25/08/2026
Aeromonas infection in koi is a serious bacterial condition that typically arises when fish are subjected to stress, poor water quality, injuries, overcrowding, oxygen depletion, or drastic temperature fluctuations. Symptoms include red patches, hemorrhaging, damaged fins, raised scales, and even deep ulcers.
🐟 How to treat koi affected by Aeromonas
1. Immediately quarantine the sick koi Move the fish to a quarantine tank with strong aeration. This facilitates treatment and minimizes the risk of the disease spreading to other koi.
2. Improve water quality first This is crucial. Check the following: Ammonia Nitrite pH Temperature Dissolved oxygen Aeromonas often becomes a problem when koi are stressed due to poor water quality or unstable environmental conditions. Perform a partial water change using safe (dechlorinated) water, remove waste and leftover food, and ensure the biological filter is functioning correctly.
3. Avoid mixing multiple medications indiscriminately Antibiotics should be selected based on a diagnosis and, if possible, bacterial sensitivity testing. Different strains of Aeromonas may respond differently to medication, and indiscriminate antibiotic use can lead to resistance.
4. Treat wounds or ulcers specifically Aeromonas can cause deep ulcers. For external wounds, topical treatment can be used on ornamental fish, provided the right products and application methods are chosen.
5. Consult a fish veterinarian for antibiotic treatment For severe infections—such as when the koi stops eating, ulcers deepen, the abdomen swells, hemorrhaging occurs, or fish begin to die—consult a veterinarian specializing in fish. In bacterial cases, antimicrobial therapy may be necessary, but the medication and dosage must be tailored to the fish's condition.
⚠️ Common reasons for treatment failure Do not treat the fish while ignoring underlying pond issues. Poor water quality, stress, and existing wounds or parasites can cause recurring Aeromonas infections. Improving water quality and addressing sources of stress are essential parts of the treatment process.
