Haenen OLM † , Engelsma MY †, Roozenburg I †, Kerkhoff
S†
† National Reference Laboratory for Fish and Shellfish Diseases, Central
Institute for Animal Disease Control (CIDC-Lelystad), Wageningen University
and Research, Lelystad, The Netherlands
Literature on fish diseases deals mostly with problems in intensive aquaculture. However, in wildlife many more fish species are present, in lower densities. This probably results in a lower number of disease outbreaks with a lower severity, but higher variety, many of which go undetected. Nevertheless, when water quality is sub-optimal, or when wild fish populations meet cultured fish, disease outbreaks in wild fish may be very serious. As international transports of live cultured and ornamental fish increase, more and more diseases are spread worldwide. In case of mortalities of wild fish, mostly only toxicological investigations are done. It is important to look for infectious causes as well, including infections with Koi Herpes Virus, Edwardsiella tarda , and Herpesvirus anguillae.
Koi Herpes Virus (KHV) is spreading rapidly over the globe. The virus is only pathogenic to koi and common carp ( Cyprinus carpio ). Since last year KHV has invaded Japanese wild carp, causing high mortalities, after transmission via cage cultured consumption carp. These cultured carp were probably infected through restocking of infected koi, which had contact with imported KHV positive koi. The KHV has caused mortalities in expensive koi in Western Europe since 1997, but not yet in carp. In the UK wild carps are found positive for antibodies against KHV as well. The angling community is worried now about impact of KHV to wild carp populations. Since KHV has been detected in wild carp, some authorities involved in fish management are taking the problem seriously and are organizing and paying for veterinary investigations of wild fish.
dwardsiella tarda is a bacterium causing acute sepsis in mostly cultured eel, and Herpesvirus anguillae (HVA), originally from East-Asia, causes mortalities in eels, when they are under stress. Last year there were high eel mortalities in our country in the river Nieuwe Merwede during a very dry and hot summer month. The water had decreased to a minimum, and it had an extreme high Biological Oxygen Demand. A double infection of E. tarda and HVA was diagnosed in the stressed eels.
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