induced spa wning
129
III
—
INFLUENCE OF ENVIRONMENTAL AND SOCIAL FACTORS ON SPONTANEOUS AND
HORMONAL
INDUCED
It
is
well
established
that
in cyprinids water temperature plays an
important role in gametogenesis development (review of PETER and CRIM 1979).
In common
carp,
sexual maturity is reached earlier in warm climates than in
temperate conditions
and
GUPTA
1975 obtained a precocious maturity in carp
held in warm water aquaria (23°C). Male and female tench maintained all year
in a heated pond (6°C above ambiant temperature) showed an accelerated sper—
matogenesis and
vitellogenesis compared to the control (BRETON et al.
1980a
et b)…
However
daylenght may interfere with temperature since in an indian
carp
a
constant
short
daylength retarded the maturity of gonads in female
(VERGHESE 1970) and in male of common carp (WEIL 1981 — showed in BILLARD et
al.
1982)°
In
practice
the
influence of environmental
factors on induction of a
rematuration of
the
gonad after hormonal induced spawning is used in common
carp,
chinese
carp
and
indian carp
(respectively HORVATH 1980a ; LIN 1982
and FREEZE and
CRAWFORD
1983 ; BHOWNICK et al 1977)° The combination of high
water
temperature and good feeding induces within 2 months the maturation of
the gonad and a second spawning
may be
induced with hormonal
treatment when
temperature required for ovulation is provided.
With
respect
to
the
end of gametogenesis i.e. spermiation and ovula—
tion, different
factors
may
improve
the
spontaneous process. In goldfish
spermiation is promoted a progressive rise in temperature which is in corre—
lation with
an
increase
in
plasma
GtH
(GILLET et al.
1977)
;
ovulation
occurs
at
20—21°C
(YAMAMOTO et al.
1966., STACEY et al. 1979b) in presence
of absence of aquatic vegetation while it occurs at 12°C only in the presen—
ce
of
vegetation (STACEY et al 1979b). Furthermore ovulation in goldfish is
highly synchronized
with
photoperiod
(STACEY et al 1979b). Social factors
may act
as
well"
In
female
goldfish YAMAZAKI 1965 and YAMAMOTO et al.
1966
indicate that
the
presence
of sexually active males induce ovulation. For
males KYLE
et
al.
1985
report that the presence of a receptive female or
stimulus pairs
of
spawning goldfish induce an increase in expressible milt
volumes and
plasma
GtH.
NIKITINA and GODOVICH
1983 have demonstrated that
the dynamics
of sex hormones in the blood of male common carp depend on the
presence or
absence
of spawning in the females placed with them. In pratice
in China it is possible to induce spawning of female mud carp by the presen—
ce
of active
female spawners
(injected with pituitary extract) when they are
held in a common spawning pond (LIN 1982).
Environmental factors modulate the response to hormonal treatment. Tem—
perature is an important factor for :
_
_
—
the injection interval
—
the
latency of the ovulatory and milting response as demonstrated in
female and
male
common
and
chinese carp
(HORVATH 1978b) and in female gold—
fish (STACEY et al. 1979b) following pituitary or HCG
—
the
time
of
overrippening of ovulated oocytes. It depends on carp
species.
(HORVATH 1978b)
-
,
—
the success of spawning i.e. the maturation of breeders.
Oxygen concentration
also
conditions the success of hypophysation (HORVATH
and PETERI
1980).
These,
authors
demonstrated that both, water temperature
and the
amount
of
oxygen,
strongly influence the maturation of
SPawners.
If
one
of
these
parameters
is
lower
than required the adverse
Effect cannot be counter balanced by the higher level of the other factor,
Time
of
injection
(since
there
is
evidence of a possible
circadian
rythm of
oocyte
sensitivity, BIENIARZ et al., summary this
well
as
the
presence
of
vegetation, or a precise photoperiod, or spawn1ng fish
may be also important to ensure a maximal efficiency of hormonal treatment.