A Walter Sisulu University (WSU) study has found that adding green Rooibos extract to tilapia feed improves fish growth rates and feed efficiency — a breakthrough with potential to support more sustainable aquaculture in South Africa.
Prof Grace Okuthe, Senior Researcher, Walter Sisulu University.
The trial, led by Prof Grace Okuthe of WSU, compared commercial feed with feed enhanced by fermented (red) and unfermented (green) Rooibos extract. Tilapia fed green Rooibos grew 2.83% faster and converted feed into body mass 0.9% more efficiently than the control group.
"These may sound like small numbers," says Prof Okuthe, "but in commercial aquaculture, even fractional improvements in feed conversion translate into substantial cost savings, faster production cycles and reduced environmental impact."
Why Rooibos works
Researchers believe Rooibos’ bioactive phenolic compounds make feed more palatable, support gut health and improve nutrient absorption. The study also suggested DNA protection benefits in the fish.
"These compounds work in harmony with the fish’s digestive system, helping them get more from the same amount of feed," Prof Okuthe explained. "It’s not about adding protein or calories – it’s about enhancing the efficiency and resilience of the fish."
Environmental and economic potential
Better feed efficiency means less waste entering water systems — reducing nutrient runoff and algal blooms. Rooibos, cultivated only in South Africa’s Western Cape, could also open new income streams for growers if commercial aquaculture demand develops.
"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," says Prof Okuthe.
Scaling up the innovation
For large-scale adoption, challenges include maintaining extract potency in feed manufacturing, ensuring a reliable supply, and testing across different environments. Regulatory approvals and long-term studies on fish quality and taste will also be required.
The team plans to extend research to other aquaculture species such as freshwater fish and shrimp.
Global context
Aquaculture now produces more than half the world’s fish for human consumption, and tilapia is one of the most widely farmed species. Natural, locally sourced additives like Rooibos could help producers meet protein demand without adding pressure on marine ecosystems.
"South Africa has an opportunity to lead here. We’re combining heritage, science and sustainability in a way that resonates with global markets," emphasises Prof Okuthe.
