Koi Edema Disease (also known as Koi Sleep Disease / KSD) is a viral disease caused by Carp Edema Virus (CEV) infection. It mainly affects common carp and koi, and is characterized by high infectivity and high mortality. The detailed introduction to Koi Edema Disease is as follows:
I. Etiology and Pathogen
Koi Edema Disease is caused by infection with Carp Edema Virus (CEV), which is known to be a type of carp poxvirus. The virus is the primary pathogen, while bacteria (such as Aeromonas punctata) may act as secondary pathogens involved in the infection. Unfavorable environmental factors (such as deterioration of water quality and sudden changes in water temperature) can exacerbate the progression of the disease.
II. Symptoms and Classification
The symptoms of Koi Edema Disease can be divided into acute and chronic types based on the course of the disease:
Acute Type:
In the early stage of the disease, the skin and internal organs of the affected fish show obvious hemorrhagic inflammation, and the skin becomes red and swollen.
Due to congestion and inflammation, the sides and abdomen of the body develop edematous erythema of different shapes and sizes.
The base of the fins becomes inflamed, and the tissue between the fin rays is damaged, forming "eroded fins".
The anus is red, swollen, and protrudes outward; the scales all over the body stand upright; the gills appear pale; and the entire body is edematous.
As the disease progresses, the affected fish move sluggishly, swim alone away from the school, exhibit lateral swimming, sometimes lie still at the bottom of the water, have difficulty breathing, and stop eating and moving.
Finally, the caudal fin becomes rigid, losing the ability to swim, and the fish dies soon after. Fish with the acute type of the disease usually die within 2 to 14 days.
Chronic Type:
At the beginning, the superficial layer of the skin shows local inflammatory bleeding, with epidermal erosion and scale loss.
Subsequently, ulcers form, muscle necrosis occurs, and the adjacent tissues become inflamed and appear red and swollen.
Sometimes, local scales stand upright, and the fins are congested.
The chronic type has a long course of onset, which can last for 45 to 60 days or even longer. Some fish may recover naturally, but others may die from the disease.
Before death, the fish is often accompanied by general edema, ascites (fluid accumulation in the abdominal cavity), and exophthalmos (protruding eyes).
III. Epidemic Situation
Koi Edema Disease occurs in most areas of China, mainly endangering 2 to 3 - year - old common carp. The disease is most prevalent during the spawning and hatching season of common carp. The mortality rate of common carp in infected fish ponds can reach 45%, with a maximum of 85%, and the mortality rate of common carp in adult fish rearing ponds can also exceed 50%. In addition, the disease has appeared in China, causing high mortality rates of common carp and koi in some aquaculture farms.
IV. Diagnostic Methods
Preliminary Diagnosis: A preliminary diagnosis is made based on the clinical symptoms of the affected fish (such as enophthalmos, gill rot, and skin damage) and the epidemic situation (such as the onset of the disease when the water temperature is low).
Confirmatory Diagnosis: Confirmation is achieved by observing poxvirus - like particles in the sections of the internal organs of the affected fish and detecting the gene fragments of CEV using PCR and Real - time PCR methods.
V. Prevention and Treatment Methods
Prevention Measures:
Strictly prevent fish from being injured: Injured fish should not be used as broodstock, and it is even more important not to keep injured fish together with healthy fish.
Disinfect spawning ponds: Remove sludge from spawning ponds and disinfect them with bleaching powder or quicklime.
Optimize hatching conditions: Maintain a stable water temperature during hatching (e.g., around 28°C) and avoid sudden changes in water temperature.
Control inbreeding: Avoid inbreeding and introduce high - quality breeding stock.
Adjust feed: Use nutritionally balanced feed and supplement necessary vitamins and minerals.
Regular disinfection: Regularly disinfect the water body with drugs such as copper sulfate to prevent parasite infections.
Treatment Methods:
So far, there are no effective treatment methods for Koi Edema Disease, and prevention is the main focus.
For fish that have already developed the disease, auxiliary treatment can be attempted by injecting drugs such as oxytetracycline, but the effect is limited.