Protecting Valuable Koi Stocks
Koi Herpes Virus (KHV) is a distressing and deadly disease of common carp (Cyprinus carpio) and all its wild and ornamental varieties including mirror, leather, ghost and koi.
Within a carp stocked water, the disease is spread through fish to fish contact. However, poorly disinfected fishing tackle, fishery management equipment and even contaminated water, can transfer the virus between unconnected carp habitats.
Visual and Behavioural Changes
KHV infection shows itself as patches of white or brown dead tissue on the fish’s gills. Skin elsewhere on the fish might appear rough and flaking. A loss of protective mucus makes virus-infected carp feel dry when handled. Behavioural changes can include lethargy and hanging still in the water. KHV damage to a fish’s gills makes getting enough oxygen from the water stressful, so KHV affected fish may gather near aeration points such as inlets or fountains. Tissue damage leaves koi carp vulnerable to secondary invasion by parasitic fungi and bacteria.
As spring approaches, and water temperatures rise toward the virus’s activating temperature of 16-degree centigrade, carp fisheries and ornamental stocks – including mirror carp, leather carp, koi and ghost koi, risk large-scale mortalities of up to 100%.
Halting the movement of Infectious Stock
The Fish Health Inspectorate (FHI), Part A of the UK Government’s Centre for Environment, Fisheries and Aquaculture (Cefas) requires notification whenever KHV is suspected in carp stocked waters. In response, the FHI may temporarily suspend access to the affected water and halt the movement of potentially infectious stocks and equipment. After mortalities have ceased, FHI may prohibit restocking with carp species until after the following summer. This is to ensure that seasonally warming water doesn’t provoke a renewed outbreak. Even so, there is no guarantee that replacement stock won’t pick up an infection from surviving fish.
There is no treatment or cure for KHV, and because the virus may persist in fish surviving any outbreak of the virus, only careful biosecurity-management and constant monitoring offer any protection against potentially devastating infection.
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