Tilapias are native to Africa mostly. They occur as far north as the Sea of Galilee.
Their claim to fame is that they can survive in low-oxygen water (by gulping air like some other fish do as well), happen to be herbivorous or at least compatible with being herbivorous (quite rare in fish--big fish usually eat little fish), and are either mouth-brooders or nesters.
The reason those traits are significant is because they result in Tilapias being amenable to tanks, "low-trophic" (you can feed them vegetable garden leftovers--as well as feed them other stuff a certain member of this board objects to), and they are easy to breed in tanks unlike most fish. Apparently a little too easy--they tend to overpopulate quickly and you have to "harvest" them accordingly.
But wait, it gets even better! Being typically natives of stagnant-water lakes, they have high tolerance to brackish water.
For all these reasons they are one of the most popular fish-farm fish in the world.
One big problem: they are warm-water fish. Unless you live in the subtropics or tropics your tank or pond will get too cold in the winter without some source of artificial heat. One possibility, if you have a big greenhouse that stays warm, is to have tanks in your greenhouse. In that case, pump their dirty water through the roots of hydroponically-grown tomatoes, cucumbers, melons, peppers, and so on. The nitrates will feed the vegetables.
