Deadly infection hits Zambezi fish

Experts are baffled by the never-before-seen malady, which observers fear could spell doom for the region’s lucrative fish industry.

The Zambezi flows through eight southern African countries – Angola, Botswana, Malawi, Mozambique, Namibia, Tanzania, Zambia and Zimbabwe – before disgorging into the Indian Ocean.

The infestation manifests in blisters and serious sores that have led to death among some fish species, notably the widely sought after breams, minnows and catfish.

Expert opinion is divided as to the nature, cause and extent of the infestation, with one school of thought holding that a parasite could be behind the menace, while another points to bacteria.

While parasitic infections among fresh water fish in southern Africa are not an entirely new phenomenon, it is the sudden increase of the infestations that has caused panic among water biologists, an expert concluded.

There are fears that some fish mongers and some villagers in Namibia’s Caprivi strip could be eating some of the infected fish without knowing or feeding them to dogs and selling other less infected ones to unsuspecting consumers.

This has added to the panic and heightened fears that the infestation can be passed onto humans.

Some birds that include herons were on one occasion were observed feasting on dead minnows across the Mwandi Khuta on the Namibian side.

This was observed on the 27th of October.

The Southern Times has it on good authority that some samples of the infected fish and water have been sent to South Africa from Namibia.

Zambian authorities have also collected samples which are being examined at the University of Zambia’s Samora Machel School of Veterinary Medicine as experts frantically try to comprehend the cause, extent and likely consequences of the outbreak especially to the fish industry along the Zambezi.

There is a serious dearth of parasitologists in the region and the lack of a holistic and concerted effort by experts in the affected countries has added to the exasperation.

Zimbabwe has only one scientist who is trying to be a parasitologist and Professor Christopher Magadza – a world-renowned Zimbabwean limnologist says one can count on one hand the number of expert fish biologists in the region.

Commenting after being shown photographs of some infected fish species by The Southern Times last week, Magadza, a water expert for over 30 years, said the infestation was “very serious” and hazarded that parasites were involved.

“It could be a sudden arrival of migrant birds; they rest in the Sud in Sudan on their way to Southern Africa. Higher temperatures promote the rate of development of the secaria and some fish parasites can be transmitted to humans,” he said.

The upper Zambezi basin plays host to many migratory bird species.

There are fears that the parasite, suspected to be a nematode brought into Southern Africa by migratory birds, could now be spreading into the mighty Zambezi River, Lake Kariba and Cahora Bassa, which support some of the region’s biggest inland fisheries.

Informal reports from local fishermen along the Zambezi Fisheries indicate severe fish deformities and a worm-like parasite causing large sores on breams, catfish and other freshwater species.

The parasite was observed in different fish species, mostly those forming the backbone of the subsistence and semi-commercial fishing industry, triggering fears that humans could be exposed to the malady.

“Fish parasites usually do not affect humans, but some can cause muscular cysts and intestinal worms,” said Magadza, who has just retired from the University of Zimbabwe.

He added: “The parasites look like nematodes usually carried by migratory birds.

“Extremely high temperatures can also cause the rapid multiplication of fish parasites, and this seems to be a very serious infestation, but the lack of data on water temperature and fish deformities makes it difficult to read the trends,” Magadza, who was once the scientific director of the University of Zimbabwe’s Lake Kariba Research Station for over 10 years, said.

Magadza said herons and cormorants are the most likely agents spreading the fish parasites, and said nothing much could be done to control the parasites since they occur in natural ecosystems.

Namibia, Zambia, Botswana, Zimbabwe and Mozambique lie in the wake of the fish deadly infection, but have no fish pathologists. The suspected parasite has been observed to be eating away at the fins and tails of breams, catfish and other fish species.

“There are at least 15 known fish parasites at Lake Kariba, and they occur naturally,” said Magadza.

“What is interesting is to know what has caused the sudden increase in infection.”

He said the rate of mortality would determine whether fisheries in the region would be impacted by the parasites, though informal reports indicated that up to eight in every 10 fish were infected.

“Fish must be cooked thoroughly; otherwise people might ingest fish parasites from smoke dried fish since drying does not kill the fish parasites.”

Magadza ruled out chances that the fish could have been poisoned since worm-like parasites were reportedly removed from some of the dead fish and said they would not have sores if it were a result of poisoning.

“In serious infestations fish will rub areas on their skin or fins raw and develop skin and fin infections. Sometimes they will just act funny, or suspend at an odd angle in the water. They might even jump out of the water,” said Ray Jordan, a fish pathologist on his website.

“Sometimes the opposite is true. Fish will lie on the bottom with fins tightly clamped to their bodies. They can either be extra slimy showing a whitish film or almost lacking a slime coat. They can have irritated reddish spots or streaks on their backs, sides, or bellies.”

Mr Charles Maguswi, Zambia’s director of fisheries concurred that the infestation was without precedent and very serious.

“We have collected samples and taken them to the Samora Machel School of Veterinary Medicines in Lusaka after interviewing locals in the affected areas. This is something we have never seen before and we have been discouraging people from eating the affected fish. While conclusive findings are still pending, preliminary tests suggest that it is a bacterial infection,” Maguswi said.

He added: “We acknowledge that something is very wrong and we are determined to establish what it is. We cannot rule out the possibility of the infection affecting humans. Already there are unconfirmed reports that some people who ate some affected fish fell sick and our officials are on the ground talking to medical officials who may have treated these people. This is serious. I have never seen anything of this sort in the 19 years that I have been working in fishery.”

Maguswi said Zambia and Namibia where very active in responding to the outbreak. He said because of the transfrontier nature of the nuisance, it was critical for experts in all affected countries to share notes over the issue.

Shaft Nengu, Botswana’s deputy director of fisheries concurred.

“I think this is a regional problem and we are thinking of a collaborative effort in dealing with it. My view is that it should not be left to individual countries to deal with this problem and we must not leave it to the fisheries departments. We need a holistic approach and everyone must be involved, including health officials and veterinary officials,” he told The Southern Times on Wednesday.

He would neither confirm nor dismiss reports that some fishermen had detected the same problem among fish in the Chobe River.

“As I said we have not really done much as this is something that has just been brought to our attention,” he said.

However, fishers in Ngoma on the border between Botswana and Namibia have reported seeing infected fish in the Chobe.

People in Botswana are not allowed to fish in the Chobe because it is a national park.

Dr Nyambe Nyambe, a Zambian social scientist-turned consultant with a keen interest in environmental and developmental issues, has been following the outbreak closely.

He said although it is difficult to determine the source of the infestation, some fishermen in Katima Mulilo in Namibia began reporting serious sores on some fish in the area in early October.

“The problem was reported in Ngoma and areas around Nakabolelwa on the backwaters of the Zambezi. When in flood, water bodies in these areas get connected to the Zambezi River. Towards the end of October similar problems were reported in Mwandi area in Zambia. The affected fish – mostly minnows and breams – had very frightening wounds on different parts of the body,” he said.

He also bemoaned a lack of a coordinated response to the outbreak and said there was need to get to the bottom of the matter given the size and importance of the Zambezi River.

Efforts to contact Dr Clinton Hay, Namibia’s chief fisheries biologist, were in vain. Namibia’s Permanent Secretary in the Ministry of Fisheries and Marines Resources, Nangula Mbako, was said to be in a meeting while the Minister, Dr Abraham Iyambo, was said to be out of town.

There is very little literature on fish pathology in Southern Africa, with most literature having been compiled by French fish pathologists in West Africa. The training of fishermen in the region has not extended to quality control, and they still concentrate on business, weight and numbers.

“It’s an area that interests taxonomists (taxonomy is the branch of science concerned with clasification), because there’s very little that can be done to control fish parasites. If the parasites are found downstream from a community then it would be attributed to effluent but in this case it seems unlikely,” Magadza said.


Fish parasites are ubiquitous in freshwater, marine, and terrestrial environments, where they often outnumber other animals in both individual and species counts, and are found in locations as diverse as Antarctica and oceanic trenches.

(Additional reporting by Tawanda Kanhema in Harare)


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