Koi Aeromonas Bacterial Infection Treatment Guide: Salt and Antibiotic

Aeromonas is the bacterial menace that turns a healthy 60 cm koi into an ulcer-ridden patient within 7-14 days if left untreated. The koi aeromonas treatment protocol combines water quality correction, salt therapy, topical wound care, and antibiotic injection where ulcers are advanced. This guide from Gensou Aquascaping at 5 Everton Park covers diagnosis, the staged treatment ladder, and the Singapore koi vet network that supports serious cases. Aeromonas hits hard in tropical climates because warm water (28-31°C) accelerates bacterial replication.

Identifying Aeromonas Symptoms

Early signs: red patches on flanks, fin base hyperemia, slight fin clamp, slowing appetite. Mid-stage: small ulcerations (2-5 mm) with raised inflamed edges, scale loss around the ulcer, secondary fungus on damaged tissue. Late stage: deep ulcers (10-30 mm) penetrating to muscle, septicaemia (red streaks along the lateral line), bilateral exophthalmia (popeye), abdominal swelling. Aeromonas salmonicida and Aeromonas hydrophila are the two most common Singapore strains.

Water Quality as First Response

Aeromonas almost always emerges from underlying water quality stress — high ammonia, low dissolved oxygen, temperature spikes, or organic overload. Test water immediately: ammonia, nitrite, nitrate, pH, KH, dissolved oxygen. Run a 30-50 per cent water exchange with conditioner from the water care and treatment shelf. Increase aeration. Bring water back to clean parameters before any treatment will work.

Salt Therapy Protocol

Bath salt at 0.3-0.5 per cent (3-5 g per litre) supports osmotic stability while the fish heals. Add the salt gradually over 24 hours — never dose all at once. Use pure non-iodised aquarium salt; iodised table salt damages biofiltration. Maintain salt level for 7-14 days, then dilute back through partial water exchanges. Salt also reduces external parasites that often piggyback aeromonas.

Topical Wound Treatment

For visible ulcers, sedate the koi (clove oil at 30 ppm or MS-222 at 100 ppm) and clean each ulcer with sterile cotton swabs. Apply povidone iodine (Betadine) directly to the ulcer base, then a sealing layer of waterproof topical (Orabase, Tricide-Neo, or specialist koi wound powder). The seal protects the tissue while it heals. Repeat topical treatment every 3-5 days until granulation tissue forms.

Antibiotic Injection

Mid- to late-stage aeromonas requires intramuscular antibiotic injection. Oxytetracycline at 25 mg per kg body weight, injected into the dorsal musculature, repeated every 72 hours for 3-5 doses, is the standard protocol. Romet (sulfa-trimethoprim) at 50 mg per kg for 5 days is an alternative. Both require veterinary prescription in Singapore. Costs run SGD 150-300 per vet visit, plus medication. Singapore koi vets include AquaVet Singapore, Mount Pleasant After Hours, and specialist fish vets at C328 referral network.

Quarantine and Isolation

Move the affected fish to a separate 200-500 litre quarantine tub during treatment. The tub runs sponge-baffled aeration, light filtration, and salt at 0.3 per cent. Daily 25 per cent water changes. Treatment runs 14-30 days depending on ulcer severity. Returning the fish to the main pond too early triggers re-infection. Stock from the aquarium equipment range covers quarantine tub equipment.

Prevention Through Husbandry

Aeromonas prevention is identical to general koi health hygiene. Maintain water quality (ammonia and nitrite zero, nitrate under 40 ppm, pH stable, KH 5-7). Avoid overstocking. Quarantine all new fish for 30 days minimum. Feed quality protein from the fish food and feeding range. Monitor body language daily — early appetite changes flag underlying stress before bacterial outbreaks emerge.

When to Euthanise

If ulcerations cover more than 30 per cent of body surface, septicaemia is established (red streaks along the lateral line), or the fish stops eating despite 7+ days of treatment, prognosis is poor. Humane euthanasia uses clove oil overdose (300-500 ppm) followed by ice water immersion. Singapore koi vets can perform euthanasia for SGD 80-150. Document the loss with photographs for any insurance claim.

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