The commonly farmed mouth-brooding tilapias are normally highly prolific. This might sound like a good thing for a farmer, but it can actually turn into a serious problem. Space and food are both limited resources and forcing adult fish to compete with fry and fingerlings can lead to a reduced growth rate or even stunting.  

One way of preventing the problem with numerous fry and fingerlings is to avoid keeping male and female tilapias together. Males grow bigger than females when it comes to tilapia and are therefore normally the sex of choice for mono-sex cultures.

Batches of young mono-sex tilapia can be obtained from tilapia breeders that utilize various techniques to achieve a skewed sex ratio in their fish. The two most commonly used techniques are hybridization and hormones.

When certain species or strains of tilapia breed with each other the resulting batch of hybrids consist of a very low number of females or no females at all. (The presence of females is often caused by the presence of foreign genetic material.) Breeding a Nile tilapia female (Oreochromis nilotica) with a Blue tilapia (Oreochromis aurea) or Zanzibar tilapia (Oreochromis hornorum) male is one popular alternative, and so is crossing a Mozambique tilapia (Oreochromis mossambicus) female with any of the above mentioned males.

Hormone treatment is an efficient method of making female offspring turn into male offspring, but it is important to keep in mind that the use of hormones in fish farms is restricted or even prohibited in several parts of the world. There is also always the risk of certain consumer groups reacting badly to what they perceive as an unnecessary use of hormones in their food.