How are GMT® produced?
Through the application of relatively simple genetic manipulations, the University of Wales Swansea and its collaborators have developed an innovative and robust new genetic technology for producing all- or nearly all-male progeny in the Nile tilapia (Mair et al, 1997). Known as the "YY male technology" this takes the form of a breeding programme combining feminization and progeny testing, to produce novel males with YY genotypes (i.e. with 2 male sex chromosomes) instead of the usual XY male genotype. These YY males are known as "supermales" and have the unique property of siring only genetically male progeny. These progeny are termed genetically male tilapia (GMT®) and are normal males (although some can "naturally" revert to female, giving GMT® an average sex ratio of >95% male).
It is important to understand that no genetic engineering techniques are used in the development or production of GMT, just basic breeding. GMT® are not genetically modified organisms (GMOs) and the on-going debate about genetically modified foods does not apply to GMT®. The hormone treatments used as part of the process to produce YY males are two generations removed from the fish that are consumed so neither the GMT® or their YY male parents are treated in any way, making the technology safer than hormonal sex reversal. This is an environmentally friendly technology, which requires no special facilities for application.