Trout are the only cold-water species farmed in South Africa. This is unsurprising as South Africa has few places in which cold-water fish farming is viable. Despite these limitations, trout farming comprises the country’s most successful form of aquaculture. Trout originate in northern Europe and the USA, where they have been cultured commercially for more than a century.
Introduced as a sport fish into South Africa in 1890, trout were first bred at the Jonkershoek hatchery near Stellenbosch, and first farmed commercially at Maloney’s Eye fish farm. They are fine table fish, with firm, pinkish, flesh, a simple backbone, and scales that do not need to be removed prior to eating. They are easily domesticated, and can be fed on an artificial diet from an early stage. When insufficient, local stock is supplemented with imported trout.
Trout are spawned artificially. Gravid females are hand-stripped of eggs, which are mixed with the milt from ripe males, then spread on screens in cool running water until hatched, and the fry reared at high densities. Trout can be farmed wherever clean, cool and abundant water is available. Thus, the streams of the Mpumalanga escarpment, the Drakensberg and the Cape fold mountains are suitable.
The danger of warm water
Most trout farms use flow-through systems, whereby grow-out tanks are continuously refreshed with large quantities of new water, usually gravity-fed from nearby streams or rivers. Whether rectangular raceways or self-cleaning circular tanks are employed, the essentials remain the same – rapid removal of wastes and continuous replenishment of the system with highly oxygenated water.
The preferred water temperature for trout is 15°C. Below 10°C, growth is reduced, and at over 23°C, trout are severely stressed by low oxygen content. As most of South Africa has high summer temperatures, trout are at risk for several months. Early summer, before the rivers become swollen with rain, is a particularly difficult time for trout farms.
As an exotic fish, trout are regarded as an alien invasive species by conservation authorities, and blamed for predation and reducing biodiversity. With the new zoning regulations currently promulgated under the National Environmental Management: Biodiversity Act (NEMBA), intended to control the spread of invasive alien species, trout farming is now restricted even further in area. However, there is still good potential for cold-water fish farming where trout are already established in the catchment and sufficient water is available.
In contrast to the marine aquaculture industry, with its corporate-scale investments, trout culture is usually a family-run or small business in South Africa. As a result, many farms produce only 5t to 50t a year. However, marketing co-operation is high, and much inter-trading between role players takes place – a lesson well-worth following by the rest of the aquaculture industry!
Nicholas James is an ichthyologist and hatchery owner.