An incurable fungal disease is killing large numbers of fish in the Zambezi River Valley. The UN Food and Agriculture organization says food security and the livelihoods of people in seven African countries could be seriously affected.
The disease is called Epizootic Ulcerative Syndrome, or EUS for short. It causes ugly lesions on fish and is spreading both upstream and downstream in the Zambezi.
FAO Senior Fishery Resources Officer Rohana Subasinghe says EUS is fairly new to Africa, first seen there in 2007. But other regions of the world have felt its effects for a long time.
"This is an old story in a new form because this disease has been devastating Asia for a long time… killing all sorts of fish, many species, devastating people who are living on fish," he says.
The disease has also been found in Australia and the United States but over the years may have been called by a number of different names.
Decimating fish populations
Subasinghe says it appears the disease may first take hold in fish that are bruised or have skin damage.
"Then, this particular spore of this particular pathogen can go inside…to grow within the musculature and also can go into the internal organs," he says.
EUS, with its "ulcerative lesions" can "decimate" fish populations.
"We have experienced in Asia mass mortalities of fish
-- hundreds and thousands of them dying over a period of months," says Subasinghe.
As many as 20 varieties of fish may be susceptible, including tilapia, a staple food in the Zambezi basin. Tilapia is very popular in other parts of the world as well and is often grown in fish farms.
Tracking down the cause
FAO officials don't know for sure, but they think the disease may be triggered by environmental factors -- things like water temperature or the rainy season.
"In Africa, the rainy season begins around October, November. So we suspect to see another round of disease outbreak around October, November this year," he says.
As fish die off, the catch in subsequent years will be smaller. That increases food insecurity and raises the prospect of food aid.
"This has managed to almost completely eradicate certain species in the systems. I am a Sri Lankan. I have seen [it] in Sri Lanka. But it took four or five years to see these fish coming back in the rivers," he says.
EUS is very difficult to control in the wild, but it can be controlled in fish farms. The FAO says many fishers in the Zambezi River Valley may need to diversify into fish farming to maintain their livelihoods.