In the backyard of a Swahili house in Kisauni, Mombasa County, Omar Dhadho grows horticultural crops and keeps catfish in a concrete tank.
Dhadho started this in a bid to better use the space behind his house. The landlord gave him the nod to construct the tank and undertake the type of farming that is known as aquaponics.
Aquaponics is practised in urban areas.
It combines aquaculture (fish farming) and hydroponics (soilless plant culture). This enables one to save space and engage in two kinds of farming at once.
The tank allows water to circulate through the fish ponds, filters and plant beds. Then it flows back into the pond.
The nutrient-rich water that comes from the pond provides a natural source of fertiliser for the growing plants, which helps to purify the water in which the fish lives.
“Water that has fish feed waste is pumped from the tank into the bucket. The unclean water has mineral content that includes ammonium and nitrates that are absorbed through filtration by the plant roots to make it clean.
Then the water flows through pipes by gravity, back into the tank and is re-circulated. There is (a) symbiotic relationship between the fish in the tank and the plants in the bucket.”
“I started the project last November after buying 400 fingerlings from a farmer in Nairobi at Sh8,000, but during transportation, 150 died due to improper handling. I made a loss of Sh3,000,” he said.
The remaining 250 fingerlings became his first stock.
Starting out was not easy. The fish tank was not well constructed and it leaked. This again led to losses as some of the fish escaped.
“I brought a specialist to reconstruct the tank to minimise the loss of water and the fish,” says Dhadho, who is currently growing different vegetables and passion fruits.
Since he does not have a stable supply of water, he relies on a vendor to fill the tank. The supply of 3,200 litres costs him Sh400 every two weeks.
“I look forward to owning my own plot to dig a borehole and build more tanks to be able to sustain myself and reduce costs,” he says.
Catfish takes about six weeks to mature. Each kilo of catfish goes for Sh500 in Mombasa.
“I am in the process of reworking the aquaponic system so that I can grow vegetable all year round for domestic and commercial consumption,” he explains while showing the 21 buckets that form part of the system.
“The plants purify water that is circulated back into the tank. The products are organic,” says Dhadho, who graduated from the Technical University of Mombasa with a diploma in personnel management.
Harrison Karisa, the assistant director of aquaculture research at the National Aquaculture Research Development and Training Centre of the Kenya Marine and Fisheries Research Institute, says fish diseases are common in aquaponics due to the conditions of culture.
“The most common diseases are bacterial, fungal and parasitic infections,” Dr Karisa says.
Dr Karisa recommends that new fish should be quarantined before being allowed into the system to prevent the passing on of diseases.
“The skin of tilapia and catfish can be used to make leather products such as belts, bags and shoes.”
Donatus Njoroge, a lecturer in the Department of Physical Sciences at Mount Kenya University, says aquaponics saves a lot of water and one can control diseases.
For plants, Njoroge says there is no need for weeding and the growth of the plants is significantly fast compared to the traditional way of cultivating crops.
“The system has high initial costs but is self-benefiting since the waste from fish is the fertiliser for the plants,” Njoroge states.