Comfm! of sex in Cyprinids
185
used cold shocks between 0 and 80 and durations from 30—90 minutes at varying
intervals after inseminâtion with an average of 13 and 22 Z,at 5 and 15 minu—
tes, respectively. One potentially significant procedure in this study was
that eggs were not
inseminated until 2 hours after stripping. Changes occur
in ova, either through delayed stripping or by holding after stripping, which
may have an effect onpolar body retentionc
Efforts with
grass
carp have been extensive as gynogenesis was the basis
of producing monosex fish for an ecological study (Stanley, 1976c,d). A total
of over 58 million eggs yielded about 45,000 diploids (Stanley, 1979) or only
about eight diploids in 10,000 eggs. My personal experience, also without
dærmalshocking, has been production of 1.8—2.2/10,000. Stanley (1976b) pro—
duced 56 diploids/10,000 eggs ; however, if only those females that produced
diploids were conàidered, production was about 300/10,000° Enhancement of
diploidization througl1thermal shocks as suggested by carp studies has been
inconsistent… Most treatments have been cold shocks with temperatures ranging
from 2—18C, durations of 15—60 minutes at assumed optimal intervals of 1—15
minutes after inseminatione Yield has been little enhanced ; usually morta—
lity was nearly complete, suggesting sensitivity to low temperatures as repor—
ted by Stott and Cross (1973). Surprisingly, few attempts have been made with
elevated temperatures, although Stanley (1979, 1981) reported moderate impro—
vement.
Near lethal levels may be required ; Frank (1974) reported that carp
eggs were killed at â2—45C in 10 minutes and Stanley (1981) found that 35C
for 5 minutes killed grass carp eggs.
Similarly, inducement of gynogenesis in silver carp (Mirza and Shelton,
in prep…) and bighead carp were most promising with heat shock° Maximum yiekk
for both species occurred at 1—5 minutes with shocks of 32—34C for 1—2 minutes
Cold shocks of 5
and 22C produced virtually no diploids. No shock controls
yielded less than 10/10,000, while optimal shock increased production by 10
times. From eight silver carp females, 1 million eggs were shocked but only
899 diploids were produced. Likewise, from four bighead carp females, 1.2
million eggs were shocked and only 224 diploids developed. Subsequently, I
shocked 630,000 silver carp eggs at 330 for 2 minutes,.2 minutes after inse—
minàtion ; no diploids were produced while the normally fertilized eggs
hatehed at about 75 %.
Gynogenesis was induced in three Indian carps. Labeo rohita and Catla
catla diploids were produced with a 12€ shock ; temperatures below IDC were
lethal (John et al., 1984). John et al.
(in press) shocked Cirrhinus mrigala
eggs at 12 and 30C and reported the heat shock appeared to be more effective.
Induction of gynogenesis has many aspects needing attention. The appa—
rent
tendency for only some females to produce diploids (Stanley, 1976b ;
Tcherfas, 1971) may be related to physiological condition of the ova
than having a genetic baSis. The timing of ovulation in relation
to
insemina—
tion, or the condition of egg
ripeness at ovulation may be important.
The
optimal time of shock should be relatively narrow in relation to meiotic
events but cytological correlations are needed ; the direction, magnitude and
duration of the shock need further attention. In particular?
the
lethal
limits
Should be more thoroughly examined
to
determine the prox1m1ty of treatment
temperature. Gynogenesis and sex inversion have prov1ded a bas1s for elabo—
rating sex determination in several cyprinids ; 811
beenshown to be
homogametic in the female (table). Induced gynogeneSis
is
not
productive
enough to be considered as a mechanism for Pr0dUC1ng monosex
stoc—
king ; however, itis adequateîDPr0Vide monosex groups for sex inver31on
and
üœir use as broodstocks for breeding programs (Shelton et al., 1982
’
Shelton, in press a).
185
used cold shocks between 0 and 80 and durations from 30—90 minutes at varying
intervals after inseminâtion with an average of 13 and 22 Z,at 5 and 15 minu—
tes, respectively. One potentially significant procedure in this study was
that eggs were not
inseminated until 2 hours after stripping. Changes occur
in ova, either through delayed stripping or by holding after stripping, which
may have an effect onpolar body retentionc
Efforts with
grass
carp have been extensive as gynogenesis was the basis
of producing monosex fish for an ecological study (Stanley, 1976c,d). A total
of over 58 million eggs yielded about 45,000 diploids (Stanley, 1979) or only
about eight diploids in 10,000 eggs. My personal experience, also without
dærmalshocking, has been production of 1.8—2.2/10,000. Stanley (1976b) pro—
duced 56 diploids/10,000 eggs ; however, if only those females that produced
diploids were conàidered, production was about 300/10,000° Enhancement of
diploidization througl1thermal shocks as suggested by carp studies has been
inconsistent… Most treatments have been cold shocks with temperatures ranging
from 2—18C, durations of 15—60 minutes at assumed optimal intervals of 1—15
minutes after inseminatione Yield has been little enhanced ; usually morta—
lity was nearly complete, suggesting sensitivity to low temperatures as repor—
ted by Stott and Cross (1973). Surprisingly, few attempts have been made with
elevated temperatures, although Stanley (1979, 1981) reported moderate impro—
vement.
Near lethal levels may be required ; Frank (1974) reported that carp
eggs were killed at â2—45C in 10 minutes and Stanley (1981) found that 35C
for 5 minutes killed grass carp eggs.
Similarly, inducement of gynogenesis in silver carp (Mirza and Shelton,
in prep…) and bighead carp were most promising with heat shock° Maximum yiekk
for both species occurred at 1—5 minutes with shocks of 32—34C for 1—2 minutes
Cold shocks of 5
and 22C produced virtually no diploids. No shock controls
yielded less than 10/10,000, while optimal shock increased production by 10
times. From eight silver carp females, 1 million eggs were shocked but only
899 diploids were produced. Likewise, from four bighead carp females, 1.2
million eggs were shocked and only 224 diploids developed. Subsequently, I
shocked 630,000 silver carp eggs at 330 for 2 minutes,.2 minutes after inse—
minàtion ; no diploids were produced while the normally fertilized eggs
hatehed at about 75 %.
Gynogenesis was induced in three Indian carps. Labeo rohita and Catla
catla diploids were produced with a 12€ shock ; temperatures below IDC were
lethal (John et al., 1984). John et al.
(in press) shocked Cirrhinus mrigala
eggs at 12 and 30C and reported the heat shock appeared to be more effective.
Induction of gynogenesis has many aspects needing attention. The appa—
rent
tendency for only some females to produce diploids (Stanley, 1976b ;
Tcherfas, 1971) may be related to physiological condition of the ova
than having a genetic baSis. The timing of ovulation in relation
to
insemina—
tion, or the condition of egg
ripeness at ovulation may be important.
The
optimal time of shock should be relatively narrow in relation to meiotic
events but cytological correlations are needed ; the direction, magnitude and
duration of the shock need further attention. In particular?
the
lethal
limits
Should be more thoroughly examined
to
determine the prox1m1ty of treatment
temperature. Gynogenesis and sex inversion have prov1ded a bas1s for elabo—
rating sex determination in several cyprinids ; 811
beenshown to be
homogametic in the female (table). Induced gynogeneSis
is
not
productive
enough to be considered as a mechanism for Pr0dUC1ng monosex
stoc—
king ; however, itis adequateîDPr0Vide monosex groups for sex inver31on
and
üœir use as broodstocks for breeding programs (Shelton et al., 1982
’
Shelton, in press a).