remarks
Many cuLtivated cyprinids may be reproduced in captivity, enabting
research in methods of genetic improvement. Most of these investigations
were
carried out with the common carp. Breeding schemes investigated were
reviewed at the conference. Heterosis of growth rate and disease resistance
resuLting from crossbreeding between different strains has been demonstrated
repeatedty and is apptied in commerciaL fish tarming in IsraeL, Hungary and
the Soviet Union.
In
IsraeLi
studies the performance of the best crossbreds
exceeds that of the best strain, Dor—70, by onLy a smaLL amount
Mass
seLec—
tion did not evoke a positive response. This may, in part, be a resuLt of
inbreedino. Combining mass seLection and crossbreeding has not been adequa—
teLy investigated. FamiLy seLection may have a potentiat for genetic impro—
vement and requires investigation..
Most
of the originaL contributions concerned chromosome manipuLations,
induction of gynogenesis and potypLoidy. The techniques emptoyed invoLved
retention of the second poLar body (and not suppression of first cLeavage),
resuLting in the production of partLy heterozygous individuaLs or tripLoids
One of the aims of inducing gynogenesis is the production of inbred Lines
for crossbreèding schemes. The advantage of crossbreds between gynogenetic
inbreds over crossbreds between conventionaLLy reproduced parentaL Lines
has not been adequatety demonstrated, UncontroLted reproduction may be pre—
vented by producing aLL femaLe broods through a combination of gynogenesis
and sex reversat, or by steritization through tripLoidy. Growth and yieLds
of such non reproducing popuLations has not been compared to those of fer—
tiLe,
bi—sexuaL populations. In most investigations reported at the confe—
rence,
coLd shocks were used for restoring the temaLe dipLoid compLement.
Reported survivaL rates were much Lower than those in the cLassicaL
Hungarian studies. Heat shocks, investigated in a singLe study, resuLted in
survivaL
rates
simiLar to those demonstrated in Hungary. In investigations
in chromosome manipuLations invoLVing other cyprinids, ttke tench and
mrigaL, the shock technique was not optimized, and survivaL rates were Low.
The use of chromosome manipuLations as a means of controtting the repro—
duction of introduced exotics was reviewed. This has been demonstrated in
grass
carp.
As
in aquacuLture, monosexing invOLves gynogenesis and sex
reversaL. SteriLe tripLoids may be produced either by direct thermaL shock
or
by mating dipLoids with tetrapLoids ; but tetraptoidy has not yet been
induced in any cyprinids.
Intergeneric hybridization was investigated in Indian cyprinids. Growth
of hybrids did not exceed that of the better parent, as in many other inter—
i
generic or interspecific crosses in fishes.
In summary, different methods of seLective breeding have
been investi—
gated, but their reLative efficiencies, in terms of response per UÛIÎ
Of
effort or time, have not been compared. AvaiLabte
knowLedge is appL1ed to
commerciaL aquacuLture in onLy few countries. This appears to be also the
case
in other fishes, in addition to common carp.
i
D.
CHOURROUT and e.w. NOHLFARTH
T
Many cuLtivated cyprinids may be reproduced in captivity, enabting
research in methods of genetic improvement. Most of these investigations
were
carried out with the common carp. Breeding schemes investigated were
reviewed at the conference. Heterosis of growth rate and disease resistance
resuLting from crossbreeding between different strains has been demonstrated
repeatedty and is apptied in commerciaL fish tarming in IsraeL, Hungary and
the Soviet Union.
In
IsraeLi
studies the performance of the best crossbreds
exceeds that of the best strain, Dor—70, by onLy a smaLL amount
Mass
seLec—
tion did not evoke a positive response. This may, in part, be a resuLt of
inbreedino. Combining mass seLection and crossbreeding has not been adequa—
teLy investigated. FamiLy seLection may have a potentiat for genetic impro—
vement and requires investigation..
Most
of the originaL contributions concerned chromosome manipuLations,
induction of gynogenesis and potypLoidy. The techniques emptoyed invoLved
retention of the second poLar body (and not suppression of first cLeavage),
resuLting in the production of partLy heterozygous individuaLs or tripLoids
One of the aims of inducing gynogenesis is the production of inbred Lines
for crossbreèding schemes. The advantage of crossbreds between gynogenetic
inbreds over crossbreds between conventionaLLy reproduced parentaL Lines
has not been adequatety demonstrated, UncontroLted reproduction may be pre—
vented by producing aLL femaLe broods through a combination of gynogenesis
and sex reversat, or by steritization through tripLoidy. Growth and yieLds
of such non reproducing popuLations has not been compared to those of fer—
tiLe,
bi—sexuaL populations. In most investigations reported at the confe—
rence,
coLd shocks were used for restoring the temaLe dipLoid compLement.
Reported survivaL rates were much Lower than those in the cLassicaL
Hungarian studies. Heat shocks, investigated in a singLe study, resuLted in
survivaL
rates
simiLar to those demonstrated in Hungary. In investigations
in chromosome manipuLations invoLVing other cyprinids, ttke tench and
mrigaL, the shock technique was not optimized, and survivaL rates were Low.
The use of chromosome manipuLations as a means of controtting the repro—
duction of introduced exotics was reviewed. This has been demonstrated in
grass
carp.
As
in aquacuLture, monosexing invOLves gynogenesis and sex
reversaL. SteriLe tripLoids may be produced either by direct thermaL shock
or
by mating dipLoids with tetrapLoids ; but tetraptoidy has not yet been
induced in any cyprinids.
Intergeneric hybridization was investigated in Indian cyprinids. Growth
of hybrids did not exceed that of the better parent, as in many other inter—
i
generic or interspecific crosses in fishes.
In summary, different methods of seLective breeding have
been investi—
gated, but their reLative efficiencies, in terms of response per UÛIÎ
Of
effort or time, have not been compared. AvaiLabte
knowLedge is appL1ed to
commerciaL aquacuLture in onLy few countries. This appears to be also the
case
in other fishes, in addition to common carp.
i
D.
CHOURROUT and e.w. NOHLFARTH
T