Thabo Mohlala
December 15, 2020 would remain etched in Oyama Guwa’s memory for a long time. For it was on this very day that the Stellenbosch University virtually awarded her a doctorate degree in chemical engineering. This means from that moment on her name will be preceded by the honorific: doctor.
The focus of Dr. Guwa’s research area was on aquaponics, simply explained as the combination of raising fish (aquaculture) and growing plants without soil (hydroponics). She designed fish feed that is being hailed as innovative in that it provides “optimal nutrition to the African catfish, and help plants grow in integrated aquaponics system”.
Those who are familiar with this field of study say the main challenge with aquaponics is “the imbalance between the nutrients of the fish and the plants grown in the system, as each has its own nutritional requirements”.
But this can be corrected “by adding potassium and iron to the diet of the African catfish – eaten in countries in North Africa, Europe and Asia – aquaculture and aquaponics operators can optimise both fish nutrition and plant growth in their integrated aquaponics systems,” said Dr. Guwa.
When asked why she uses the African catfish as her area of focus, Dr. Guwa said this is because the species is easy to grow and tolerates poor water quality. She said currently the practice has been “for the nutritional requirements of fish to be met through fish feed, and those of plants through supplementary nutrients, which add extra costs to the production system”.
Said Dr. Guwa: “It’s therefore important to find ways to optimise nutrient levels in the waste excreted by fish so as to achieve maximum plant growth, without having to add any further supplements.”
She further explained that in normal aquaculture, fish excretions accumulate in the water and become toxic to plants. In an aquaponics system, however, bacteria break these waste products down into nutrients that plants can use, leaving the water circulated back to the aquaculture system cleaner and safer for fish.
Dr. Guwa said the significance of her research lies in the fact that the novel feed designed in this study has soya and fishmeal as its main ingredients and was developed specifically to meet the nutritional demands of catfish. “Given that plants too will benefit from this, the feed meets the needs of both aquaculture and aquaponics operators who now don’t have to buy additional nutrient fertilisers for their plants,” she said.
“The inclusion of potassium and iron in the diet of the African catfish improved its health, and the high concentrations of these minerals excreted in the water were absorbed by the plants and helped them grow,” she added.
“My study showed”, she said, “that adding the right amounts of potassium and iron to the diet of the African catfish can also improve plant growth, and reduce or even eliminate the need for additional nutrients for plants”.
According to Dr. Guwa, this also reduces the labour of constantly adding minerals to the aquaponics production system, as the nutrients are already contained in the fish feed. She said this latest fish feed helps increase the performance and efficiency of the aquaponics system as well as the breeding of the African catfish.
Dr. Guwa added that the South African aquaculture industry, which provides a means for secure and sustainable food production, is still growing and in need of support. “In South Africa’s coastal regions, the focus is mainly on marine species, while freshwater aquaculture still holds great potential because it can occur in all nine provinces. There is still room for further growth and research,” she said.
