A study from Walter Sisulu University has discovered that adding green rooibos extract to tilapia feed significantly improves fish growth rates and feed efficiency. This finding could transform sustainable aquaculture in South Africa and beyond.
The study, led by Professor Grace Okuthe, a senior researcher at Walter Sisulu University in the Eastern Cape, compared commercial fish feed against feed enhanced with either fermented rooibos, the familiar red variety, or unfermented green rooibos extract.
In a statement, the South African Rooibos Council said the results were clear: tilapia fed green rooibos grew about 2.83% faster and converted feed into body mass 0.9% more efficiently than the control group.
“These may sound like small numbers, but in commercial aquaculture, even fractional improvements in feed conversion translate into substantial cost savings, faster production cycles and reduced environmental impact,” Okuthe said.
How rooibos works in fish feed
Okuthe said the team believes the effect is linked to rooibos’ bioactive phenolic compounds, which may make feed more palatable, promote gut health and improve nutrient absorption. The study also found evidence of DNA protection in the fish, suggesting an overall health benefit.
“These compounds work in harmony with the fish’s digestive system, helping them get more from the same amount of feed. It’s not about adding protein or calories, it’s about enhancing the efficiency and resilience of the fish,” she said.
The study highlighted that improved feed efficiency means less waste entering the water, which is a major environmental challenge in fish farming. Reducing nutrient runoff helps prevent algal blooms and protects aquatic ecosystems.
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The innovation also has clear economic potential for rural South Africa. Rooibos is cultivated exclusively in the Western Cape. A commercial-scale demand for green rooibos extract could create a new market for growers and support job creation in harvesting, processing and distribution.
“This research shows how an indigenous crop can open new economic pathways. In addition to the potential economic benefit to the industry, it also supports South Africa’s commitment under the Nagoya Protocol, ensuring that benefits flow back to the Khoikhoi and San communities, who are the traditional custodians of rooibos,” Okuthe noted.
She said rooibos has been part of South African life for generations, but now it’s finding a role in boosting sustainable aquaculture and addressing global food security.
“This research underscores how local biodiversity, paired with scientific innovation, can create solutions that protect the planet, while bolstering the country’s reputation in bio-prospecting.”
Opportunities and challenges
Okuthe said while the lab results were promising, commercial application would require careful scaling.
“We know the science works, but moving to large-scale production means ensuring a stable rooibos supply, maintaining the extract’s potency during industrial feed manufacturing and proving its benefits across different farming environments,” she said.
The next phase of research will explore testing the extract on other aquaculture species, from freshwater fish to shrimp, potentially creating a universal, natural feed additive.
Tilapia, in particular, is one of the most farmed fish globally, prized for its mild flavour, adaptability and affordability. A natural, locally sourced additive like green rooibos could help producers meet growing protein demand without increasing pressure on marine ecosystems or agricultural resources.
“South Africa has an opportunity to lead here. We’re combining heritage, science and sustainability in a way that resonates with global markets,” Okuthe emphasised.
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