102
K. Bieniarz
SEX DIFFERENTIATION
Sex
cells
in
cyprinids, like those in other teleosts, originate from
mordial
germ
cells
(PGO).
In
the
later
stages of ontogenesis,
PGO
are
fonæd
from
epithelial
cells
(Persov,
1975).
According
to
Persov
(1975)
the
PGC
should
be
considered
as
sex
cells
from
the
earlest
stages of embryonic daœ—
lopment
up
to
the
period
of
gonad formation and the start of active mitoüc
division.
From
that
stage the cells are oogonia or spermatogonia which difw
from
the
PGO
by their larger size
(9—22 pm) (Johnston, 1951 ; Persov, 197Œ,
a
distinct
demarcation
between
the
nucleus
and
the
cytoplasm,
their
densdy
stained
nucleus,
chromophobic
cytoplasm,
higher
cytoplasm/nucleus ratio and
possibly some remnants of yolk.
The
number of PGO
in cyprinid fish, ranging between 1 and 105, is similar
to
that
in other vertebrates.
It
seems
to
show some
intraspecific variability,
Riazanceva and Sakun
(1980) found a range of 22—62 PGO in one carp population,
and between 3
and
11
in another.
In
1—day larvae of Rumanian carp, Nedelea æm
Steopoe
(1970)
found
about
40
PGO.
Also,
Riazanceva
and
Sakun
(1980)
fow
that
at
a
given age,
the
number
of
PGO
per
individual
did
not
depend on üæ
length and mass
of
the
carp
larva
;
however,
at
20—40
days after hatchù@,
their number
increased after mitotic
division.
En
24—day tench, Dlugosz et aL
(1983)
found
1
to
4
PGO.
PGO
migration to the medoserm along a different pæm
terminates rather quickly, and a few hours after hatehing the PGO are found in
the
place of the future gonad.
In
early stages of embryonic development, the
PGO,
concentrated
in
the
vicinity
of
the
originating
Wolffian
duct,
fbrm
chains between the kidney and gut (Persov, 1975).
The
first
stages of gonad differentiation consist of an increase in the
number
of
sex
and
somatic
cells
due
to
mitosis
and the
appearance
of germinal
epithelium.
Gonad
formation,
which
is
similar
in
all
teleosts
(Persov,
results
from
an
increase
in
the
number
of
the peritoheal cells which produces
folds
in
the
body dorsal wall.
Yamamoto
and
Tajishima
(1968) have shown that
ï
carp
males
(Oyprinus carpio L.) are heterogametic, and Œowinskaya (1969) and
Stanley
(1976),
using the method of artificial gynogenesis,
have
proved that
carp
and
grass
carp
females, respectively, are homogametic. Gonad differentia—
tion
has
been
mainly studied in carp and some other species (table 1). Solewski
(1957)
carried
out investigations on carp of the upper Vistula river in Po—
land
where
pond water temperature is between 2 and 5°O in winter,
6
and 15°C
in autumn and spring and 16 and 25°C in summer. At 95 days after fertilization
the
gonads appear as thin pale pink threads, covered by a single layer of epi—
thelial
cells
and
a
thin
layer of connective tissue which penetrate into the
gonad together with the blood vessels ; scattered differentiated sex cells oc—
cur
simultaneously. In 156—day old fry, the gonads appear as thin, transparent
pale pink,
jelly—like threads which become connective tissue at the posterior
ends.
In
the
gonads
of
some
fish,
large
sex
cells
develop into oogonia and
then into oocytes forming, together with other gonadal elements, the ovary. In
the
gonads
of
other
fish,
the
large sex cells disappear and are replaced by
smaller ones having a nucleus and surrounded by connective tissue ; these are
the
presumptive
testes.
Therefore,
under
climatic
conditions
in
Poland,
carp
gonads begin to develop at 95 days after fertilization and are sexually differentiated
156
days later. Pospisil and Smisek (1971) in Ozechoslovakia concluded
that
sex
differentiation
in
carp
gonads usually occurs after 210 days 0f
age
and
lasts
up
to
about
300
days and that this differentiation depends on
body weight but not on temperature.
Gonad
differentiation
occurs
earlier
in
big fish than in small ones of the same age. However, gonad differentiation in
fish kept for 70 days at 5.1°O followed a pattern similar to that of fish kept
for
the
same
period of time at 15.7°O,
but the authors
did not take
into con—
sideration the effects of temperature on body weight.
K. Bieniarz
SEX DIFFERENTIATION
Sex
cells
in
cyprinids, like those in other teleosts, originate from
mordial
germ
cells
(PGO).
In
the
later
stages of ontogenesis,
PGO
are
fonæd
from
epithelial
cells
(Persov,
1975).
According
to
Persov
(1975)
the
PGC
should
be
considered
as
sex
cells
from
the
earlest
stages of embryonic daœ—
lopment
up
to
the
period
of
gonad formation and the start of active mitoüc
division.
From
that
stage the cells are oogonia or spermatogonia which difw
from
the
PGO
by their larger size
(9—22 pm) (Johnston, 1951 ; Persov, 197Œ,
a
distinct
demarcation
between
the
nucleus
and
the
cytoplasm,
their
densdy
stained
nucleus,
chromophobic
cytoplasm,
higher
cytoplasm/nucleus ratio and
possibly some remnants of yolk.
The
number of PGO
in cyprinid fish, ranging between 1 and 105, is similar
to
that
in other vertebrates.
It
seems
to
show some
intraspecific variability,
Riazanceva and Sakun
(1980) found a range of 22—62 PGO in one carp population,
and between 3
and
11
in another.
In
1—day larvae of Rumanian carp, Nedelea æm
Steopoe
(1970)
found
about
40
PGO.
Also,
Riazanceva
and
Sakun
(1980)
fow
that
at
a
given age,
the
number
of
PGO
per
individual
did
not
depend on üæ
length and mass
of
the
carp
larva
;
however,
at
20—40
days after hatchù@,
their number
increased after mitotic
division.
En
24—day tench, Dlugosz et aL
(1983)
found
1
to
4
PGO.
PGO
migration to the medoserm along a different pæm
terminates rather quickly, and a few hours after hatehing the PGO are found in
the
place of the future gonad.
In
early stages of embryonic development, the
PGO,
concentrated
in
the
vicinity
of
the
originating
Wolffian
duct,
fbrm
chains between the kidney and gut (Persov, 1975).
The
first
stages of gonad differentiation consist of an increase in the
number
of
sex
and
somatic
cells
due
to
mitosis
and the
appearance
of germinal
epithelium.
Gonad
formation,
which
is
similar
in
all
teleosts
(Persov,
results
from
an
increase
in
the
number
of
the peritoheal cells which produces
folds
in
the
body dorsal wall.
Yamamoto
and
Tajishima
(1968) have shown that
ï
carp
males
(Oyprinus carpio L.) are heterogametic, and Œowinskaya (1969) and
Stanley
(1976),
using the method of artificial gynogenesis,
have
proved that
carp
and
grass
carp
females, respectively, are homogametic. Gonad differentia—
tion
has
been
mainly studied in carp and some other species (table 1). Solewski
(1957)
carried
out investigations on carp of the upper Vistula river in Po—
land
where
pond water temperature is between 2 and 5°O in winter,
6
and 15°C
in autumn and spring and 16 and 25°C in summer. At 95 days after fertilization
the
gonads appear as thin pale pink threads, covered by a single layer of epi—
thelial
cells
and
a
thin
layer of connective tissue which penetrate into the
gonad together with the blood vessels ; scattered differentiated sex cells oc—
cur
simultaneously. In 156—day old fry, the gonads appear as thin, transparent
pale pink,
jelly—like threads which become connective tissue at the posterior
ends.
In
the
gonads
of
some
fish,
large
sex
cells
develop into oogonia and
then into oocytes forming, together with other gonadal elements, the ovary. In
the
gonads
of
other
fish,
the
large sex cells disappear and are replaced by
smaller ones having a nucleus and surrounded by connective tissue ; these are
the
presumptive
testes.
Therefore,
under
climatic
conditions
in
Poland,
carp
gonads begin to develop at 95 days after fertilization and are sexually differentiated
156
days later. Pospisil and Smisek (1971) in Ozechoslovakia concluded
that
sex
differentiation
in
carp
gonads usually occurs after 210 days 0f
age
and
lasts
up
to
about
300
days and that this differentiation depends on
body weight but not on temperature.
Gonad
differentiation
occurs
earlier
in
big fish than in small ones of the same age. However, gonad differentiation in
fish kept for 70 days at 5.1°O followed a pattern similar to that of fish kept
for
the
same
period of time at 15.7°O,
but the authors
did not take
into con—
sideration the effects of temperature on body weight.