- By Andrea Dijkstra
- Economic journalist, Kenya
“It was horrible,” Allan Ochieng says of the disaster that struck Lake Victoria fish farmers late last year.
Thousands of fish were killed when Africa’s largest lake experienced a recurring natural phenomenon called upwelling.
This happens when deep water mixes with surface water, causing a sudden depletion of dissolved oxygen in the water, killing fish.
Some farmers believe high levels of algae or pollution may have played a role.
Mr Ochieng lost all of his 120,000 tilapia, half of which were almost ready to be harvested. Many other farmers suffered similar losses.
With three partners, the entrepreneur owns 24 cages, near Ogal Beach on the Kenyan coast, which cost them around $100,000 (£80,000). They spent an additional $185,000 on the baby tilapia, food and labor.
“Cage fish farming carries huge risks but can also be extremely profitable,” says Mr Ochieng, determined to continue.
As the name suggests, cage aquaculture involves raising fish in a net cage. It has become one of the fastest growing food sectors in sub-Saharan Africa, as wild fish stocks have declined and demand for fish has increased.
Yalelo Zambia is the largest tilapia producer in sub-Saharan Africa, producing 25,000 tonnes of the fish at its facilities in Zambia’s Lake Kariba and the Ugandan side of Lake Victoria.
The company’s managing director, Ulric Daniel, says it is an increasingly high-tech sector.
“As we are dealing with a product that we cannot see, once it is underwater, we have to rely heavily on technology to measure what is actually happening below the surface,” said the director general at the BBC. He adds that cage fish farming is much more data-rich than, for example, the poultry industry.
He says all this data can help mitigate agricultural disasters like last year.
“Upwelling can occur quite suddenly, but certain indicators can predict its occurrence. This is why we measure dissolved oxygen, pH and ammonia content in the water daily,” explains Mr Daniel.
“As soon as we see the first signs of upwelling, we can reduce the number of fish in a cage to avoid mortality.”
Victory Farms, which is the largest caged fish producer in Kenya, also collects a lot of data.
“We measure multiple depths and locations to assess underwater activity and biology, assess algae in the lake as an indicator of upwelling and, in cases of reduced dissolved oxygen levels, check water currents. water as well as the level of algae accumulation on the lake. the nets of the cages”, explains general manager Joseph Rehmann.
“With seven years of historical data, we can now generally predict whether there is a high, medium or low risk of upwelling. If there is a high risk, we change stocking densities, reduce feeding and slow or let’s stop handling fish, both to reduce stress.”
Victory Farms has also developed technology to reduce losses when transporting live eggs to the hatchery.
She developed a mobile incubation system, which keeps eggs moving in oxygenated water.
The technology came from a project to build broodstock ponds on plots in the neighboring community.
In exchange, participants are paid for harvested fish eggs, which are then transported to Victory Farms ponds.
Such innovations are beyond the reach of the growing number of smallholder farmers who have ventured into cage fish farming.
“Although measuring oxygen levels in cages is extremely important, most smallholders do not do it because they cannot afford the required equipment, which costs more than $1,000,” says Dave Okech, President of Cage Fish Farmers Association Kenya.
Another problem, according to Mr Okech, is the lack of knowledge among most new farmers. “As a result, some set up their cages in water that is too shallow, which can cause water pollution and lead to higher mortality in the event of upwelling.
“Some entrepreneurs also use poor quality feed that sinks, which negatively affects the ecosystem and leads to losses as tilapia feed on floating pellets,” Mr Okech adds.
He believes more precise feeding would result in healthier fish and save farmers money.
His company, AquaRech, is currently working on a system that will monitor water temperature in cages.
He says this is key data because colder temperatures make it harder for tilapia to digest what they have eaten.
Armed with this information, its system can advise farmers on the exact amount of feed to use.
“We need this type of innovation to professionalize the sector and make it more productive and more beneficial for the people involved,” adds the Kenyan entrepreneur.
However, some are concerned about the rapid growth of this sector. There is concern about the considerable amount of uneaten food and fish excrement accumulating under cages and its impact on water quality.
“The presence of these environmental issues highlights the importance of responsible placement of fish cages, in sufficiently deep waters with sufficient water circulation,” says Chrisphine Nyamweya, a research scientist at the Institute of Marine and Fisheries Research. from Kenya.
Joe Rehmann of Victory Farms says his company and government officials test the water regularly.
“So far we haven’t had any problems with the carrying capacity of the fish,” he says.
He points out that overfishing has depleted Lake Victoria’s wild fish population.
“If Victory Farms has 3,000 tons of biomass today, we are adding to the nutrient load, but that is still well within the natural carrying capacity that existed before human overfishing depleted the lake.”