140
H.FÊ. Lin et al.
INTRODUCTION
Environmental factors serve as cues that trigger the physiological
mechanisms which regulate ovulation in teleosts.
For
example, long
—
photoperiod, elevated water temperature and floating vegetation induce a
surge
in
serum
gonadotr0pin (GtH) levels and ovulation in goldfish (Stacey
et
al.
l979a,b).
Appropriate environmental stimuli are often lacking when
fish—are held in captivity, making it necesSary to induce ovulation in order
to
continue
and
to
expand fish culture operations.
Fish
pituitary extract
is
frequently used to induce ovulation in teleosts (see Harvey and Hoar,
1979; Donaldson and Hunter, 1983), although concerne related to the cost of
collection and processing of pituitary glands have led to the search for
:
synthetic chemicals and hormones which stimulate endogenous GtH secretion.
Recent
studies
have
demonstrated
that
GtH
secretion in
teleosts
is
regulated by the actions of a gonadotr0pin—releasing hormone (GnRH) and &
gonadotr0pin release inhibitory factor (GRIF) (see Peter, 1983a,b).
The
'
preovulatory surge of GtH that is responsible for ovulation may be regulated
by a stimulation by GnRH and/or a release from inhibition by GRIF.
Attempts
to
induce
ovulation by the injection of long—acting analogues of mammalian
GnRH have met with
limited
success
in
cypriniform species such as the
goldfish (Chang and Peter 1983a; Sokolowska et al. 1984) and common carp
(Billard
1983).
Recent
studies have EEbŒE that dopamine functions as
a
GRIF
in goldfish by blocking the spontaneous release of GtH and modulating
the
actions
of
GnRH
(Chang and Peter 1983b; Chang et al. 1984a,b).
Furthermore, injection of pimozide (PIM), a dopamine receptor antagonist,
greatly potentiates the action of GnRH on GtH release, and this combination
is
an
effective means
of
inducing ovulation in goldfish (Chang and Peter
1983a; Sokolowska
1984, 1985a,b), common carp (Billard et al. 1983),
Chinese
loach
(Lin ÊË.ËË: 1985),African catfish (de Leeuw et
rainbow
trout
(Billard
1984) and coho salmon (Van DEË'ËÉàak et al1986); in the European eel pimozide has been shown to potentiate thë“àEîäon
of
an
LHRH
analogue on GtH release (Dufour et al. 1984).
In
this
paper,
WË will9present
the
results
of
studies which investigate
the
effects of [D—Ala , Pro —N—ethylàmide]—luteinizing hormone-releasing
hormone
(LHRH—A) alone and in combination with PIM on serum GtH levels and
ovulation in
common
carp
(Cyprinus carpio), silver carp
molitrix) and bream (Parabramis pekihËEËiè).
In addition, tests on the
effects
of
reserpine (RES), a drug which blocks catecholamine synthesis,
together with LHRH—A on ovulation in common carp and loach (Paramisgurus
dabyranus) are reported.
,
_————___—___——
…
'
Carp were obtained from ponds at Zhongshan University and loach were
obtained from a local supplier (Guangdong Province, China).
Sexually mature
(=preovulatory) females were selected for experiments on the basis of a soft
and
distended abdomen.
During experiments, fish were held outdoors at
ambient water
temperature in either 250 l aquaria (loach), 3 X 4 m fenced
areas
in holding ponds (common carp and bream) or 4 m diameter circular
cement
tanks
(silver carp).
was
purchased from the Ningbo Fish Hormone Factory, Zhekian8
Province,
China.
PIM was
a
gift from Janssen Pharmaceuticals Ltd., Beerse,
Belgium and RES was purchased from Sigma, St. Louis, Mo., USALHRH—A was
H.FÊ. Lin et al.
INTRODUCTION
Environmental factors serve as cues that trigger the physiological
mechanisms which regulate ovulation in teleosts.
For
example, long
—
photoperiod, elevated water temperature and floating vegetation induce a
surge
in
serum
gonadotr0pin (GtH) levels and ovulation in goldfish (Stacey
et
al.
l979a,b).
Appropriate environmental stimuli are often lacking when
fish—are held in captivity, making it necesSary to induce ovulation in order
to
continue
and
to
expand fish culture operations.
Fish
pituitary extract
is
frequently used to induce ovulation in teleosts (see Harvey and Hoar,
1979; Donaldson and Hunter, 1983), although concerne related to the cost of
collection and processing of pituitary glands have led to the search for
:
synthetic chemicals and hormones which stimulate endogenous GtH secretion.
Recent
studies
have
demonstrated
that
GtH
secretion in
teleosts
is
regulated by the actions of a gonadotr0pin—releasing hormone (GnRH) and &
gonadotr0pin release inhibitory factor (GRIF) (see Peter, 1983a,b).
The
'
preovulatory surge of GtH that is responsible for ovulation may be regulated
by a stimulation by GnRH and/or a release from inhibition by GRIF.
Attempts
to
induce
ovulation by the injection of long—acting analogues of mammalian
GnRH have met with
limited
success
in
cypriniform species such as the
goldfish (Chang and Peter 1983a; Sokolowska et al. 1984) and common carp
(Billard
1983).
Recent
studies have EEbŒE that dopamine functions as
a
GRIF
in goldfish by blocking the spontaneous release of GtH and modulating
the
actions
of
GnRH
(Chang and Peter 1983b; Chang et al. 1984a,b).
Furthermore, injection of pimozide (PIM), a dopamine receptor antagonist,
greatly potentiates the action of GnRH on GtH release, and this combination
is
an
effective means
of
inducing ovulation in goldfish (Chang and Peter
1983a; Sokolowska
1984, 1985a,b), common carp (Billard et al. 1983),
Chinese
loach
(Lin ÊË.ËË: 1985),African catfish (de Leeuw et
rainbow
trout
(Billard
1984) and coho salmon (Van DEË'ËÉàak et al1986); in the European eel pimozide has been shown to potentiate thë“àEîäon
of
an
LHRH
analogue on GtH release (Dufour et al. 1984).
In
this
paper,
WË will9present
the
results
of
studies which investigate
the
effects of [D—Ala , Pro —N—ethylàmide]—luteinizing hormone-releasing
hormone
(LHRH—A) alone and in combination with PIM on serum GtH levels and
ovulation in
common
carp
(Cyprinus carpio), silver carp
molitrix) and bream (Parabramis pekihËEËiè).
In addition, tests on the
effects
of
reserpine (RES), a drug which blocks catecholamine synthesis,
together with LHRH—A on ovulation in common carp and loach (Paramisgurus
dabyranus) are reported.
,
_————___—___——
…
'
Carp were obtained from ponds at Zhongshan University and loach were
obtained from a local supplier (Guangdong Province, China).
Sexually mature
(=preovulatory) females were selected for experiments on the basis of a soft
and
distended abdomen.
During experiments, fish were held outdoors at
ambient water
temperature in either 250 l aquaria (loach), 3 X 4 m fenced
areas
in holding ponds (common carp and bream) or 4 m diameter circular
cement
tanks
(silver carp).
was
purchased from the Ningbo Fish Hormone Factory, Zhekian8
Province,
China.
PIM was
a
gift from Janssen Pharmaceuticals Ltd., Beerse,
Belgium and RES was purchased from Sigma, St. Louis, Mo., USALHRH—A was