The Influence of Various Feeding and Pond Fertilization Strategies on Nile Tilapia (Oreochromis niloticus L.) Production and the Selectivity for Natural Versus Supplementary Diet in Semi-Intensive Aquaculture Systems

High feed costs constrain tilapia production, making exploring low-cost feeding strategies important. We assessed the growth of tilapia over a period of 6 months, fed 1%, 2%, or 4% of body mass day⁻¹ with and without fertilization in 18 liner ponds stocked with fingerlings (5.1 ± 0.71 g). Growth was significantly better in fertilized ponds than in unfertilized ponds. The best growth (320.7 ± 8.5 g) was in fertilized ponds where fish were fed 2%, achieving a 45% larger weight gain than in the group fed 4% in unfertilized ponds. These results show that with fertilization, the feeding can be reduced by half while still having better growth than in unfertilized ponds. In fertilized ponds fed 4%, the minimum nocturnal oxygen levels may have limited growth of the fish and, as a result, their final weight (180.1 ± 6.6 g) was lower than in groups fed 2% in fertilized ponds and 4% in unfertilized ponds. Fish up to 60–90 g rely mainly on zooplankton as a source of food, while fish of sizes ≥100 g rely mainly on supplementary feed. Analysis of the gut content of fish of different sizes suggested that tilapia up to 60–90 g do not consume the feed presented which instead ends up as an expensive form of fertilizer. The best economic return was in ponds that were fertilized and fed 2%. It is concluded that feed-use and production costs may be reduced even further by fertilizing the ponds and restricting or omitting feeding of fish < 100 g and only commence feeding when the fish have reached around 100 g. The results of the finding have a wider applicability in developing countries where pond culture of tilapia is common.