The main challenge in aquaponics – the combination of raising fish (aquaculture) and growing plants without soil (hydroponics) – is the imbalance between the nutrients of the fish and the plants grown in the system, as each has its own nutritional requirements.
“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," says Dr Oyama Guwa, who obtained her doctorate in Chemical Engineering on Tuesday (15 December 2020) at SU's December graduation.
As part of her study, Guwa conducted experiments to design fish feed that would provide optimal nutrition to the African catfish, and help plants grow at the same time. Asked about the reason for using the African catfish, she points out that the species is often used for research because it is easy to grow and tolerates poor water quality.
Guwa says the practice to date 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.
“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 points out 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.
Highlighting the significance of her research, Guwa says “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 adds that “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."
“My study showed 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.
Also, it reduces the labour of constantly adding minerals to the aquaponics production system, as the nutrients are already contained in the fish feed."
Guwa says this novel fish feed helps increase the performance and efficiency of the aquaponics system as well as the breeding of the African catfish.
She mentions 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."
- Photo: Dr Oyama Guwa at the graduation. Photographer: Stefan Els
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