The massive caged fish kills at Dunga Beach in Kisumu are due to reduced dissolved oxygen content in parts of Lake Victoria, a report shows.
The fish died of suffocation due to a lack of oxygen. This is according to a report by Kenya Marine and Fisheries Research Institute (KMFRI).
KMFRI released the findings after conducting a fact-finding multi–disciplinary study to ascertain the cause of mass death following distress calls by Dunga fish cage farmers.
The investigation was done under the supervision and guidance of the head of the Freshwater Directorate of KMFRI Christopher Aura.
Aura said the low oxygen concentrations was occasioned by urbanised pollution and climate change which resulted in algae blooming in the lake, especially in low oxygen concentrations producing a higher level of carbon dioxide, ammonia and hydrogen sulfide, hence four smell encountered during windy spells.
He said changes in weather variants between cool and hot conditions, has led to rapid decomposition of the algae affecting oxygen levels in the lake.
"Therefore, there exist increased algae concentrations at the cage site that are undergoing decomposition and utilising oxygen in the water causing low levels of dissolved oxygen which suffocates the fish," Aura said.
The director also noted that the existence of cages in shallow zones (<4.0 m) with little water space between the bottom of the cage and the lake bottom (0.6m against the recommended space of more than 2.0 m), and the clogged fish nettings, may have exacerbated the fish kills and deaths phenomenon due to minimal cases of water circulation and therefore very low oxygen levels.
"This is because, even though fish kills have occurred in the deeper waters, the shallow zones are more susceptible," he said.
Mitigation measures
According to Aura, fish farmers should be cautious about cage locations by consulting relevant authorities before setting up.
He said there is also a need for continued vigilance on lake use and possible pollution sources.
There is also a need for the establishment of an insurance scheme by insurance companies to cushion farmers in such cases.
According to the KMFRI survey, the first mortality was observed on April 10, 2023, when fish were seen coming to the surface of the water to gulp for air. This was followed by massive kills later the next morning.
A total of 60 stocked cages in the area with a density of 5,000 fingerlings each were affected.
The scientific study was undertaken on April 13, 2023.
This comes barely a day after the Kisumu county government distributed fish feeds and fingerlings worth Sh3 million to fish farmers in Ogal Beach.
According to one of the farmers George Opande, the death of the fish started on Wednesday but on Thursday, the situation became worse.
Opande said they have a total of 25 fish cages and had done harvesting in only five but unfortunately, they lost all the fish in the 20 cages.
He said each cage has 5,000 fish which are of different sizes sold within the range of Sh200-300 depending on the size.
"Yesterday when the fish death started, we removed the dead fish from some of the cages and dispossessed them but when we came back today, all the fish from the 20 cages were all dead including the fingerlings, which were only five months old," he said.
Opande noted that they have lost a lot and are even fearing to restock because they don't know what more could befall them.
David Okello, chairman of the Aquaculture Association of Kenya and also the Kisumu fish farmers cooperative society noted that the lake was very dirty and effluents were also being discharged which is affecting the fish farmers.
Okello noted that it takes a lot of money to put up such an investment and said the incident was unfortunate and a big loss to the fish farmers and efforts to revive fish farming in the area.
He asked the relevant agencies to enforce the relevant laws to protect the lake against pollution.
(Edited by Tabnacha O)