Perspective in Aquaculture

Groundwater extracted from arid areas is often unsuitable for irrigation, but it would be ideal for aquaculture.

Aquaculture in the desert sounds like a non-starter due to the lack of available water. However, many places in Southern Africa have abundant groundwater that could be used for aquaculture and irrigation. The Kalahari-Karoo multilayered aquifer stretches from eastern Namibia to southern Botswana and into western South Africa. In many places, it is between 75m and 400m deep; in others, it is close to the surface. If tapped into, this water could be made available for both aquaculture and irrigating large projects in this dry region.

groundwater from mines

In mines that penetrate deep into this aquifer, high-volume pumping is used to prevent flooding. In Botswana, a permitting condition of breaching the aquifer is that the water must be used sustainably and to the benefit of the environment.

Passing such water through fish ponds, which are then fertilised to increase primary productivity and therefore natural food for the fish, makes perfect sense. After passing through the ponds, a percentage of the water could then be used for irrigation. Irrigation projects in desert areas benefit from the abundant sunshine and long growing period; the swathes of green around Upington are testimony to this.

Desert soils are usually highly mineralised, and hence fertile. In southern and central Israel, citrus, olives and other crops are cultivated in the driest regions (annual rainfall as low as 100mm) using groundwater. It is here that Israel’s many fish farms are to be found.

Groundwater is not always of a suitable quality for human consumption due to mineralisation. One of these minerals is sodium chloride (salt), which is suitable for tilapia culture even at concentrations of up to 20ppt (parts per thousand). Such water is too saline for agriculture, with the maximum recommended salt content for irrigation usually 2ppt to 3ppt.

the kalahari- karoo aquifer could be tapped for aquaculture

One of the advantages of desert groundwater is that it is isolated from surface contamination, and therefore fish diseases and parasites are usually absent. The water is effectively sterile.

Where groundwater is available in arid regions, aquaculture can take place in several forms; large ponds, for example, can be constructed where suitable land and soils are available.

Egypt takes the lead here, with production in the best farms as high as 25t/ha. If water quantity is more limited, recirculation within closed systems or cage culture in refilled excavations would certainly be worth trying. There are inevitably some provisos: such systems require considerable skill to operate, rely entirely on artificial feeding, and obviously contain certain risks.

Large operations, such as open-cast mines facing a water drainage problem, would do well to consider extensive aquaculture projects using lined or unlined ponds. Even in climatically suboptimal areas with cold winters, solutions are available. These include overwintering of large fingerlings to shorten the growth period, the use of fastgrowing strains, and installing tunnels over the ends of ponds to create thermal refuges.

After all, Egypt successfully produces 750 000t of tilapia annually despite its cold winter.

nicholas james BELOW: The sun-baked Richtersveld. Aquifers in the dry western regions of Southern Africa hold great potential for aquaculture as tilapia can withstand the high saline levels often found in desert groundwater. Egypt and Israel, both extremely dry countries, have exploited aquifers to build thriving aquaculture industries.

by nicholas james Nicholas James is an ichthyologist and hatchery owner. Email him at farmersweekly@caxton.co.za. Subject line: Aquaculture.