180
WL. Shafäon
INTRODUCTION.
Reproductive control may imply management of spawning to enhance seed
production, or conversely, to eliminate the production of unwanted progeny.
In the context
of
the present discussion, emphasis is on producing reproduc—
tively limited populations but management of ovulation is important so asto
have necessary control over timing of developmental
In the culture(
many species, induced ovulation is required to produce seed stock, yet in
other cases,
grow—out conditions meet the reproductive requirements and wild
spawning may occur, decreasing the efficiency of the growth phase. Further,
for exotic fishes, control over reproduction may be desirable if access to
natural waters is anticipatedc
Sex
control may provide other benefits to aquaculture, such as enhanced
growth from elimination of progeny related competition, by diversion of
energy into somatic growth rather than gonadal development or through genetic
improvements that are more efficiently developed using the techniques of
reproductive manipulation. Accomplishments have been considerable with non—
cyprinids and selected literature is discussed as applicable to carps. Some
approaches to reproductive control are not included as the emphasis is on
those that have genetic bases or that may be precursors to genetic applica—
tion.
Sex control by means of steroid sex inversion, gynogenesis and polyploidization have been examined separately for various species ; yet, optimal
management can be realized by a
combination of one or more of these approa—
ches.
The thesis of my discussion will involve separate characterization
of
these topics but with consideration for their integrati0n
where appro—
priate, The orientation of this symposium is directed toward fish culture,
thus the techniques should have a practical level of application ; while
many are potentially applicable, considerable improvement is needed to bring
them to the level of pragmatic utility.
GENERAL CONSIDERAÏIONS.
The primary manipulations under consideration include control of sexual
phenotype and ploidy and the application of these
to
the production of
reproductively limited populations° Reproductive control may be a result of
the population being monosexysterile or both and attainment may be throu8h
direct production or by breeding of developedhroodstock. In practice, the
direct approach may be less desirable than those using a breeding protocol.
Direct
inducement of monosex populations through sex inversion or sterile
triploid populations may be plagued by inconsistent success ; thus, the
broodstock development may be more arduous and complicated, but assuming the
infallability Of a genetic foundation, uniform production at practical
levels
may be expected.
Induced Spawning.
Control
of the ovulation process is critical to the success of various
sex
manipulations. Pullin and Kuo (1981) and Donaldson and Hunter (1983)
rev1ewed induced spawning of cultured fish. Rothbard (1981) reported techniques
for spawning common carp (Cyprinus carpio) and the Chinese carpS
and
Lam
(1982) summarized the
the Indian carps.
Ovulation
of
carps
outside the normal spawning season may be useful ; Huisman (1981)
described early SPawning through environmental manipulation and Jalabert et
_
al°
(1977) suggested an alternative gonadotropic material for spawning at low”
er
than normal temperatures. Since ovulation separates the ova from the
females physiological support system, stripping should follow Within a
reasonable period. Greater latitude is apparemtly available with salmonids
than for warmwater
fishes.
Rainbow trout (Salmo gairdneri) eggs
Could be
retained in the body cavity for several days before they—hadreduced Viability
(Cra1k and Harvey, 1984 ; Springate et al., 1984). In constrast, the delay
°f even a few hours in
Stripping CârP eggs greatly affects viability. H0rVath
(1978) developed a
schedule for common carp and the Chinese
WL. Shafäon
INTRODUCTION.
Reproductive control may imply management of spawning to enhance seed
production, or conversely, to eliminate the production of unwanted progeny.
In the context
of
the present discussion, emphasis is on producing reproduc—
tively limited populations but management of ovulation is important so asto
have necessary control over timing of developmental
In the culture(
many species, induced ovulation is required to produce seed stock, yet in
other cases,
grow—out conditions meet the reproductive requirements and wild
spawning may occur, decreasing the efficiency of the growth phase. Further,
for exotic fishes, control over reproduction may be desirable if access to
natural waters is anticipatedc
Sex
control may provide other benefits to aquaculture, such as enhanced
growth from elimination of progeny related competition, by diversion of
energy into somatic growth rather than gonadal development or through genetic
improvements that are more efficiently developed using the techniques of
reproductive manipulation. Accomplishments have been considerable with non—
cyprinids and selected literature is discussed as applicable to carps. Some
approaches to reproductive control are not included as the emphasis is on
those that have genetic bases or that may be precursors to genetic applica—
tion.
Sex control by means of steroid sex inversion, gynogenesis and polyploidization have been examined separately for various species ; yet, optimal
management can be realized by a
combination of one or more of these approa—
ches.
The thesis of my discussion will involve separate characterization
of
these topics but with consideration for their integrati0n
where appro—
priate, The orientation of this symposium is directed toward fish culture,
thus the techniques should have a practical level of application ; while
many are potentially applicable, considerable improvement is needed to bring
them to the level of pragmatic utility.
GENERAL CONSIDERAÏIONS.
The primary manipulations under consideration include control of sexual
phenotype and ploidy and the application of these
to
the production of
reproductively limited populations° Reproductive control may be a result of
the population being monosexysterile or both and attainment may be throu8h
direct production or by breeding of developedhroodstock. In practice, the
direct approach may be less desirable than those using a breeding protocol.
Direct
inducement of monosex populations through sex inversion or sterile
triploid populations may be plagued by inconsistent success ; thus, the
broodstock development may be more arduous and complicated, but assuming the
infallability Of a genetic foundation, uniform production at practical
levels
may be expected.
Induced Spawning.
Control
of the ovulation process is critical to the success of various
sex
manipulations. Pullin and Kuo (1981) and Donaldson and Hunter (1983)
rev1ewed induced spawning of cultured fish. Rothbard (1981) reported techniques
for spawning common carp (Cyprinus carpio) and the Chinese carpS
and
Lam
(1982) summarized the
the Indian carps.
Ovulation
of
carps
outside the normal spawning season may be useful ; Huisman (1981)
described early SPawning through environmental manipulation and Jalabert et
_
al°
(1977) suggested an alternative gonadotropic material for spawning at low”
er
than normal temperatures. Since ovulation separates the ova from the
females physiological support system, stripping should follow Within a
reasonable period. Greater latitude is apparemtly available with salmonids
than for warmwater
fishes.
Rainbow trout (Salmo gairdneri) eggs
Could be
retained in the body cavity for several days before they—hadreduced Viability
(Cra1k and Harvey, 1984 ; Springate et al., 1984). In constrast, the delay
°f even a few hours in
Stripping CârP eggs greatly affects viability. H0rVath
(1978) developed a
schedule for common carp and the Chinese