Mighty Zambezi threatened by fish disease

Although the province is said to be the poorest of all the nine in the country, it has abundant natural resources that have remained untapped for a long time now.

But unfortunately, in November last year, a mysterious fish disease broke out in Sesheke district in Mwandi area in the Zambezi River down stream to Kasaya and Machile stream.

From December to January this year, no fresh reports were recorded as the levels of the infection went down but reappeared in March. But the prevalence of the disease rose in May and it spread to other districts. In June the fish disease had spread into the Kwando River in Shang’ombo district, a river that flows into the Zambezi River.

According to provincial fisheries officer, Kagoli Muyangali, the disease was also reported in Senanga in Luilela Stream, and four lagoons in Kalabo district which include Washiye, Mangomba, Sililo and Mulyata. Mr Muyangali said 60 per cent of fish in the upper Zambezi had been infected with the serious disease, which is scientifically called Epizootic Ulcerative Syndrome. All fish species are affected despite the disease being commonly found on breams, tiger and barbell fish that are mainly sold on the market.

Dumped
A source, from the agriculture office, said that the disease could have been caused by dead wild animals in neighbouring Botswana that were being dumped in the Zambezi River. However, he was quick to note that samples were taken to Lusaka to ascertain the cause.

A street trader, Regina Nyambe, who has been trading in the fish business since 1980, said it was the first time she had seen such a disease and was worried that the fisheries department might close because of the disease. She had only spotted the disease on barbell fish, locally known as Ndombe, and other species that were related to tiger fish locally known as Milumesi but has not seen any clinical signs on breams.

Another trader, Thomas Muyunda said selling fish was his main source of income as he has managed to raise and support his five school children through the fish business. He expressed concern that if the fishery closed, he would suffer because there were no other potential businesses he could engage in.

But Mr Muyangali said there were no immediate plans to close the fisheries. His department was currently carrying out investigations to establish whether the fish disease had any effects on human life and the exact cause. He has urged people in the province to be careful when buying fish and look out for clinical signs such as blisters, bruises and sores on fish bodies.

According to correspondence obtained from the Institute of Aquaculture, University of Stirling Scotland Website, Epizootic Ulcerative Syndrome (EUS) has been affecting a wide range of fish species in the south and south-east Asia for the last two decades. EUS has been recognised as the single most potentially damaging disease of fish in that area.

What are the signs?
According to the Aquatic Animal Diseases in Australia, fish with the disease may have sores on the body, red spots, black burn-like marks or deeper ulcers with red centres and white rims. However, the disease may still be present in fish in the absence of any signs. The gross signs of the disease in an infected fish are fungal hyphae (threads) sometimes extending into visceral organs and liquefactive necrosis of the tissue.

The researchers say the disease has often been associated with acid water run-off and can appear after heavy rains particularly after a long dry period. Collecting samples should be done with care as some aquatic animal disease agents may pose a risk to humans therefore, people should not try to collect samples unless they have been trained. This is due to the uncertainty in differentiating diseases using only gross signs.

Disease agent
A fungus, Aphanomyctes Invadans, seems to be the primary cause of the disease but other agents like water quality factors may also play a part in the expression of the disease. Scientists have identified the mysterious disease that is killing fish in parts of the Zambezi River to be EUS caused by a fungal pathogen. The researchers say that this is the first known outbreak of the disease in Africa, but they still do not know how the pathogen got into the Zambezi River that flows into eight southern African countries.

Source: TimesOfZambia