2 Seasonal changes of food of vendace from the Maróz lake

2 Seasonal changes of food of vendace from the Maróz lake

ZESZYTY NAUKOWE UNIWERSYTETU SZCZECIŃSKIEGO
NR 676
ACTA BIOLOGICA 18
2011
URSZULA SZYMAŃSKA*1
SEASONAL CHANGES OF FOOD
OF VENDACE FROM THE MARÓZ LAKE AGAINST
A BACKGROUND OF THE FOOD RESOURCES**2
Abstract
Studies on diet of vendace from the Maróz Lake were carried out to determine seasonal changes in food composition in relation to changes of zooplankton food resources
in the environment. Fish samples, were collected once a month from April to November
in the years 1994–1996. A total of 409 alimentary tracts were analyzed. Simultaneously, crustacean zooplankton samples were collected to assess food abundance. The
occurrence of Cladocera and Copepoda in zooplankton samples from the Maróz Lake.
Food composition in the gut of vendace did not correspond with zooplankton abundance in the water. Due to considerable oxygen deficiency in the Maróz Lake (recorded
in water layer 4 m below the surface), especially in June, it may be presumed that sublittoral or even littoral was the bottom zone accessible for vendace, what, in turn, seems
to be indicated by the presence of detritus, algae and macrophytes debris in food of the
considered fish species.
Keywords: vendace, food composition, zooplankton, Maróz Lake
*
Faculty of Law and Administration, Laboratory of Law Protection of the Environment, Chair
of Crime Detection and Forensic Medicine, University of Warmia and Mazury in Olsztyn, urszula.
[email protected].
1
2 **
The study was carried out within the framework of the grant from KBN no. 506E041 10,
Interakcje w zespołach ryb na podstawie odłowów gospodarczych i ekologii odżywiania się
wybranych gatunków w jeziorach sielawowych, Urszula Szymańska.
18
Urszula Szymańska
Introduction
The vendace (Coregonus albula (L.)) are generally found in clean, cold and
oxygen-rich water of lakes (Dembiński 1971, Bernatowicz et al. 1975, Brylińska
et al. 2000, Winfield et al. 2004). This species is an obligatory zooplankton feeder,
evolutionarily adapted to feeding exclusively on crustacean zooplankton. The
prey is easily visible in clean water and the reaction distance is greater, so food
intake is more efficient under such conditions (O’Brien 1987). The above water
parameters are typical of oligotrophic and mesotrophic lakes, but the deterioration
of their trophic quality limits the natural occurrence of the vendace, mainly due
to the silting up of breeding grounds and low reproduction efficiency (Wilkońska
& Żuromska 1982, Wilkońska 1992).
Rapid changes in the living conditions of fish are usually followed by
adaptation or elimination of a given species from the ecosystem. In the case
of vendace this includes the inability to reproduce naturally in many lakes.
The focus of the present study was to determine seasonal changes of food
of vendace from the Maróz Lake and compare their diet to the food resources
available.
Materials and Methods
Vendace were collected from years 1994–1996, monthly, from April
to November, from fish caught in Lake Maróz by vendace gill nets (bar of mesh
# 22–28 mm) and a seine with bag (bar of mesh at wings #30 mm, bar of mesh
at bag #22 mm, bar of mesh at codend #20 mm). A seine was used in April only,
not to disturb bottom deposits and due to frequent oxygen deficits in the summer.
The fish taken for analyses were measured to 0,1 cm (Longitudo corporis – l.c.)
and weighed to 0,02 g immediately after capture. Their alimentary tracts were
preserved in 4% formalin. The contents of 409 digestive tracts of the vendace
were analyzed (Table 1).
19
Seasonal changes of food of vendace...
Table 1. Characteristics of the vendace taken for analyses from Lake Maróz in the years
1994–1996
Month
April
May
June
August
September
Number of fish
collected for
analyses
(specimes)
16
67
68
23
40
46
149
409
including
fish with full
digestive tracts
(specimes)
(%)
14
87.50
62
92.54
49
72.06
20
86.96
39
97.50
45
97.83
108
72.48
337
82.40
Mean length
Lc.
(cm)
16.9
17.8
18.0
19.0
18.4
18.4
18.0
Length range
(cm) 15.0–21.0 16.0–20.5 15.8–21.0 17.4–21.3
15.9–20.2
October November
15.5–22.5 15.4–21.3
total
18.7
15.0–
22.5
SD
1.8
1.0
1.0
1.0
1.0
1.6
1.2
1.2
Mean weight
(g)
58.00
68.40
76.01
79.89
77.60
77.47
70.63
71.29
Weight range
(g)
36.00–
103.00
49.90–
99.32
46.42–
117.36
62.78–
109.06
56.24–
106.64
42.20–
125.54
40.16–
114.14
36.00–
125.54
SD
18.84
11.44
14.18
11.86
12.15
20.90
14.35
15.12
The contents of the digestive tracts were weighed accurate to 0,02 g wet
weight (balance model WPE 600), and examined under a stereoscopic microscope
(at a magnification of 0.63x, 1x, 1.63x, 4x) in order to class, by the item into
a specific food category. The food components were divided into countable,
expressed as numerical and weight shares, e.g. zooplankton crustaceans
(copepods – Copepoda, cladocerans – Cladocera, rotifers – Rotifera, insect larvae
and pupae, fish eggs, ostracods – Ostracoda, aselli – Asellus aquaticus (L.), water
mites – Hydracarina), and uncountable, expressed as a weight share only, e.g.
detritus, algae and macrophytes. The weight proportion of these components
was determined by the point method (Pliszka 1956, Terlecki et al. 1977, Terlecki
1993). The weight of uncountable components was estimated using the formula
proposed by Martyniak (1993):
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Urszula Szymańska
Ms
Ps ˜ M
P
P – 100% of the area occupied by food components
M – weight of the contents of a single digestive tract
Ps – % of estimated area P occupied by food component s
Ms – weight of a food component.
The countable components were determined by the method developed by
Starmach (1955), using a BIOLAR microscope (at a magnification of 5x, 10x,
20x). They were identified to genus or, if possible, to species. The size of specimens
representing particular taxa, found most frequently in the food, was estimated
accurate to 0.05 mm. This provided a basis for reconstructing weight, using weight
functions and standards developed by Morduchaj-Boltowskoj (1954), Starmach
(1955), Pecen (1965), Lebedeva & Kozlowa (1969) and Terlecki (1979).
The results were analyzed by universally accepted methods taking into
account number share (NS), weight share (WR), occurence frequency (OF) and
relative importance index (RI), as described by Hyslop (1980).
Data on the abundance of net crustacean zooplankton in the fishing zones
were also gathered. Zooplankton samples were taken with a 5 dm3 bucket
(TOŃ 2). Sixty liter samples were concentrated to a volume of approx. 100 ml
using a plankton net no. 30, and preserved in 4% formalin. A total of 22 samples
were collected and analyzed. The taxonomic status and weight of zooplankton
components were determined as described in the case of countable food
ingredients. The taxonomic status of zooplanktonic organisms was defined using
the keys developed by Manujłowa (1964), Kiefer & Fryer (1978) and Edmondson
(1971).
Hydrobiological and fishing characteristics of Lake Maróz
Lake Maróz belongs to the complex of Olsztyn Lakeland lakes, in the
Łyna-Pregoła River basin, latitude 53°31.5’, longitude 20°24.6’, altitude 43 m
above sea level (Korycki 1963, Ciepielewski 1971). The lake is surrounded by
a pine and mixed forest, as well as numerous recreational centers and camping
sites, the majority of which have no plumbing systems. Wastewater is discharged
directly into the lake, especially in the summer. Lake Maróz is a post-glacial,
ribbon lake. The Marózka River that flows through this lake carries domestic
21
Seasonal changes of food of vendace...
sewage from nearby villages and a pig farm. The morphometric parameters
of Lake Maróz are given in Table 2.
Table 2. Morphometric parameters of Lake Maróz (based on Korycki 1963)
Name and symbol
Water table surface (P)
Unit of measure
Value
ha
332.5
Maximum length (D)
m
5580
Maximum width (S)
m
1200
Shoreline length (L)
m
18000
Depth (G)
– maximum
– mean V/P
m
m
41
11,9
ths m3
39566.2
Lake volume (V)
The sandy-gravelly bed of the lake has silted up, which decreased the area of the
breeding grounds of fish of the genus Coregonus (Wilkońska & Żuromska 1982,
Wilkońska et al. 1994). According to the typology proposed by Stangenberg
(Ciepielewski 1971), Lake Maróz is an eutrophic water body, and according to
Szczerbowski et al. (1993) it should be classified as a vendace-type lake, due
to the specific species composition of fish (vendace, common whitefish, smelt,
bleak, roach, pike, perch and other).
Results and Discussion
Zooplankton in Lake Maróz are comprised of Cladocera and Copepoda.
Means obtained for 1994–1996 confirmed the domination of Cladocera (69.65%)
(Figure 1, Annex 1). Species not reported from this lake before but were found
in current study include: Chydorus sphaericus (O.F. Muller) and Bosmina
longirostris (O.F. Muller) (Annex 1). Karabin (1985) classified these species
as indicators of fertile waters, so their presence in Lake Maróz may suggest an
increase in tropic status.
22
Urszula Szymańska
Fig. 1. Seasonal changes in the composition of net zooplankton in Lake Maróz in the
years 1994–1996 – number share (NS) and weight share (WS)
The food consumed by the vendace was composed of both countable and
uncountable components (Table 3). The countable components identified in the
contents of the digestive tracts of vendaces from Lake Maróz were copepods
(Copepoda) and cladocerans (Cladocera). The countable components were found
in all examined fish (occurrence frequency – 100%), and their weight proportion
was 99.83% (Table 3). From April to November they dominated in terms of both
weight share (97.66 to 100%) and occurrence frequency (Table 3), which shows
that they were major food ingredients.
23
Seasonal changes of food of vendace...
Table 3. Weight share and occurrence frequency of countable and uncountable components
of vendace’s food in Lake Maróz in the years 1994–1996 (mean calculated for
a total of 337 vendaces with full digestive tracts).
Months Food components
99.98
14
100.00
April
189.89
Macrophytes
0.04
0.02
1
7.14
UNCOUNTABLE
TOTAL
COUNTABLE
0.04
189.93
373.44
0.02
100.00
100.00
1
7.14
62
100.00
May
COUNTABLE
Number of digestive
Weight
Weight share
Occurrence
tracts containing food
(mg*specimes-1)
(%)
frequency (%)
of a given category
UNCOUNTABLE
–
–
–
–
TOTAL
373.44
100.00
COUNTABLE
635.86
99.99
49
100.00
0.06
0.01
3
6.12
November
October
September
August
June
Macrophytes
Algae
0.00
0.00
1
2.04
UNCOUNTABLE
0.06
0.01
3
6.12
TOTAL
635.92
100.00
COUNTABLE
23.87
100.00
20
100.00
–
–
UNCOUNTABLE
–
–
TOTAL
23.87
100.00
COUNTABLE
145.84
100.00
39
100.00
–
–
UNCOUNTABLE
–
–
TOTAL
145.84
100.00
COUNTABLE
100.97
97.66
45
100.00
Macrophytes
2.32
0.25
20
44.44
Detritus
0.09
0.09
3
6.67
Algae
0.00
0.00
1
2.27
UNCOUNTABLE
2.41
2.34
22
48.89
TOTAL
103.38
100.00
COUNTABLE
35.89
100.00
108
100.00
–
–
UNCOUNTABLE
–
–
TOTAL
35.89
100.00
COUNTABLE
215.10
99.83
337
100.00
0.35
0.16
24
7.12
0.01
0.01
3
0.89
Macrophytes
Mean
of the Detritus
entire
harvest Algae
UNCOUNTABLE
0.00
0.00
2
0.59
0.36
0.17
26
7.72
TOTAL
215.46
100.00
24
Urszula Szymańska
The order Copepoda was represented by Cyclopoida, Calanoida and
Harpacticoida (Annex 2.). Cyclopoida (mainly Mesocyclops sp.) formed the
dominant group (Annex 2). The proportion of Copepoda in the vendace’s diet
in Lake Maróz changed throughout the year. They dominated in the spring, in April
and May, and in the fall, in September, October and November (Annex 2, Figure
2A). The highest numerical and weight shares (99.32% and 98.82% respectively)
were recorded in April (Annex 2, Fig. 2A). The occurrence frequency of Copepoda
(Figure 2A) and Cladocera (Figure 2B) was high regardless of the values of other
parameters, which shows that they were sought after as food components.
Cladocera were represented by Daphnidae, Bosminidae, Chydoridae,
Leptodora kindtii (Focke), Sididae and Polyphemidae (Annex 2). Cladocera
dominated in the summer (Figure 3B). The domination of Cladocera observed
in June resulted from the presence of Dapnidae (primarily Daphnia cucullata
Sars, as well as D. longispina (O.F. Muller), which were the most important
items of the vendace’s diet (63.47% – Annex 2). Bosminidae (mostly Bosmina
coregoni crassicornis (P.E. Muller) and Bosmina longirostris (O.F. Muller)
dominated in August. At that time Bosminidae were the major components
of the vendace’s diet (Annex 2). As for the other Cladocera found in the food
eaten by vendaces, Leptodora kindtii (Focke) – a predacious cladoceran, 0.2 to
1.5 cm in size, was quite common from June to November. Leptodora kindtii
(Focke) was not present in great numbers (except for June, when it accounted
for 11.11% of the food composition), but being a large cladoceran it had a high
weight proportion in the vendace’s diet (26.91%) over this period (Annex 2). The
frequency of its occurrence was also high, from 25.93% in November to 82.05%
in September (Annex 2). The other cladocerans identified in the food eaten by
the vendace were: Sididae – Sida cristalina (O.F. Muller) and Diaphanosoma
brachyurum (Lievin), Polyphemidae – Bytothrepes longimanus Leydig and
Chydoridae (mainly Chydorus sphaericus (O.F. Muller)). Their numerical and
weight shares did not exceed 6% (Annex 2). Sididae and Polyphemidae were
common in August and September, and Chydoridae – associated with the littoral
zone – were relatively frequent in May (approx. 39%) and in September (approx.
21%) (Annex 2). This may indicate that in these months the vendace kept close
to the littoral zone of the lake.
Seasonal changes of food of vendace...
25
Fig. 2. Seasonal changes in the proportions of Copepoda and Cladocera in the diet
of vendace in Lake Maróz, based on means of the years 1994–1996 (NS – number
share, WS – weight share, OF – occurrence frequency, relative importance index
(RI))
The uncountable components (algea – Spirogyra sp., macrophytes and
detritus) were sporadic only. They were recorded in 26 fish (occurrence frequency
– 7.72%). Fragments of macrophytes were the most common among them
(found in 24 fish; occurrence frequency – 7.12%), but their weight proportion
was as low as 0.16% (Table 3). The uncountable components were identified
in the vendace’s diet in April, June and October. Their weight share and occurrence
frequency were the highest in October (Table 3). This resulted primarily from the
26
Urszula Szymańska
presence of macrophyte fragments, which occurred also in April and June, but
in smaller numbers and at lower frequency. Algae (Spirogyra sp.) were found
in the vendace’s diet in June and October, and detritus only in October (Table 3),
when the vendace begin to form spawning stocks.
The vendace appear to prefer large-form zooplankton, such as big Cladocera
(Daphnidae, Polyphemidae, Leptodora kindtii (Focke)), followed by smaller
ones (Bosminidae, Ceriodaphnia sp.) and copepods capable of escaping. It was
proved experimentally that depending on the availability of particular forms and
fractions of zooplankton, the vendace utilize them in the above-described order
of preference (Szlauer 1965, Brooks 1968, Drenner et al. 1978).
The diet of vendace in Lake Maróz was dominated by Cyclopoida (Annex 2).
Also in the studies carried out by Szypuła (1965) on Lake Legińskie and Mamcarz
& Błoniarz (1995) on Lake Charzykowskie the major food items consumed by
the vendace were Cyclopoida. Both these lakes are eutrophic water bodies, like
Lake Maróz. The diet of vendace in Lake Wigry was dominated by Cyclopoida
(Cyclops vicinus) in spring and autumn (Czarkowski et al. 2007). In mesotrophic
lakes the vendace’s diet is dominated by representatives of Calanoida bigger
than Cyclopoida, e.g. Eurytemora lacustris in Lake Pluszne (Marciak 1962)
or Limnocalanus macrurus in Lake Furnes (Næsje et al. 1991).
Calanoida (mainly Eudiaptomus graciloides) were also identified in the
food consumed by the vendace in Lake Maróz, but only in October (Annex 2).
Harpacticoida, which feed on detritus and can be usually found in bottom deposits,
were recorded in the vendace’s diet sporadically and in low numbers, in May
and November (Annex 2). This shows that in these months the vendace prefer
the near-benthic zone. Also the presence of other countable components in the
food, such as insect larvae and pupae (mostly Chironomidae and Chaoborus sp.),
fish eggs (Cyprinidae in June, Coregonidae in November), water mites
(Hydracarina), ostracods (Ostracoda) and aselli (Asellus aquaticus), may
indirectly indicate that the vendace forage in this zone from June to October. The
fact that over this period the vendace search for food in the near-benthic zone (in
the hypolimnion) was also confirmed by Marciak (1962).
Due to considerable oxygen deficits in Lake Maróz, especially in August,
it seems that the near-benthic zone accessible to the vendace was sublittoral
or even littoral, as indicated by the presence of detritus, algae and macrophytes
in the food (Table 3). Only Szypuła (1965) and Marciak (1979) reported
Seasonal changes of food of vendace...
27
a sporadic occurrence of uncountable components (diatoms and blue-greens)
in the vendace’s diet.
Oxygen deficits in the summer make the vendace leave the pelagial zone,
since the only well-oxygenated water layer is then as narrow as 4–6 m from
the surface (Dembiński 1992). The vendace leave this zone also in the fall,
in order to travel to the spawning grounds. Another reason for the presence
of these components in the food may be the fact that they are carried by water,
since Lake Maróz is exposed to winds, which is conducive to the movement
of bottom sediments and the living organisms that occupy them. This phenomenon
is observed especially during circulations in the spring and fall.
Cladocera dominated in the diet of vendace in Lake Maróz in June and
August (Figure 3B, Annex 2), which coincided with the peak of their occurrence
in the zooplankton (Annex 1). Big Daphnidae are consumed in June, followed
by tiny cladocerans, mainly Bosminidae (Annex 2). This may suggest strong
pressure of planktonophagous fish on zooplankton communities. The domination
of Cladocera in the vendace’s diet was also observed by Szypuła (1970), Ibneeva
& Dorozhkina (1980), Viljanen (1986), Enderlein (1981), Więski (2002) and
Northcote & Hammar (2006). This is related to lower mobility of cladocerans,
compared with copepods (Drenner et al. 1978), and their tendency to form clusters
(Patalas 1954). Such “bites” have a higher calorific value, and the assimilability
of e.g. Daphnia is 70–73% (Bernatowicz et al. 1975). Many authors reported that
Cladocera were present in the vendace’s food for the major part of the year. They
dominated in Lake Constanca from May to November (Becker & Eckmann 1992),
in Lake Pluszne from July to October, and until February they accounted for 30%
of food composition (Marciak 1962), in Lake Furnes from June to September,
and in October and November their weight proportion was at least 30% (Næsje
et al. 1991). The greatest foraging activity and the highest growth rate of the
vendace are observed in summer months (Szypuła 1970, Ciepielewski 1971,
1974, Szczerbowski 1978, Christianus 1995), so over this period body length
increments and weight gains are dependent upon the availability and quality
of food.
Apart from Daphnidae and Bosminidae, also Leptodora kindtii is an
important food ingredient in the vendace’s diet, due to the large body size of this
cladoceran. It was recorded frequently in Lake Maróz, and reached the highest
level in June (Annex 2). Marciak (1962) reported that Leptodora kindtii was
a major food component from August (approx. 10%) to October (approx. 40%),
28
Urszula Szymańska
and its greatest weight proportion was recorded in September (approx. 55%).
Also Næsje et al. (1991) found this cladoceran in the vendace’s food in Lake
Brottum (weight share of approx. 20% in July and approx. 70% in August), and
Becker & Eckmann (1992) in the vendace’d diet in Lake Constanca (approx. 13%
at the end of June and 10% in November).
Conclusions
1. In the years 1994–1996 Cladocera dominated in the composition of zooplankton
in the Maróz Lake The species, not reported from this lake before were found
in current study (Chydorus sphaericus and Bosmina longirostris), which are
considered to be the indicators of fertile waters, and their presence in the lake
may suggest an increase in trophic status.
2. In the spring the vendace’s diet was dominated by Cyclopoide (mainly
Mesocyclops sp.) and in the summer by Cladocera.
3. Cladocera was a dominating component of the vendace’s diet in the Maróz
Lake in June and August, which coincided with the peak of their occurence
in the zooplankton.When the big Daphnidae were consumed in June, they
were followed by tiny cladocerans, mainly Bosminidae. This may suggest
food selectivity and strong pressure of planktonophagus fish on zooplankton
communities.
4. The presence of insect larvae and pupae (mainly Chironomidae, Chaoborus),
fish eggs (Cyprinidae, Coregonidae), Hydracarina, Ostracoda, Asselus
aquaticus, algae and detritus in the diet of vendace Harpacticoida may
indirectly suggest that vendace from June to October consumed the food
resources of near-benthic zone which due to considerable oxygen deficiency
in the Maróz Lake was constituted by sublittoral and even littoral.
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33
Seasonal changes of food of vendace...
Annex 1. Composition of net zooplankton in August in the years 1994–1996
mean 1994–1996
Zooplankton components
Specimes*dm–3
%
CLADOCERA
49.1
69.65
Daphnidae
3.5
4.96
Daphnia cucullata Sars
2.9
4.12
Daphnia longispina O.F. Muller
0.2
0.28
Ceriodaphnia quadrangula (O.F. Muller)
0.2
0.28
Simocephalus vetulus (O.F. Muller)
0.2
0.28
42.4
60.14
2.0
2.84
Bosmina longirostris (O.F. Muller)
40.4
57.30
Bosminidae
Bosmina coregoni crassicornis (P.E. Muller)
Chydoridae
2.0
2.84
Chydorus sphaericus (O.F. Muller)
0.5
0.71
Alona sp.
0.0
0.00
Eurycercus lamellatus (O.F. Muller)
0.1
0.14
Acroperus harpae (Baird)
1.1
1.56
Acroperus harpae (Baird) juv.
0.0
0.00
Camptocercus rectirostris Schoedler
0.0
0.00
Pleuroxus sp.
0.3
0.43
0.4
0.58
Leptodora kindtii (Focke)
Diaphanosoma brachyurum (Lievin)
0.7
0.99
Polyphaemus pediculus (Linne)
0.1
0.14
COPEPODA
21.4
30.35
Cyclopoida
17.9
25.39
10.5
14.89
7.4
10.50
3.5
4.96
Eudiaptomus graciloides
2.1
2.98
Copepodit Calanoida
1.4
1.98
70.5
100.00
Mesocyclops sp.
Copepodit Cyclopoida
Calanoida
TOTAL
34
Urszula Szymańska
Months
Annex 2. Seasonal changes in the composition of vendace’s food in Lake Maróz in the
years 1994–1996
April
1
Mean
number
of prey
per fish
(specimes)
Number
share
(%)
Mean
weight
of prey
per fish
(g)
Weight
share
(%)
3
7604.3
4
99.32
5
187.65
6
98.82
CYCLOPOIDA
7600.0
99.26
187.37
CALANOIDA
4.3
0.06
0.28
CLADOCERA
52.1
0.68
DAPHNIIDAE
17.1
BOSMINIDAE
35.0
Food components
2
COPEPODA
INSECTA
TOTAL
May
COPEPODA
14
8
100.00
9
99.67
98.67
14
100.00
99.66
0.15
2
14.29
0.01
2.24
1.18
6
42.86
0.33
0.22
1.57
0.83
5
35.71
0.19
0.46
0.67
0.35
5
35.71
0.14
0.1
0.00
0.00
0.00
1
7.14
7656.5
100.00
189.89
100.00
0.00
100.00
11307.4
87.86
336.04
89.99
61
98.39
91.10
11197.0
87.00
330.74
88.57
61
98.39
90.63
CALANOIDA
105.0
0.82
5.24
1.40
25
40.32
0.47
HARPACTICOIDA
5.4
0.04
0.06
0.02
3
4.84
0.00
1562.9
12.14
37.24
9.97
56
90.32
8.90
DAPHNIIDAE
765.1
5.94
20.10
5.38
44
70.97
4.22
BOSMINIDAE
765.6
5.95
17.03
4.56
52
83.87
4.62
CHYDORIDAE
32.2
0.25
0.11
0.03
24
38.71
0.06
0.2
0.00
0.15
0.04
5
8.06
0.00
12870.5
100.00
373.43
100.00
695.1
25.80
52.94
8.32
44
89.80
15.84
CYCLOPOIDA
534.2
19.83
46.00
7.23
42
85.71
13.42
CALANOIDA
160.9
5.97
6.94
1.09
29
59.18
2.42
1994.2
74.03
573.01
90.12
49
100.00
83.94
DAPHNIIDAE
1408.0
52.27
394.94
62.11
47
95.92
63.47
BOSMINIDAE
286.9
10.65
6.98
1.10
44
89.80
6.10
CHYDORIDAE
0.0
0.00
0.00
0.00
1
2.04
0.00
Leptodora kindtii
(Focke)
CLADOCERA
TOTAL
COPEPODA
CLADOCERA
June
7
Relative
importance
index
(%)
CYCLOPOIDA
INSECTA
100.00
299.3
11.11
171.09
26.91
32
65.31
14.37
INSECTA
4.4
0.16
9.80
1.54
11
22.45
0.22
FISH EGGS
0.2
0.01
0.10
0.02
2
4.08
2693.9
100.00
635.85
100.00
148.7
28.26
4.30
18.01
19
95.00
25.66
CYCLOPOIDA
138.4
26.30
3.48
14.59
18
90.00
23.75
CALANOIDA
10.3
1.96
0.82
3.42
11
55.00
1.91
375.8
71.46
17.73
74.27
18
90.00
72.06
TOTAL
COPEPODA
CLADOCERA
August
Number
of digestive tracts Occurence
containing prey
frequency
of a given category
(%)
(specimes)
100.00
DAPHNIIDAE
39.3
7.46
3.55
14.90
13
65.00
9.38
BOSMINIDAE
302.6
57.55
11.64
48.75
16
80.00
54.87
CHYDORIDAE
0.1
0.01
0.00
0.00
1
5.00
0.00
Leptodora kindtii
(Focke)
2.6
0.50
1.27
5.30
13
65.00
2.43
SIDIDAE
29.5
5.62
1.18
4.95
15
75.00
5.11
POLYPHEMIDAE
1.7
0.32
0.09
0.37
12
60.00
0.27
INSECTA
1.1
0.21
1.83
7.66
9
45.00
2.28
ROTIFERA
0.4
0.07
0.01
0.06
1
5.00
526.0
100.00
23.87
100.00
TOTAL
0.00
100.00
35
Seasonal changes of food of vendace...
1
2
3
COPEPODA
September
6
7
8
9
111.57
76.50
36
92.31
82.58
CYCLOPOIDA
3400.3
75.74
77.57
53.19
36
92.31
66.83
CALANOIDA
538.2
11.99
34.00
23.31
31
79.49
15.75
548.2
12.21
32.37
22.19
39
100.00
17.22
DAPHNIIDAE
31.7
0.71
9.08
6.22
30
76.92
2.99
BOSMINIDAE
412.4
9.19
13.27
9.09
38
97.44
10.00
CHYDORIDAE
0.9
0.02
0.00
0.00
8
20.51
0.00
Leptodora kindtii
(Focke)
13.9
0.31
6.53
4.48
32
82.05
2.22
SIDIDAE
68.0
1.51
0.93
0.64
35
89.74
1.08
POLYPHEMIDAE
21.3
0.47
2.56
1.76
29
74.36
0.93
INSECTA
1.7
0.04
1.88
1.29
10
25.64
0.19
ROTIFERA
1.1
0.03
0.02
0.02
8
20.51
0.01
OTHER
0.1
0.00
0.00
0.00
2
5.13
0.00
0.1
0.00
0.00
0.00
2
5.13
0.00
TOTAL
4489.6
100.00
145.84
100.00
COPEPODA
1953.5
96.62
83.52
82.74
45
100.00
92.45
CYCLOPOIDA
1464.3
72.42
30.99
30.70
45
100.00
53.66
CALANOIDA
489.3
24.20
52.53
52.04
44
97.78
38.79
64.1
3.17
12.78
12.67
45
100.00
6.63
DAPHNIIDAE
33.6
1.67
4.76
4.72
45
100.00
3.32
BOSMINIDAE
17.7
0.87
0.42
0.41
42
93.33
0.62
CHYDORIDAE
0.2
0.01
0.04
0.04
8
17.78
0.01
Leptodora kindtii
(Focke)
11.2
0.55
5.87
5.83
35
77.78
2.58
SIDIDAE
1.2
0.06
1.66
1.64
5
11.11
0.10
POLYPHEMIDAE
0.2
0.01
0.03
0.03
2
4.44
0.00
INSECTA
3.8
0.19
4.53
4.49
17
37.78
0.92
ROTIFERA
OTHER
0.0
0.4
0.00
0.02
0.00
0.11
0.00
0.11
1
3
2.22
6.67
0.00
0.00
HYDRACARINA
0.0
0.00
0.00
0.00
1
2.22
0.00
OSTRACODA
0.4
0.02
0.09
0.09
1
2.22
0.00
1
2.22
HYDRACARINA
CLADOCERA
October
5
87.72
CLADOCERA
Asellus aquaticus
(L.)
TOTAL
COPEPODA
0.0
0.00
0.02
0.02
2021.9
100.00
100.94
100.00
100.00
0.00
100.00
440.8
79.78
23.51
65.50
106
98.15
75.30
CYCLOPOIDA
388.9
70.39
21.24
59.19
104
96.30
70.46
CALANOIDA
51.9
9.38
2.27
6.31
59
54.63
4.84
HARPACTICOIDA
0.0
0.01
0.005
0.00
3
2.78
0.00
109.5
19.82
10.29
28.67
106
98.15
24.18
DAPHNIIDAE
84.1
15.22
8.71
24.26
100
92.59
20.65
BOSMINIDAE
24.0
4.35
0.58
1.61
101
93.52
3.15
CHYDORIDAE
0.5
0.09
0.20
0.55
10
9.26
0.03
Leptodora kindtii
(Focke)
0.9
0.16
0.80
2.23
28
25.93
0.35
SIDIDAE
0.0
0.00
0.00
0.02
1
0.93
0.00
INSECTA
0.1
0.01
0.12
0.33
6
5.56
0.01
FISH EGGS
1.9
0.36
1.97
5.48
23
21.3
0.51
ROTIFERA
0.2
0.03
0.01
0.02
6
5.56
0.00
552.5
100.00
35.90
100.00
CLADOCERA
November
4
3938.5
TOTAL
100.00