Observe the individual koi and the whole group before focusing on pattern. Normal appearance is encouraging, but it cannot rule out all infection or predict future health. Combine a visual check with seller records and a separate quarantine plan.
Observe Without Disturbing the Fish
Watch before food is offered or fish are chased. Compare breathing, swimming balance, fin posture, and the behavior of neighboring fish. A shy koi is not automatically sick, and an eager feeder is not automatically free of disease. Temperature, recent handling, and individual behavior affect what you see.
Inspect Visible Features
- Look for open lesions, swelling, unusual mucus, or new visible growths.
- Check fin integrity and the fish's ability to swim upright and turn smoothly.
- Compare the two eyes and note recent asymmetry or cloudiness.
- View the sides as well as the back; recognize Doitsu scaling and normal pattern differences.
Separate Pattern from Health
Bright color, strong metallic shine, or even scales may be attractive, but no decorative feature proves health. Do not ask for gill covers to be lifted simply to complete a shopping checklist. A fish with a concerning finding needs explanation and assessment, not a quick reassurance that its pattern is valuable.
Ask for a Useful History
Request source and holding details, new-group mixing, treatments, previous losses, and any testing with its date and scope. A seller should distinguish confirmed findings from estimates. Save current individual photographs and a video, especially when buying remotely.
When to Walk Away or Wait
Postpone if persistent breathing trouble, loss of balance, an expanding lesion, or unexplained group illness is present. Unresolved concerns deserve professional assessment. Use seller comparison and prepare quarantine before arranging the arrival.