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Carp Edema Virus
Behind this misleading name lies the Carp Edema Virus, or CEV, a virus that affects only carp and koi. The disease was first identified in Japan in the 1970s, before spreading to Europe starting in 2009. In France, the first cases were reported in 2013. Its common name comes from the behavior of infected fish: they become lethargic, lie motionless at the bottom of the water, and appear to be sleeping.
The symptoms are often characteristic. Infected carp swim very little, stop feeding, and barely react to stimuli. In advanced stages, they may lie on their sides, either at the surface or on the bottom, and have difficulty breathing. Physical signs also appear: excessive mucus, swelling, sunken eyes, and pale or damaged gills. In severe cases, death occurs due to anoxia, when the fish can no longer compensate for its state of exhaustion.
A spread influenced by various factors
Water temperature plays an important role in the onset of the disease. According to various sources, the virus can emerge in cool to temperate waters, with outbreaks frequently observed in the spring or during periods of significant temperature fluctuations. Stress, handling, the introduction of new fish, or the movement of contaminated equipment also contribute to the spread of the disease.
VHS is particularly feared for its contagiousness. It spreads from fish to fish, but also through water and improperly disinfected fishing or aquaculture equipment: landing nets, fish baskets, landing mats, or containers can all serve as vectors. Once established in a closed environment, it can spread very quickly and affect a large portion of the fish population.
A high mortality rate
The consequences can be devastating. In some cases, mortality rates reach extreme levels, sometimes killing nearly all the fish in a body of water within a few days or weeks. To date, there is neither a vaccine nor a truly effective treatment.
For fishermen, vigilance therefore remains essential. Cleaning and disinfecting equipment, avoiding the transfer of fish from one site to another, and reporting unusual behavior are all part of preventive measures. For behind this seemingly innocuous name, sleeping sickness is now one of the most serious threats to freshwater carp populations.
