Comm! of sex in Cyprinids
183
effects. Theoptimallevel is most important if functional sex inversion is
desired, i.e. a fertile gonad that
produces gametes with a sexual genotype
different from the sexual phenotype.
Relatively few cyprinid sex inversion studies have been done and these
used two different modes of delivering methyltestosterone (MT). Yamamoto and
Kajishima (1968) succeeded in functionally sex inverting goldfish by feeding
MT
to
newly hatched fry (2 days posthatch) for 60 days. Fish were about 27 mm
TL at
the
end of treatment
and
97 % were males. The success correlates with
the
size at G.D.
Seven males were progeny tested and one had only female
offspring, confirming that
females
are
XX.
Bende
(1982) orally androgen
treated crucian carp
(Carassius auratus)from 3 days posthatch for 90 days.
Two hormone levels, MT—25 and MT—3O produced only males while MT—50 and
MT—1OO were ineffective. Two studies reported androgen treatment of common
carp.
Sathyanarayana and Satyanarayana—Rao (1983) fed MT—220 for 131 days. No
sex
inversion was indicated but all females had sterile
gonads. The hormone
level was probably too high and the duration too long. Nagy et al. (1981) fed
MT—100 to carp fry for 36 days at 20 and 25C within various age and size
groups.
Treatment effect was lower in all
groups at the cooler temperature.
Optimal treatment at 250 started with fry 8—44 days old or with fry 7—19 mm
long and terminated at 21—57 mm, respectively. G.D. is completed at about
40 mm (Davies and Takashima, 1980). Sex inversion was functional ; six males
were
bred with normal females to
produce only female offspring, indicating
that female carp
are
XX.
Sex inversion has been attempted for grass carp with two means of hormone
delivery. All attempts to sex invert grass carp by oral MT treatment failed.
Stanley and Thomas (1978) fed MT—30 or MT—60 over variable periods starting
from first feeding to 16 weeks old and for 2—9 weeks duration. None of the
fish reached a size that would have included G.D. Johnson (1972) fed MT—20
for 88 days starting at 1 month of age. His feeding period should have encom—
passed G.D. but the hormone level may have been too low. Jensen (1979) also
attempted oral treatment ; he used MT—60 and MT—120 starting with 16—week—old
fish (89—100 mm). He continued feeding for 275 days with one group and 410
days with the other. Neither treatment altered the sex ratio from I:]. even
though the entire period of G.D. was encompassed. It seems obvious that
although grass carp are sustained on a prepared diet, growth/nutrition are
apparently insufficient to develop an effective androgen exposure.
Concomitantly, an alternate means of delivery was developed using an_ùnplantfabricated
from si1astic tubing packed with 12—mg of MT. The carrier was
placed in the body cavity of fingerling grass carp andthen stocked in ponds
for 192 and 305 days. Five fish developed ovotestes and the others had redu—
ced germ cell development (Jensen et al., 1978). Subsequent treatment was
modified to include growth management through stocking density (Shelton et
al., 1981)
;
about 50 % were sex inverted when implantedat 124—134 mm and
stocked at about 4000/ha (Jensen et al., 1983). In later trials, a smaller
implant (5—mg) was used and treatment was initiated with 80-105 mm fish, 10—16
weeks of age and stocked at 50—2500/ha ; 88 % Of implanted
flSh were sex
inverted (Boney et al., 1984). In this study an 1n3ectable carrier was
also
tested but the results were not encouraging- Subsequent stock1ng den31ty
trials
more
clearly defined optimal rates for treatment (Rosenblatt, 1982).
Growth management was used in nursing the grass carp to the appropriate
implantation size and to control growth during treatment ln ponds ln order
Io attain the size at which G.D. was complete. Grass carp were spawned in May,
nursed to
about
100 mm for treatment amd restocked between 1750 and 7000/ha ;
bY the end of the growing season they were larger than 160-180 mm and
had occured.
Sex inversion of grass carp was not successful until information
On G.D. was available and the androgen treatment was taYlored t° dellV€ï_an
adequate level during G.D. Breedin8
grass carp males
(genetic
females) has produced only females, substant1at1ng that female grass carp are
XX (Shelton, in press a).
183
effects. Theoptimallevel is most important if functional sex inversion is
desired, i.e. a fertile gonad that
produces gametes with a sexual genotype
different from the sexual phenotype.
Relatively few cyprinid sex inversion studies have been done and these
used two different modes of delivering methyltestosterone (MT). Yamamoto and
Kajishima (1968) succeeded in functionally sex inverting goldfish by feeding
MT
to
newly hatched fry (2 days posthatch) for 60 days. Fish were about 27 mm
TL at
the
end of treatment
and
97 % were males. The success correlates with
the
size at G.D.
Seven males were progeny tested and one had only female
offspring, confirming that
females
are
XX.
Bende
(1982) orally androgen
treated crucian carp
(Carassius auratus)from 3 days posthatch for 90 days.
Two hormone levels, MT—25 and MT—3O produced only males while MT—50 and
MT—1OO were ineffective. Two studies reported androgen treatment of common
carp.
Sathyanarayana and Satyanarayana—Rao (1983) fed MT—220 for 131 days. No
sex
inversion was indicated but all females had sterile
gonads. The hormone
level was probably too high and the duration too long. Nagy et al. (1981) fed
MT—100 to carp fry for 36 days at 20 and 25C within various age and size
groups.
Treatment effect was lower in all
groups at the cooler temperature.
Optimal treatment at 250 started with fry 8—44 days old or with fry 7—19 mm
long and terminated at 21—57 mm, respectively. G.D. is completed at about
40 mm (Davies and Takashima, 1980). Sex inversion was functional ; six males
were
bred with normal females to
produce only female offspring, indicating
that female carp
are
XX.
Sex inversion has been attempted for grass carp with two means of hormone
delivery. All attempts to sex invert grass carp by oral MT treatment failed.
Stanley and Thomas (1978) fed MT—30 or MT—60 over variable periods starting
from first feeding to 16 weeks old and for 2—9 weeks duration. None of the
fish reached a size that would have included G.D. Johnson (1972) fed MT—20
for 88 days starting at 1 month of age. His feeding period should have encom—
passed G.D. but the hormone level may have been too low. Jensen (1979) also
attempted oral treatment ; he used MT—60 and MT—120 starting with 16—week—old
fish (89—100 mm). He continued feeding for 275 days with one group and 410
days with the other. Neither treatment altered the sex ratio from I:]. even
though the entire period of G.D. was encompassed. It seems obvious that
although grass carp are sustained on a prepared diet, growth/nutrition are
apparently insufficient to develop an effective androgen exposure.
Concomitantly, an alternate means of delivery was developed using an_ùnplantfabricated
from si1astic tubing packed with 12—mg of MT. The carrier was
placed in the body cavity of fingerling grass carp andthen stocked in ponds
for 192 and 305 days. Five fish developed ovotestes and the others had redu—
ced germ cell development (Jensen et al., 1978). Subsequent treatment was
modified to include growth management through stocking density (Shelton et
al., 1981)
;
about 50 % were sex inverted when implantedat 124—134 mm and
stocked at about 4000/ha (Jensen et al., 1983). In later trials, a smaller
implant (5—mg) was used and treatment was initiated with 80-105 mm fish, 10—16
weeks of age and stocked at 50—2500/ha ; 88 % Of implanted
flSh were sex
inverted (Boney et al., 1984). In this study an 1n3ectable carrier was
also
tested but the results were not encouraging- Subsequent stock1ng den31ty
trials
more
clearly defined optimal rates for treatment (Rosenblatt, 1982).
Growth management was used in nursing the grass carp to the appropriate
implantation size and to control growth during treatment ln ponds ln order
Io attain the size at which G.D. was complete. Grass carp were spawned in May,
nursed to
about
100 mm for treatment amd restocked between 1750 and 7000/ha ;
bY the end of the growing season they were larger than 160-180 mm and
had occured.
Sex inversion of grass carp was not successful until information
On G.D. was available and the androgen treatment was taYlored t° dellV€ï_an
adequate level during G.D. Breedin8
grass carp males
(genetic
females) has produced only females, substant1at1ng that female grass carp are
XX (Shelton, in press a).