Nutrient Pollution — Seafish


Oreochromis / Sarotherodon / Tilapia spp.

Nutrient Pollution

Tilapia farmers continually seek to improve the efficiency of feeding methods in order to reduce operational costs and to minimise the waste of feed. Waste feed, along with other organic discharges from farming operations, can potentially lead to pollution of receiving waters and adversely affect aquatic life through de-oxygenation and algal blooms, which can be associated with nutrient increase. The key nutrients likely to cause problems for receiving waters are nitrogen and phosphorus1.

In land-based tilapia farming sedimentation basins, and grow-out ponds themselves, are effective in capturing the solid waste which arises from the farming process. However, once removed, the accumulated solid waste (or sludge) can be a significant source of pollution if not contained or disposed of properly. The use of pond sludge and/or waste water to fertilize agricultural land surrounding the farms is practiced in some production areas and holds potential for further development2. There are also some concerns over untreated dissolved nutrients, particularly at the end of the production cycle when ponds are drained, and large quantities of effluents leave the farming site1. However, the water from drained ponds could potentially be redistributed to other farming sites2.

One area of growing global interest is the use of clean-up technologies such as constructed wetlands which include harvestable aquatic plants that can help trap fine suspended particles and utilise dissolved nutrients3. These plants can then be harvested and used in various ways including fish feed production4, giving a farmer an additional crop and alternative income stream. Other solid farm wastes, such as dead fish and human wastes, can also pollute and impact the surrounding environment. In intensive tilapia pond culture, however, the use of inputs other than commercial feeds is likely minimal5. Farms should document and record how they dispose of sludge and any solid wastes such as fish mortalities.

As an open system, net-pen tilapia farming can result in direct nutrient pollution of the surrounding waters. For that reason, it is important that farms operate within the carrying capacity of the water body in which they are situated. To further improve their performance and limit the potential for environmental impact, farms should monitor the phosphorus and nitrogen concentration in feed, feed utilisation efficiency, the quality of farm effluents and water quality in the receiving water body. Monitoring methods are documented within certification standards1.

Recirculation of water within an aquaculture facility is often cited as a sustainable means of reducing environmental impacts from waste water discharges, as well as reducing escapees and helping diseases control6. The investment costs are significant and tilapia farmers are unlikely to consider this technology in low- and medium-income countries (LMIC) unless they receive a significant price premium for their products. There are similar small-scale tilapia producers in western Europe that grow tilapia for the restaurant trade in RAS and aquaponic systems. However, this is very much a niche activity with very limited production volume7.


  1. ASC
  2. Lin, C.K., Yi, Y. 2003. Minimizing environmental impacts of freshwater aquaculture and reuse of pond effluents and mud. Aquaculture. 226:57–68
  3. Akinbile, C.O. & Yusoff, M.S. 2012. Assessing water hyacinth (Eichhornia crassopes) and lettuce (Pistia stratiotes) effectiveness in aquaculture wastewater treatment. International Journal of Phytoremediation, 14:3, pp201-211
  4. FAO
  5. MBA
  6. MBA
  7. HIE