Viruses & biosecurity
CEV: carp oedema virus / koi sleepy disease
CEV is a different virus from KHV. It can damage the gills and cause serious illness in koi and other carp.
Why “sleepy” needs investigation
Marked lethargy, loss of appetite, swollen tissue and gill damage are reported. Poor oxygen uptake through damaged gills can leave fish distressed even when an air pump is running.
How it is distinguished
Symptoms and parasite scrapes cannot confirm CEV. A fish-health professional may arrange appropriate laboratory testing and investigate other causes at the same time. Do not treat repeated negative scrapes as proof that the fish are healthy.
Keep a useful case record
Record the first affected fish, new arrivals, temperature changes and treatments. Keep systems separate and contact a professional promptly if signs worsen or losses occur. Check the official reporting guidance for your location.
Sources & further reading
Original WakeyKoi wording, informed by the references below. Linked clinical resources explain the evidence and their scope; they have not reviewed or endorsed this website.
Related guides
Educational guidance cannot diagnose an individual fish. Breathing distress, severe injury or unexplained losses need prompt professional assessment.