Aquaculture Feed and Fertilizer Resources Information System

Nile tilapia - Fertilizers and fertilization

In general, tilapias can efficiently utilize natural food and yields of 3 000 kg per hectare can be sustained in well-fertilized ponds without any supplemental feed.  This feeding strategy depends on the application of inorganic and/or organic fertilizers to stimulate the production of live food organisms and plants in the culture system and is typical of extensive and semi-intensive tilapia farming systems.  In the case of Nile tilapia culture, the production of phytoplankton should be the primary target.

The success of a pond fertilization strategy depends on the initial drying, tilling and liming of the pond substratum (Figure 8).  The drying out period to allow for adequate mud mineralization is usually between 5 to 10 days.  After drying, the pond bottom should be limed to reduce acidity/to increase pH and to ensure that the culture water has a pH of about seven-eight.  This will allow the tilapia culture ponds to respond optimally to fertilization. The total alkalinity of the water should be above 20 mg/l. A suggested liming rate for ponds based on pH and soil texture is given in Table 4.

A comprehensive review of pond fertilization and its effect on productivity and fish harvest can be found in Tacon (1988). Both chemical and organic fertilizers act by directly stimulating phytoplankton production within the pond. Inorganic fertilizers act through the primary production of the pond while organic manures can, in addition, directly stimulate higher trophic levels supplying organic matters and detritus. Organic manures are particularly suitable for tilapia culture: beyond their value as fertilizer, they represent an immediate source of food as this species can feed on detritus and plant by-products.

Pond fertilization strategies are locality dependent. Many factors determine the success of a fertilization regimen. The most important of these are soil type, water quality, species cultured and the type, application method and rate of fertilizers used and all must be carefully considered. Despite the lack of a standardized protocol of pond fertilization, the effectiveness of any program can be easily monitored by measuring the turbidity of the pond water by means of a Secchi disk, on the assumption that the main source of turbidity within the pond comes from phytoplankton population.  It has been recommended that a Secchi disk visibility of about 30 cm is optimal to achieve and maintain proper fertilization. Water exchange rate should preferably be around 5% per day.

The elemental composition of the major organic fertilizers and inorganic fertilizers used in aquaculture is summarized in Table 5 and Table 6. The first limiting nutrients affecting phytoplankton productivity in ponds are phosphate (P) and nitrogen (N). Inorganic fertilizers are commercially available and are generally based primarily on one major element and the correct combination of fertilizers is needed to optimally stimulate plankton productivity. As a general rule, three to five times less P than N should be added to culture ponds. Organic fertilizers or manure include all plant and animal materials and their fertilizer value is dependent primarily upon its carbon (C), N, P and potassium (K) content. Common organic fertilizers used in aquaculture are poultry, cow and pig dung but cottonseed meal, rice straw and other agricultural waste products can also be used.

Inorganic fertilizers are usually applied on a weekly or bi-weekly basis. Raising the frequency will lower the risk of sudden phytoplankton blooms, leading to low DO levels. Fertilizers should be applied to supply 0.5 – 1 mg/l of nitrogen and 0.1 – 0.5 mg/l of phosphate. Newly constructed ponds require higher initial fertilization rates. Organic fertilizers have to be applied as often as possible and almost daily. In Israel, manure (as dry organic matter) is applied daily at 2-4% of the fish biomass. Few parameters have to be carefully monitored and fertilization should be immediately stopped if dissolved oxygen falls below 4.0 mg/l, pH above 9.0, or water transparency below 25 cm.

A number of country-specific fertilization guide for tilapia pond culture are summarized in Table 7.  The fertilization regime used will, among others, depend on the management system (extensive versus semi-intensive), stocking density (no./ha)/biomass of fish (kg/ha) and type of fertilizers used (organic, inorganic or combination).  Site specific factors other than nutrient input that affects primary productivity (e.g., weather) makes it difficult to provide a general pond fertilization guide for tilapia farming. Therefore, the information provided in Table 7 is intended purely as a general guideline.  In Thailand, chicken manure applied weekly at 200-250 kg dry weight/ha together with urea and triple super phosphate (TSP) at 28 kg N and 7 kg P/ha/week, respectively, produced a net harvest of 3.4-4.5 tonnes/ha in 150 days at a stocking density of 3 fish/m2 or an extrapolated net annual yield of 8-11 tonnes/ha.

In Honduras where there is sufficient dissolved phosphorus in the culture water, weekly application of chicken manure at 750 kg dry matter/ha and urea at 14.1 kg N/ha yielded 3.7 tonnes of tilapia/ha when stocked at 2 fish/m2. Grow-out tilapia ponds in Indonesia are fertilized with urea, TSP, and manure at 2.5 g/m2/week, 1.25 g/m2/week and 250 kg/month, respectively, together with a feeding regime of commercial tilapia feeds (Nur, 2007).

Summary of fertilization practices for Nile tilapia in three different countries:

One of the interesting ways to improve pond productivity is to practice polyculture with common carp or shrimp. While feeding, common carp stir up the substratum and this releases nutrients into the water column and therefore enhances primary production. In extensive farming systems in Africa and Asia, bamboo poles or tree branches are planted within the ponds to increase natural productivity. These substrates increase the surface area for enhanced periphyton production (Figure 9), which is grazed by the fish. More recently, synthetic substrates (Aquamats) for bacteria and algae have been used in tilapia and shrimp culture systems. Although tilapia is a hardy fish and can tolerate extremes in most water quality variables, they should not be exposed to low dissolved oxygen for longer period as it negatively affect the metabolism resulting in reduced growth (Stickney, 1996). Tilapia cannot tolerate water temperature below 12°C (Tom Hecht, Pers. comm.). Pond culture of Nile tilapia with shrimp, leads to improved feed utilization efficiency, reduced environmental pollution and improved production (Yi et al., 2003).