When koi exhibit abnormal behavior, it is often an early sign of health issues. Below is a correspondence table of common symptoms and their potential causes:
I. Abnormal Surface Behavior (Commonly Parasite‑Related)
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Abnormal Behavior
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Possible Problem
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Additional Notes
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|---|---|---|
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Frequent body‑rubbing, scraping the bottom
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External parasites (Dactylogyrus, Trichodina, etc.)
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Obvious itching; often accompanied by increased mucus.
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Flicking fins, clamped fins
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Initial stage of external parasites or bacterial infection
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Fin bases may appear reddened or congested.
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Body shaking, jumping
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Anchor worm (Lernaea) or fish lice bites
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Visible parasites may be attached in severe cases.
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White spots, cotton‑like growths
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Ichthyophthirius multifiliis(ich) or saprolegnia
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Requires timely isolation and treatment.
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II. Abnormal Swimming Posture (Watch for Gill or Internal Issues)
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Abnormal Behavior
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Possible Problem
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Additional Notes
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|---|---|---|
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Swimming against the current at the outlet
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Gill parasites or gill rot
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Difficulty breathing; seeks high‑oxygen flow.
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Staying still in corners, sluggish response
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Gill disease, enteritis, or poisoning
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Often accompanied by loss of appetite.
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Head‑down tilt
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Swim‑bladder disorder, enteritis, or internal organ problems
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Loss of balance; fasting is recommended for observation.
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Tail up, sideways swimming
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Swim‑bladder disorder, dropsy, or parasites
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Swimming posture becomes unbalanced.
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Gasping at surface, rapid breathing
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Hypoxia, gill disease, or water‑quality deterioration
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Especially dangerous during early morning hours.
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III. Other Abnormal Signs
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Symptom
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Possible Cause
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|---|---|
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Sudden loss of appetite
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Enteritis, internal parasites, sudden water‑quality change
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Darkening or blackening of body color
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Stress, poisoning, or chronic illness
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Isolating from the group
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Weakness, illness, or being bullied
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Abnormal feces (white, stringy)
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Enteritis, indigestion
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IV. Emergency Response Recommendations
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Observe first, do not medicate blindly: Record the frequency, timing, and number of affected fish.
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Test water quality: Immediately check pH, ammonia, and nitrite levels to rule out water‑quality issues.
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Isolate sick fish: If symptoms are obvious, promptly move the fish to an isolation tank for observation.
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Treat according to the cause: Based on the symptoms, determine the likely cause and choose gentle treatment (e.g., begin with a salt‑bath observation).
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Consult experienced keepers: Take photos or videos and seek advice from local professionals.
