The fish disease, Epizootic Ulceritic Syndrome or EUS for short, was recently diagnosed by researchers from the Aquaculture Research Division of the Department of Agriculture, Forestry and Fisheries, in barbel from a farm dam near Stellenbosch. The disease is caused by a fungus that is originally from Southeast Asia but has been spread to many other parts of the world by the movement of live fish and, possibly by the transport of contaminated water.
While confirmed diagnosis requires histological examination of the tissue and genetic screening for the presence of the fungus, alarming number of reports of fish with ulcers from all over Southern Africa has recently been recorded.
Disease to affect most fish species
Waters where suspect fish have been reported include Theewaterskloof Dam, Buffelsjagts and Arabie Dam in the Western Cape and more recently in Hartebeespoort and the Vaal Dam in Gauteng. Photographs of bass from Zimbabwe show species with similar ulcers and EUS has also been present in the Upper Zambezi and the Okavango Rivers for a couple of years.
Once introduced, the disease is fairly indiscriminate and has been reported to affect most fish species including popular angling species such as bass, barbel, carp, nembwe and tigerfish. Infection of fish requires the breaking of the skin for the fungus to get hold and once infected, the disease manifests itself in 3 stages. The disease progressed as follows: first, pinhead sized red spots form on the body and fins of the fish; these develop into small (2-4 cm) ulcers which finally form large open ulcers which eventually kill the fish. The distribution of the disease in South Africa is currently unknown. Unfortunately there is no research to show its long term impact on native fish stocks. But what researchers do know is that the disease spreads aggressively through fish populations once introduced.
Take action and control its spread
Unfortunately, there appears to be no feasible way to control this disease once it affects wild fish populations and the only control measure is to try to limit its spread in the country. It is therefore vital that all anglers understand that the only way to control this disease is to control its spread to new waters by doing the following:
- Do not move any fish, live bait or fish parts from one water body to another. Fish with no clinical signs may be carriers of the disease.
- Do not keep infected fish in your livewell is may result in the fungus being transmitted to healthy fish.
- Use knotless landing nets to minimize abrasions on the fish.
- Empty your live-well and bilges before leaving the launch site.
- Clean boats, trailers, fishing gear and drain live wells and bait buckets between fishing trips. If you have been outside South Africa, consider taking the extra precaution of soaking your live-well and bilge area with a solution of one 1 tablespoon of bleach (Jik or Jayes Fluid) to 5 liters of water for 10 minutes. Then rinse thoroughly to get rid of any remaining bleach (watch your carpets!).
- Help educate other anglers in the dangers of disease transmission.
By Olaf Weyl (South African Institute for Aquatic Biodiversity)
For more information send an e-mail to Olaf at firstname.lastname@example.org