Appropriate stocking of the pond

Depending on the available feeding resources, 2 to 4 fish per m² of pond area are appropriate with a sex ratio of one male per 4 to 5 females. The male fish should weigh 200 to 300 grams, the females 700 grams or more.

In most Orechromis species, the male fish grow bigger and faster than the female fish. This is one reason why it is recommended to work with just one sex per pond. Another reason is that mixed populations will propagate very early in the pond leading to what is called stunning of the production. The juveniles and fingerlings will compete for the feed with the adult fish, which will result in much smaller fish. If only males are grown, the female fish are either culled after sexing or raised separately in another pond.

In organic pond farming, there are two possibilities to obtain very high rates of one sex:

• The first one is to cross two different tilapia species to obtain hybrids. If a particular species is used, the offspring can be up to 100 % males. One example is to mate female Orechromis mossambicus with male Oreochromis urolepis hornorum to achieve what is known as Malacca hybrid.
• The second possibility is the selection of the fingerlings manually by checking their genital papilla, when the fish are about 10 cm in size. At this size, Nile tilapia can be differentiated on the basis of the genital papilla. This is very labour-intensive and requires some experience, but has the advantage that the farmer does not need to keep different species as brood stock.

If the farm fish production relies on purchased fingerlings from hatcheries, the farmer must make sure that the tilapias (especially Orechromis species) were not given any hormones. Hormonal treatment is not allowed in certified organic farming. Hormones are commonly fed to produce male fish only, as male fish, especially in tilapia, tend to grow bigger and faster than females. If the farmer cannot buy mono-sex fingerlings that are guaranteed not to have had hormonal treatment in the past, he would need to buy mixed sexes or run his own breeding.

A good way to control unwanted juveniles in the pond is to put some predator fish in the pond (for example, African catfish Clarias gariepinus or snake head Ophiocepalus spp.). The predator fish shall not be bigger than double the size of the smallest tilapia. No more than five percent of the entire fish stock in a pond should be predator fish. For example: if the farmer has a ’standard pond’ of 100 m² (10 m x 10 m), the farmer can stock it with 200 to 400 fish in the beginning, depending on his external feed availability. That means at low stocking density (with little or without external feeding) he can put 190 tilapia fingerlings of 10 to 12 cm and 10 catfish or snakehead fish of about 20 cm into the pond, or 380 tilapia and 20 prey fish, if he chooses to have high stocking density (and has the possibility for sufficient external feeding).