Aeromonad Septicemia: symptoms, treatment, prevention

Aeromonas hydrophila is an opportunistic Gram-negative bacterium ubiquitous in freshwater that causes hemorrhagic septicemia in stressed or wounded fish.

Overview

Motile Aeromonad Septicemia is caused by Aeromonas hydrophila, a Gram-negative bacterium present in almost all freshwater systems. It causes systemic disease in stressed or wounded fish, with hemorrhagic ulcers, dropsy and rapid mortality; the disease is fatal if untreated.

Symptoms

Red ulcers on the body
Raised scales (pineconing) in advanced cases
Swollen abdomen
Popeye
Fin rot
Lethargy and rapid death

Causes

High ammonia or nitrite, physical injuries, transport stress, sudden temperature changes and overcrowding allow the bacterium to overwhelm fish defences.

Diagnosis

Hemorrhagic ulcers with pineconing and abdominal swelling are characteristic. Definitive diagnosis requires bacterial culture; clinically rule out columnaris (fungus-like lesions on mouth) and viral causes.

Treatment

Combine an antibiotic course with strict water-quality correction. Severe cases need a fluoroquinolone administered by a fish veterinarian.

Quarantine

Move affected fish to a hospital tank with strong filtration and aeration. Disinfect nets and equipment used in the original tank.

Medication

Aminoglycoside (kanamycin sulfate) combined with a nitrofuran derivative (such as nitrofurazone) in quarantine for 7-10 days, in food where possible.
Fluoroquinolone (ciprofloxacin or enrofloxacin) at 5-10 mg/kg fish, given by veterinary injection or in medicated food, for severe cases.

Recovery

Continue large water changes and high-quality feeding after the antibiotic course. Address the underlying stress or water quality issue that triggered the outbreak.

Prevention

Minimise physical injury and stress
Maintain stable water quality
Keep ammonia and nitrite at zero
Quarantine new fish
Feed a balanced diet to support immunity