104
K. Bieniarz
ln_silver carp,
Emelianova
(1976)
found
that
larval
gonads began to fœm
at
5
(n‘
8
days
after
hatching,
when
the
larvae
were
9—10
mm
long and 50—75
days old.
Sex
differentiation
started
when
they were 120 mm long and about90
days old and terminated when they were 160—170 mm long.
In
Cirrhinus
mrigala (Parihar,
1980),
the
PGC
appear
in
5.5—mm
long
vae
96
h
after
fertilization.
The
gonads form and cytological differentiation
starts
when
the
fish
are
8
mm
long
;
at
the
age
of
1.5 months
(larval length
35 mm), sex can be histologically determined.
Very few data are available on the differentiation of the specialized so—
‘
matic
cells,
e.g.
steroidogenic cells. Davies and Takashima (1980) identified
,
12 kinds of stroma cells in the second
(ovarian—like) and third (transitional)
[
type
of
carp
gonads at 65 days of age.
In
the
third
type,
the
stroma
cells,
‘
linked to oocyte—like cells, were also degenerating.
Abraham
et
al.
(1984)
found
that
prefollicular
cells
appear
in
common
carp
at
the
earliest
stages of oocyte development
(early meiotic prophase)
these
cells,
close
to
the
oocyte,
later
develop into follicular cells. During
that
period,
no
distinct
thecal
cells
are
identified.
They appear later from
the
stroma
cells
surrounding the
follicular
cells,
indicating that steroid—
producing cells appear after sex differentiation.
PUBERTY
Very
little
has
been
published on the development of hormonal relationships in the gonadal—pituitary—hypothalamic axis in fish prior to puberty sex
steroid
production in carp is similar in females and males up to the time of
sexual
maturity
(Godovich
et
al.,
1984).
Androgens,
estrogens and progestins
occur
at
all
stages of ontogenesis, with androgens being the highest in both
sexes.
Sex differences with respect to steroid hormones starts to be evidenced
as
late
as
2
years
of
age,
and
then
only the estradiol levels in the females
]
increase.
Hormonal
sex
differences
become
evident
with
the
process
of vitellogenesis.
At
that
time,
the
level
of
17 B—estradiol
augmente
in
female
goldfish
(Schreck and Hopwood, 1974). Other studies (Musialek, 1985) have shown that no
diurnal
changes occur in the plasma steroid levels of maturing carp. However:
such
changes
were
found
in
the
plasma
of
mature
carp,
irrespective
of
sex
(Bieniarz et al., 1985).
Maturational
GtH
(mGtH)
in
the
plasma of sexually maturing cyprinids undergoes annual changes, reaching maximal levels in both sexes during spawningThis
has
been
ascertained
in
carp
(Bieniarz et al.,
1979,
the
Fish
Reproduc—
tion
Physiology
Research
Group,
1978),
goldfish
(Cook and. Peter,
1980)
and
tench
(Breton et al., 1980a,b), although the latter authors found an
additio—
nal
peak
of
mGtH
occurring in sexually—maturing tench males and females in
winter,
a
few
months
before
spawning.
Also,
in
the maturing 2—year old female
carp,
Billard
et
al.
(1978)
observed
the
highest mGtH level in summer.
This
may
indicate
that
plasma mGtH in maturing cyprinids undergoes changes during
a
1—year period,
as
in
mature
fish,
although we have no data as to the age at
which fish mGtH starts to appear in the blood plasma.
Growth
rate
aside,
cyprinids reach sexual maturity at various ages,
de—
pending on the species
(or sub—species) and the latitude or water temperature
and
the
kind
of
water
body in which they are found.
0rlova
(1975)
studyingh
bream
in
Lithuanian
lakes
reported
that
they reach maturity at 6—7 years
of
age
in
some
lakes
and
at
9
years
in others.
Females with varying body lengths
K. Bieniarz
ln_silver carp,
Emelianova
(1976)
found
that
larval
gonads began to fœm
at
5
(n‘
8
days
after
hatching,
when
the
larvae
were
9—10
mm
long and 50—75
days old.
Sex
differentiation
started
when
they were 120 mm long and about90
days old and terminated when they were 160—170 mm long.
In
Cirrhinus
mrigala (Parihar,
1980),
the
PGC
appear
in
5.5—mm
long
vae
96
h
after
fertilization.
The
gonads form and cytological differentiation
starts
when
the
fish
are
8
mm
long
;
at
the
age
of
1.5 months
(larval length
35 mm), sex can be histologically determined.
Very few data are available on the differentiation of the specialized so—
‘
matic
cells,
e.g.
steroidogenic cells. Davies and Takashima (1980) identified
,
12 kinds of stroma cells in the second
(ovarian—like) and third (transitional)
[
type
of
carp
gonads at 65 days of age.
In
the
third
type,
the
stroma
cells,
‘
linked to oocyte—like cells, were also degenerating.
Abraham
et
al.
(1984)
found
that
prefollicular
cells
appear
in
common
carp
at
the
earliest
stages of oocyte development
(early meiotic prophase)
these
cells,
close
to
the
oocyte,
later
develop into follicular cells. During
that
period,
no
distinct
thecal
cells
are
identified.
They appear later from
the
stroma
cells
surrounding the
follicular
cells,
indicating that steroid—
producing cells appear after sex differentiation.
PUBERTY
Very
little
has
been
published on the development of hormonal relationships in the gonadal—pituitary—hypothalamic axis in fish prior to puberty sex
steroid
production in carp is similar in females and males up to the time of
sexual
maturity
(Godovich
et
al.,
1984).
Androgens,
estrogens and progestins
occur
at
all
stages of ontogenesis, with androgens being the highest in both
sexes.
Sex differences with respect to steroid hormones starts to be evidenced
as
late
as
2
years
of
age,
and
then
only the estradiol levels in the females
]
increase.
Hormonal
sex
differences
become
evident
with
the
process
of vitellogenesis.
At
that
time,
the
level
of
17 B—estradiol
augmente
in
female
goldfish
(Schreck and Hopwood, 1974). Other studies (Musialek, 1985) have shown that no
diurnal
changes occur in the plasma steroid levels of maturing carp. However:
such
changes
were
found
in
the
plasma
of
mature
carp,
irrespective
of
sex
(Bieniarz et al., 1985).
Maturational
GtH
(mGtH)
in
the
plasma of sexually maturing cyprinids undergoes annual changes, reaching maximal levels in both sexes during spawningThis
has
been
ascertained
in
carp
(Bieniarz et al.,
1979,
the
Fish
Reproduc—
tion
Physiology
Research
Group,
1978),
goldfish
(Cook and. Peter,
1980)
and
tench
(Breton et al., 1980a,b), although the latter authors found an
additio—
nal
peak
of
mGtH
occurring in sexually—maturing tench males and females in
winter,
a
few
months
before
spawning.
Also,
in
the maturing 2—year old female
carp,
Billard
et
al.
(1978)
observed
the
highest mGtH level in summer.
This
may
indicate
that
plasma mGtH in maturing cyprinids undergoes changes during
a
1—year period,
as
in
mature
fish,
although we have no data as to the age at
which fish mGtH starts to appear in the blood plasma.
Growth
rate
aside,
cyprinids reach sexual maturity at various ages,
de—
pending on the species
(or sub—species) and the latitude or water temperature
and
the
kind
of
water
body in which they are found.
0rlova
(1975)
studyingh
bream
in
Lithuanian
lakes
reported
that
they reach maturity at 6—7 years
of
age
in
some
lakes
and
at
9
years
in others.
Females with varying body lengths