7. POLY CULTURE OF AFRICAN CATFISH AND NILE TILAPIA

Nile Tilapia (Oreochromis niloticus) is the most important species farmed in the African countries. A disadvantage of the farming of the Nile Tilapia is its excessive reproduction and at harvest 23% of the biomass consists of fingerlings⁷ (see figure 6). The major problem with the existence of the fingerling is the fact that they consume the feed which is provided for the adult Tilapia and consequently the growth rate of the adults is reduced. The number of fingerlings at harvest can be reduced by rearing the Nile Tilapia in combination with a predator. In Africa the following predator are used in poly culture with the Nile Tilapia;

• Clarias gariepinus; It is a “lazy” predator but it works well as long as they are stocked in high densities.
• Ophiocephalus obscuris; It is a highly effective predator as it is completely piscivorous.
• Hemichromis fasciatus: It is a good predator but its market value is low and it is rather fragile so high mortalities are occurring at harvest.
• Lates niloticus: Is a good predator but it is difficult to obtain fingerlings.

⁷ In a mixed culture, a rearing cycle of 6 month and wheat bran as feed.

The African catfish must be stocked in high densities in order to obtain a complete reduction of the Tilapia fingerlings, as it prefers to feed on the supplied feed. In general the ponds are stocked with 2 Tilapia per square meter and with 1 Catfish per square meter. The fish can be fed all kinds of agriculture by products as; rice bran, wheat bran, cotton seed cake, etc The feeding rate must be adjusted to the presence of the catfish as otherwise all fish are underfed. In practice for the monthly adjustment of the feeding rate the weight of the catfish is considered to be the same as the weight of the Tilapia.

Large scale poly culture of Tilapia-Catfish executed in Congo Brazzaville indicated that “small” catfish with a weight less as 7 grams can not erase completely the fingerlings. The reason is that the African catfish becomes piscivorous at a weight of 7–10 gram, consequently all Nile Tilapia larvae born in the beginning of the rearing period escape predation. From a practical point of view this is a advantage as at harvest a small number of nicely calibrated fingerlings (30–35 gram) are obtained.

Some parameters of polyculture Nile Tilapia/African catfish is presented in Table 2 and more details can be found in Annex 2.

Table 2: Key parameters of poly culture of Nile Tilapia with African Catfish