Sustainable Use Of Existing Irrigation Water Bodies By Means Of Aquaculture In South Africa: A Case Study

There are numerous water bodies in South Africa that have the potential to be utilised for aquaculture practices without an additional load being placed on water consumption. For example, the Western Cape has over 2 000 irrigation dams each with a water volume in excess of 500 000 m3 which are suitable for aquacultural activities and have the potential to produce an estimated 5 800t of freshwater fish per annum. The question that arises is whether the fish enrich or pollute the water relative to the primary function of that water, e.g. irrigation of high value crops such as table grapes and deciduous fruits destined for export. One of the major chemical compounds derived from an aquaculture industry causes an increase in the nitrogen content of the water, which is caused by both excess feed decomposition and fish metabolism. An intensive investigation of an integrated agricultureaquaculture project in the Western Cape showed no negative impact of the aquaculture activity on the water quality in terms of nitrogen, pH, turbidity, conductivity or total dissolved and suspended solids content. The aquaculture project delivered 4 500 kg of trout over a seven month growth period in a cage system which realised a return of 17.2% on the investment.