Ponds with professionally made impermeable liners are too expensive at the smallest scale of pond fish culture. For such farmers, soils that hold water are essential. The easiest way to check if the local soil has suitable water holding capacity is to dig a hole, perhaps one metre in volume, fill it with water and leave it overnight. If there is no water left in the morning, a source of clay will have to be found with which to plaster the sides of the finished pond. The siting and shape of the pond is also important.
Rectangular ponds are easier to manage and seem also to be better for wind and water circulation.
This helps to aerate the water and stir up the nutrients making them more readily available to the fish. The bottom of the pond is usually made to slope so that, when harvested, most of the water can be drained out and the mature fish can be harvested, leaving the young fry for re-stocking. There are disadvantages to this method of re-stocking because farmers naturally remove the largest or fastest growing fish from the pond and put back the smallest or slowest growing ones. The result is that the genes for slow growth are passed on to the next generations. To prevent this, a new stock of fish should be brought in from time to time.