 
translators. 
 
 
 


The role of infusoria and bacteria as food for Cyclopoida in Rybinsk Reservoir [Translation from: Trudy Instituta Biologii Vnutrennykh Vodnany 22(25), 37-42, 1971]

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The role of infusoria and bacteria as food for Cyclopoida in Rybinsk Reservoir [Translation from: Trudy Instituta Biologii Vnutrennykh Vodnany 22(25), 37-42, 1971]

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