Induction of gynogenesis in
the turbot (Scophthalmus maximus):
Effects of UV irradiation on
sperm motility, the Hertwig effect and viability during the first 6 months
of age
F. Piferrer, R.M. Cal, C. Gómez, B. Álvarez-Blázquez,
J. Castro, P. Martínez-2004
Aquaculture, 238: 403-419
Abstract:
Fish in which gynogenesis has been induced have all
their chromosomes inherited from the mother and, if females are the
homogametic sex, they usually are all females. Because turbot females grow
faster than males, the production of all-female populations is highly
desirable. The sperm of turbot is of poor quality and its larvae are small
and fragile. These circumstances represent a challenge for the induction of
gynogenesis in the turbot. As a first step towards this goal, effective
conditions for the induction of gynogenesis through UV irradiation of sperm
followed by a cold shock were established. When diluted 1:10 with Ringer-200
saline solution and placed in a thin layer (~0.3 mm), a dose-dependent
effect of UV light on sperm motility was found. The dose at which both the
amount of motile sperm and the duration of sperm motility was reduced to 50%
of the original value (ID50) was ~28,000 erg mm−2.
A typical Hertwig effect was elicited with a dose of 30,000 erg mm−2.
The resulting embryos exhibited the typical "haploid syndrome" and
died shortly after hatching. Application of a cold shock (−1 to 0°C
for 25 min starting at 6.5 min after fertilization) to activated eggs with
UV-irradiated (30,000 erg mm−2) and diluted (1:10) sperms
restored diploidy and resulted in the production of gynogenetic diploids (2n=44
chromosomes). These conditions were used in a pilot-scale experiment and
found effective in inducing gynogenesis in ~47,000 eggs. The rate of
gynogenesis induction was 100% as verified by an analysis with
microsatellite DNA markers. Survival of the gynogenetics was approximately
10% of diploids at 6 months of age, although growth was similar during this
period. If this species turns out to have female homogamety, as is the case
in most pleuronectiformes examined so far, the method presented here is the
first necessary step for the production of all-female populations of this
economically important species.
(Institut de Ciències del Mar, Consejo Superior de
Investigaciones Científicas (CSIC), Passeig Marítim, 37-49, 08003,
Barcelona, Spain, e-mail: piferrer@icm.csic.es)