Rainbow trout

Oncorhynchus mykiss


1. What is it?

Rainbow trout (Oncorhynchus mykiss) are freshwater species native to the Pacific Ocean in Asia and North America. They have been introduced into at least 45 countries for food or sport. In some areas trout have negatively affected the environment by outcompeting or eating native species, transmitting diseases and hybridization with closely related species. Trout were introduced in South Africa as an alien fish species about 100 years ago and have invaded many local river systems.

2. How was it caught or farmed?

Farmed - Tanks

Rainbow trout are farmed on land in special tanks known as RAS tanks (Recirculating Aquaculture Systems). This system is a recirculating system which means it is either fully or semi-closed to the ocean. Juveniles are hatchery based from locally produced sources. Rainbow trout rely on a low-moderate amount of feed, both protein and terrestrial based. The main risks include the escape of fish and the discharge of nutrient waste into the river system. However, there are management measures in place to regulate these impacts.

Imported - Freshwater cages

Rainbow trout are farmed in Lesotho using cage culture. Juveniles are hatchery imported from South Africa. Rainbow trout require a low-moderate amount of feed. Normally, cages have a high waste discharge however the farms are located in the Katse Dam which is a man-made with a significant flushing factor. While there is a risk of escapes as well as spread of disease, the impact on the wild population is limited.

3. Where is it from?

Farmed - Tanks

Trout is farmed mostly in the Western Cape and Mpumalanga with smaller producers in KwaZulu Natal. There are specific zones for trout farming so as not to further introduce the species into other local river systems. Management is considered to be partly effective as the treatment of water before discharge is often not regulated and ecosystem-management strategies in certain areas are not clearly defined.

Imported - Freshwater cages

Rainbow trout is farmed in the Katse Dam in Lesotho. There is a strict monitoring protocol in place by the Lesotho Government to ensure that there are no significant impacts on the surrounding ecosystem. Farms are audited twice a year with regards to environmental reporting and there is an efficient regulatory framework that addresses the majority of concerns.


Fishing Type: Aquaculture (freshwater cages)

Origin: Imported - Lesotho

Trout are farmed in cages usually anchored in dam and lakes. The fish need to be fed artificial food that includes wild-caught fish. An ecological impact of trout farming, in addition to the escape of alien species, is the discharge of nutrient waste into river systems. However, farms are required to filter their water before its released. Otters and cormorants can get entangled in the netting surrounding cages.

Fishing Type: Aquaculture (ponds)

Origin: 🇿🇦South Africa

Fish are farmed in semi-closed ponds, cages and fenced-off pieces of river, usually in areas previously used for other agriculture, but as the industry grows, land-use could become a concern. There are no control measures in place for feed, and although some nutrients are released into the environment, the effect is moderate.