nous development (which is uncommon for stur-
geons), decreases in the strength of their mem-
branes, and by degeneration of 15% of the germ
cells. Simultaneously, the remaining oocytes under-
going cytoplasmic growth continued to degenerate.
In the Kolyma River population up to 81–83% of
all females had various defects in germ cells in 1988
and I989 (Akimova & Ruban 1993, Ruban & Aki-
mova 1993). Just as in the Indigirka population, de-
generation of some oocytes was observed during
the period of cytoplasmic growth, in some females
repeatedly, and amitotic divisions of oocytes were
also found. Degeneration of oocytes at the time of
growth was higher (upto20% of oocytes) in fe-
males of the Kolyma River population than in fe-
males of other populations. Defects in oocyte mem-
branes resulted in 50–100%of mature eggs having a
deformed, angular shape. The gelatinous envelopes
contained inclusions of uncertain content, which
were absent in egg envelopes of sturgeon from the
Lena and Indigirka populations. In some females of
the Kolyma River population, destruction of the
nuclear membrane was observed in still immature
oocytes. This destruction caused the disintegration
of the nuclei.
Some oocytes had evidently degenerated during
the period of cytoplasmic growth in females from
the Yenisey River population. Also an amitotic di-
vision of oocytes, which caused the degeneration of
the dividing cells, was observed. In some females
the oocyte envelopes became locally thinner during
the period of growth in almost 50% of oocytes. We
also observed extensive deformation oocytes, ap-
pearance of cavities with foreign body inclusions
under the oocyte envelopes and among yolk gran-
ules, and mass resorption of mature eggs in some
females. Unspawned eggs were present in gonads of
some females after spawning. In general, the dis-
covered abnormalities of gametogenesis in the Ye-
nisey population were not so numerous as in the
Kolyma or Indigirka River populations. This en-
abled us to declare this phenomenon as an initial
state of pathological development and functioning
of the reproductive system (Akimova et al. 1995).
Disturbances in gametogenesis of females from the
Yenisey River are probably caused by a high level ofbasins: 1401 and 504 metric tons per year, respec-
tively (Figure 2). In other Siberian rivers the stur-
geon catch was much smaller and there was no spe-
cialized sturgeon fishery. The highest catch in the
Lena River was 189.9 metric tons in 1943. The pop-
ulations of two sturgeon subspecies, the nominalA.
baerii baerii of the Ob River basin and the East-Sib-
erianA.baerii stenorrhynchusof the Yenisey River,
were especially affected by fishing. The third sub-
species,A. baerii baicalensis,is at present extremely
rare and has been included in the Red Data Book of
the Russian Federation (Kolosov 1983).
Histrological data on the effect of pollutionDisturbances in the reproductive system are often
correlated with worsening conditions of the envi-
ronment, especially high levels of chemical pollu-
tion. Our long-term histological studies (methods in
Roskin & Levinson 1957) on the development and
functioning of the reproductive system in Siberian
sturgeon inhabiting East Siberia showed abnormal
gametogenesis in individuals from the Lena, Indi-
girka, Kolyma, and Yenisey rivers.
Between 1964 and 1977, only single cases of de-
generation ofoocytesduring the period of cytoplas-
mic growth were reported in females of the Lena
River population (Akimova & Ruban 1993). But in
1986 the number of females with such defects was
close to 59% (23 of 39 females studied). New types
of anomalies appeared in these females: some of
them had many unspawned eggs, and amitotic divi-
sion of sex cells and degeneration of the nuclear
membrane in oocytes during vitellogenesis were
characteristic for many females (Akimova & Ru-
ban 1995).
Similarly, but in a shorter period of time and to a
greater extent, the state of the reproductive system
in females of the Indigirka River population also
changed (Ruban & Akimova 1991, Akimova & Ru-
ban 1993). The percent of females of different ages
with partially degenerated oocytes during the peri-
od of cytoplasmic growth increased within four
years (1984–1987) from 77 to 100%. In some females
degeneration occurred repeatedly. The growth pe-
riod of the oocytes was characterized by asynchro-