Carp Edema Virus or CEV is the scientific name for the disease that is more commonly known as sleeping sickness or sleeping disease. CEV or sleeping sickness are a response to extreme stress, often caused by parasite and viral infections in fish populations. Possible signs of fish with CEV infected will demonstrate behavioral abnormalities including unresponsiveness and lethargy, lying motionless on their sides or bellies on the bottom of the tank for long periods of time unless disturbed.
In sleeping sickness, weakened juveniles may swim slowly and aimlessly along the edge of the pond/ aquarium or hang motionless just under the surface of the water. Further supporting evidence of CEV may be obtained by examining wet mounts of the gills. In the early stages of the disease, the gill epithelial cells at the tips of the gill filament proliferate, resulting in a thickening or “clubbing” appearance. In CEV-infected fish, the proliferation may extend to the base of the gill filament and impair gill function.
In addition to an appropriate case history and clinical signs, further supporting evidence of CEV may be obtained by examining wet mounts of the gills. In the early stages of the disease, the gill epithelial cells at the tips of the gill filament proliferate, resulting in a thickening or “clubbing” appearance. In CEV-infected fish, the proliferation may extend to the base of the gill filament and impair gill function.
Water temperature is an important factor in the occurrence of CEV, although this depends on their living conditions as environmental factors considerably influence disease. CEV typically occurs in the rainy season among juvenile koi after they have endured the stress of being moved from green-water earthen nursery ponds into clear-water concrete-lined ponds for grading. Presumably juvenile koi are exposed before or during the stress of capture and subsequently show signs of the disease. As mentioned above, fish may also lie on the bottom of the tank in situations where CEV is absent. This phenomenon typically occurs after harvest from ponds when water temperatures exceed 27°C (80°F).
Cure and Prevention
When the signs in Koi suggest CEV infected, a simple salt bath is a common treatment for koi sleeping sickness. Salt baths are especially useful when no other diseases or infections are present. Add dried salt at 0.3% or ½ an ounce per gallon (3 grams per litre) of water in a quarantine tank, and increase the temperature to 32°C (89.6°F). The salt level can be increased after 12 hours to 1oz per gallon or 0.6% (6 grams per litre). If the disease affecting only a few of the population, quarantine all the sick fish to prevent further contagion and keep the affected fish in the solution at least for 2-4 days.
The best way to prevent CEV is with implement an effective quarantine procedure, all new fish must be kept in a separate system, ideally in a different building or area from the resident fish. Quarantine (separation new fish) is the most dependable method to avoid the introduction of pathogens into a pond or facility. Adding 0.5% (5g/L) salt of water in a new fish quarantine tank helps to prevent the disease after suffer the stress of moving.
Prevention and control depopulation also highly recommended. Koi owners should understand the potential for ongoing disease and spread and monitor for signs of trouble. Best health management practices should be followed to minimize the risk of CEV outbreaks. To keep fish healthy and better able to resist disease, quarantine and test new fish; avoid crowding and stressful events; maintain good water quality; and provide proper nutrition.