1067-4136/02/3302- $27.00 © 2002
Russian Journal of Ecology, Vol. 33, No. 2, 2002, pp. 104–108. Translated from Ekologiya, No. 2, 2002, pp. 115–119.
Original Russian Text Copyright © 2002 by Ivanov, Semenova.
Dynamism is among the basic properties of bio-
cenoses, as they are characterized by permanent
changes in the state and life activities of their compo-
nents, the qualitative and quantitative ratios of popula-
tions, and the composition of dominant species.
Periodic changes in the level of the Caspian Sea lead
to structural rearrangements in biocenoses of the Volga
Delta, which affect life conditions for all their compo-
nents, including commercially important ﬁsh species.
Fish populations are strongly affected by helminth
invasions, especially pathogenic are metacercariae and
maritae of ﬂukes, many of which can cause epizootics.
In this study, an attempt was made to analyze
changes in ﬁsh infestation by ﬂukes over a long period
of time and to relate these changes to the dynamics of
the qualitative and quantitative composition of ﬂukes
and the distribution of their hosts with respect to life
MATERIAL AND METHODS
In the course of studies performed in the Volga Delta
from 1976 to 1998, 3068 ﬁsh belonging to 34 species
were investigated by the method of complete helm-
inthological dissections. Flukes were stained with car-
mine, dehydrated in alcohol solutions of increasing
strength, clariﬁed in dimethyl phthalate, and embedded
in Canada balsam (Sudarikov and Shigin, 1965).
In the description of the results, zones of the Volga
Delta are indicated according to Belevich (1963) and
the extensiveness of invasion is characterized by the
index (EI) determined as the percent ratio of infested
individuals (hosts) to the total number of individuals
RESULTS AND DISCUSSION
In the study period, 61 ﬂuke species of trematodes
belonging to eight orders and 18 families were found in
ﬁsh; 39 species were at the stage of metacercaria, and
24 were at the stage of marita (three of them were found
at both developmental stages). For some species, the
long-term dynamics of the extensiveness of invasion
could be traced.
In the 1930s and 1940s, the level of the Caspian Sea
began to decrease. This process continued in the 1960s
and 1970s. In 1977, the sea level fell to the lowest mark
(–29.03 m). Because of increasing irreversible losses of
annual ﬂow discharge, the levels and duration of spring
ﬂoods decreased. In this period, transformations
occurred in the delta biotopes (ﬁgure), which included
the increase in the areas of shoals, the formation of new
spits, and active overgrowing in the avandelta and the
zone of delta islands (Zhivoglyad, 1984, 1995).
In the 1950s and 1960s, the avandelta was formed
and populated by resident ﬁsh species of the lake–river
complex. The concentration of ﬁsh increased owing to
the increasing proportion of resident species, whereas
the proportion of semianadromous species decreased in
this period (Tryapitsyna, 1965; Kizina, 1995).
In the 1970s, the ﬁsh species preferring lotic water
bodies (Caspian roach, white bream, and perch) were
dominant in the lower delta, and the inhabitants of
shoals with a slow current and abundant vegetation
(rudd, tench, and crucian carp) were dominant in the
zone of delta islands; the zone of bays was intermediate
with respect to the type of water bodies and the species
composition of ﬁsh (Kizina, 1995).
The period of decreasing sea level was characterized
by the prevalence of the phytophilic and limnophilic
complexes of benthic invertebrates. With respect to bio-
Dynamics and Structural Changes of the Fluke Fauna
in Fish of the Volga Delta Caused by the Rise
of Water Level in the Caspian Sea
V. M. Ivanov and N. N. Semenova
Astrakhan State Biosphere Reserve, nab. r. Tsarev 119, Astrakhan, 414021 Russia
Received October 26, 2000
—Changes in the Caspian Sea level and anthropogenic inﬂuences on biocenoses of the Volga Delta
periodically result in the changes of dominant species among animal helminths. An abrupt rise of the sea level
since the mid-1970s caused structural rearrangements in the ﬂuke fauna of ﬁsh in the 1990s: the species whose
development is connected with mollusks of the rheophilic complex became dominant.
: structural changes, ﬂuke fauna, dominant species, hosts of trematodes.