Control of sex in Cyprinids
187
reported differences between initial stripping and delayed egg collection ;
viability was reduced from 16 to 3 % but triploidy increased from 33 to 100 %
in the eggs that were stripped 50 minutes late.
A similar phenomenon to triploid induction involves interspecific hybri—
dization. Hybrids between closely related species often produce viable and
fertile offsprings (Chevassus,
1983). In reciprocal hybrids between silver
and bighead carp, batch rate was as high or higher than with the intras—
pecific parental cross (Shelton, unpub.
data)° These fish were growth tested
in two consecutive years
(Green and Smitherman, 1984). However, more distantly
related species such as grass carp and bighead carp have reduced viability
of
the hybrid Offspring (Bakos et al., 1978) which may result in gynogenetic
progeny
(Andria5heva, 1967 ; Makeyeva, 1975) or survival of predominately
triploids or both (Marian and Krasznai,
Survival of progeny from this
cross
included 70—85 % malformed individuals which died within 12—14 days of
hatching. The survivors were primarily triploid but with some gynogenetic
and a few diploid hybrids° Triploids have one—half of the paternal complement,
but
the
total maternal genome which imparts an increased survival to an other—
wise low compatibility cross… The triploid grass carp reported by Marian and
Krasnai
(1978) was well received as a potentially sterile, weedeating fish ;
Sutton et
al.
(1981) summarized the history of this hybrid and its potential
in the U.S.
Efforts
to
increase triploidization paralleled gynogenetic induc—
tion as the key is retention of the polar body ; Chevassus et al.
(1983)
discussed similar induction with salmonid hybridsc Biologists of the Florida
Freshwater Fish Commission heat and cold shocked eggs to increase triploid
hybrid production ; no combination that they tested greatly enhanced the yield
and after numerous
tests
of weed control effectiveness, interest has largely
been directed toward the triploid grass carp. Triploid grass carp are now
being marketed in the U.S. but specifics of production are proprietary and
can
only be surmised° However… production does require culling from the
mixture of individuals with different ploidy.
INTEGRATION OF TECHNIQUES.(Îigure in next page).
Comprehensive management for limited reproductivity in fish is achie—
vable by integrating appropriate techniques. Gynogenesis in cyprinids provides
an
all—female group
that
can
be
androgen treated to produce male broodstock.
Breeding sex—inverted males with normal females should produce only female
progeny and replacement male broOdstock can be produced by androgen treating
the required number of progeny. Such a program has been developed for grass
carp
(Shelton, in press a) and is presently being used (Freeze, 1983). Simi—
larly, the breeding program for common carp in Hungary used this protocol
(Nagy and Csanyi, 1984). The use of this approach to prevent potential natura—
lization of exotic fishes can only be functional if developed prior to introduction (Shelton, in press b). The following figure depicts the program and
its possible extension to polyploidization and large developing method to
induce fertile tetraploids (Bidwell et al. in press) reported the induction
of tetraploids in 62 % of the viable larvae of channel catfish (Ictalurus
punctatus). Comparable success with rainbow trout (Chourrout, 1982, 1984)
the
development can be achieved. With & PÏOËOC01 Of thl$
nature
reproductively limited populations of fish can be produced on
a
practical
scale with induced gynogenesis, sex inversion and polyploldlzatlon only be1ng
needed to produce broodstock.
187
reported differences between initial stripping and delayed egg collection ;
viability was reduced from 16 to 3 % but triploidy increased from 33 to 100 %
in the eggs that were stripped 50 minutes late.
A similar phenomenon to triploid induction involves interspecific hybri—
dization. Hybrids between closely related species often produce viable and
fertile offsprings (Chevassus,
1983). In reciprocal hybrids between silver
and bighead carp, batch rate was as high or higher than with the intras—
pecific parental cross (Shelton, unpub.
data)° These fish were growth tested
in two consecutive years
(Green and Smitherman, 1984). However, more distantly
related species such as grass carp and bighead carp have reduced viability
of
the hybrid Offspring (Bakos et al., 1978) which may result in gynogenetic
progeny
(Andria5heva, 1967 ; Makeyeva, 1975) or survival of predominately
triploids or both (Marian and Krasznai,
Survival of progeny from this
cross
included 70—85 % malformed individuals which died within 12—14 days of
hatching. The survivors were primarily triploid but with some gynogenetic
and a few diploid hybrids° Triploids have one—half of the paternal complement,
but
the
total maternal genome which imparts an increased survival to an other—
wise low compatibility cross… The triploid grass carp reported by Marian and
Krasnai
(1978) was well received as a potentially sterile, weedeating fish ;
Sutton et
al.
(1981) summarized the history of this hybrid and its potential
in the U.S.
Efforts
to
increase triploidization paralleled gynogenetic induc—
tion as the key is retention of the polar body ; Chevassus et al.
(1983)
discussed similar induction with salmonid hybridsc Biologists of the Florida
Freshwater Fish Commission heat and cold shocked eggs to increase triploid
hybrid production ; no combination that they tested greatly enhanced the yield
and after numerous
tests
of weed control effectiveness, interest has largely
been directed toward the triploid grass carp. Triploid grass carp are now
being marketed in the U.S. but specifics of production are proprietary and
can
only be surmised° However… production does require culling from the
mixture of individuals with different ploidy.
INTEGRATION OF TECHNIQUES.(Îigure in next page).
Comprehensive management for limited reproductivity in fish is achie—
vable by integrating appropriate techniques. Gynogenesis in cyprinids provides
an
all—female group
that
can
be
androgen treated to produce male broodstock.
Breeding sex—inverted males with normal females should produce only female
progeny and replacement male broOdstock can be produced by androgen treating
the required number of progeny. Such a program has been developed for grass
carp
(Shelton, in press a) and is presently being used (Freeze, 1983). Simi—
larly, the breeding program for common carp in Hungary used this protocol
(Nagy and Csanyi, 1984). The use of this approach to prevent potential natura—
lization of exotic fishes can only be functional if developed prior to introduction (Shelton, in press b). The following figure depicts the program and
its possible extension to polyploidization and large developing method to
induce fertile tetraploids (Bidwell et al. in press) reported the induction
of tetraploids in 62 % of the viable larvae of channel catfish (Ictalurus
punctatus). Comparable success with rainbow trout (Chourrout, 1982, 1984)
the
development can be achieved. With & PÏOËOC01 Of thl$
nature
reproductively limited populations of fish can be produced on
a
practical
scale with induced gynogenesis, sex inversion and polyploldlzatlon only be1ng
needed to produce broodstock.