Frequently Asked Questions
GMT® stand for?
can I obtain GMT®?
GMT® a product of
is a "supermale"?
I produce GMT®
in my own hatchery?
I need any special facilities to produce or grow
you have red
is the difference between
and sex reversed tilapia?
grow well in brackish water?
does GMT® stand for?
GMT® is a registered trademark and acronym for Genetically
and refers to progeny from YY "supermales". When crossed to
females these supermales produce only XY male progeny. The properties of
GMT® are derived from the fact that they represent populations made up of ONLY
genetically male progeny. Each individual
GMT® is a normal genetic male (XY). The superior properties of
GMT® are a function of the whole population being genetically male,
obviating the problems of inferior growth of females, diversion of energy
to reproduction and the production of unwanted fry and fingerlings.
How can I obtain
GMT® can be purchased directly from Fishgen or from one of our
agents located worldwide. Contact Fishgen
for a quotation stating your location and the approximate number of
would like to purchase. It would also be useful if you could provide brief
details of your production system.
product of genetic engineering?
Genetic engineering commonly involves techniques that
manipulate genes in ways that bypass normal sexual reproduction, such as the
introduction of novel genes through transgenesis. The products of genetic
engineering are often referred to as Genetically Modified Organisms (GMOs). GMT®
are produced in a simple breeding programme combining sex reversal and
progeny testing which does not involve any genetic engineering techniques.
GMT® are thus little different to fish produced from normal crosses
selection programmes and are not considered as GMOs according to legal standard definitions.
What is a supermale?
A supermale is a male which has the novel YY genotype, possessing two male sex
determining chromosomes instead of one, as in the normal, naturally occurring
male genotype (XY). Supermales themselves, are not hormonally or otherwise
treated in any way. In the Fishgen technology, supermales (YY) are crossed to normal females (XX) to
GMT® (XY). Supermales have been produced in a number of fish
species but are normally inviable in higher organisms such as humans.
GMT® in my own hatchery?
You can produce
GMT® in your own hatchery by purchasing
GMT® producing broodstock from Fishgen. We supply
GMT® producing broodstock as sets (each set includes 1 YY
male and 3 females). Contact Fishgen
for a quotation for
GMT® producing broodstock indicating your location and the number
of broodstock sets you might require (or alternatively, your targeted fingerling
production). GMT® producing broodstock are not available in
some locations due to commercial restrictions.
Do I need any
special facilities to produce or grow
No, as normal genetic males GMT® require
no special treatment or facilities. GMT® producing
broodstock can be used successfully in a wide range of commercial hatchery systems
and likewise the benefits of GMT® can be seen in all grow-out
systems. We do, however, recommend that all efforts are taken to prevent
contamination of YY males with any normal males in hatchery systems.
Similarly, efforts should be made to ensure that females don't contaminate GMT® in grow-out
systems. This can be achieved by draining systems before stocking and by careful
screening of inlet and outlets. We recommend the tagging of YY males in
hatcheries although this is not required.
Can I use
As stated above, GMT® are normal fertile
males and can be used as broodstock. However, use
of GMT® as male broodstock, crossed with normal females, will
produce normal mixed sex progeny so there is little advantage to
this. GMT® themselves can only be produced as progeny of
Do you have red
Fishgen has been developing a GMT® in a
red strain of pure O. niloticus. This red GMT® should
be available by the second half of 2002.
How fast do
The short answer to this question is that it depends on
the conditions in which you grow them. We cannot accurately predict the
growth rate of GMT® in any particular system but we do know, based
on extensive growth trials, that GMT® have outperformed
comparable tilapia in a wide range of production systems.
What is the difference
GMT® and sex reversed tilapia?
As stated above, GMT® are normal male
tilapia and are not GMOs. Sex reversed tilapia (SRT) are
all-male progeny, produced through direct oral administration of male hormone
during the period of sexual differentiation. Approximately 50% of SRT
remain as genetic females although phenotypically male. The advantages of GMT®
over SRT include: