Commercially grown tilapia are almost exclusively male, typically done by adding male sex hormone in the food to the tilapia fry, causing any potential female tilapia to change sex to male. It can also be achieved through hybridization of certain tilapia species or the use of so-called "supermales" that have homozygous male sex chromosomes (resulting in all their offspring receiving a male sex chromosome and thus becoming males). Males are preferred because they grow much faster than females. Additionally, because tilapia are prolific breeders, the presence of female tilapia results in rapidly increasing populations of small fish, rather than a stable population of harvest-size animals.