Skip to content

Bacterial dropsy and tail rot (Aeromonas) in carps Photo: Krishnendu Biswas · Pexels License · source ↗

Bacterial dropsy and tail rot (Aeromonas) in carps

Bacterial dropsy and tail/fin rot in cultured Indian Major Carps and exotic carps are caused primarily by motile Aeromonas hydrophila (and related A. veronii, A. sobria) — opportunistic gram-negative bacteria that are ubiquitous in freshwater pond mud and water. Outbreaks typically follow physical injury, parasite infestation, water-quality stress, or temperature-extreme handling.

Identification

The complex includes several presentations under common names:

  • Dropsy (motile aeromonad septicaemia): fluid accumulation in body cavity, pop-eye (exophthalmia), scale protrusion (pine-cone appearance), reddened vent, lethargy
  • Tail and fin rot: erosion of fin margins beginning as a white border, progressing to ragged necrosis exposing fin rays
  • Skin ulcer disease: shallow reddish lesions on flanks that deepen into open ulcers
  • Haemorrhagic septicaemia: petechial haemorrhages on body, fin bases and visceral organs; sudden mortality

Hosts and triggers

All cultured carps — rohu, catla, mrigal, calbasu, common carp, silver carp, grass carp — are susceptible. Outbreaks are commonly triggered by argulosis (Carp Disease Argulus Anchor Worm) creating entry wounds, low dissolved oxygen, sudden temperature drops, transport stress, overcrowding, and high organic load with elevated ammonia. The bacterium is endemic in pond systems; disease emerges when host immunity is compromised.

Economic impact

Bacterial dropsy outbreaks can kill 30-60% of stock within 7-14 days if untreated. The disease is the second most important cause of crop loss in Indian carp polyculture after EUS, with regular outbreaks during monsoon onset and post-monsoon temperature drops.

Management

  • Pond preparation: complete drying, sun-exposure and liming at 250-500 kg/ha between cycles
  • Water-quality: maintain dissolved oxygen above 4 mg/L, control ammonia by water exchange and aeration, avoid sudden temperature swings
  • Stress reduction: avoid overstocking, handle gently during netting, quarantine new fingerlings
  • Chemical control during outbreak: lime application 50-100 kg/ha; potassium permanganate bath at 2-5 ppm; salt bath at 1-3% for 5-10 minutes
  • Antibiotic treatment (under veterinary advice only): oxytetracycline or florfenicol incorporated in feed at recommended dose; full withdrawal period before harvest
  • Vaccines: experimental autogenous Aeromonas vaccines are available for high-value systems
  • Address primary cause: treat argulosis, improve aeration, lower stocking density

See also: Rohu Labeo Rohita Imc, Catla Catla Indian Major Carp, Mrigal Cirrhinus Mrigala Imc, Carp Disease Argulus Anchor Worm, Fish Pond Construction.

Sources

  1. Bacterial dropsy in cultured carps. ICAR-CIFA Bhubaneswar.
  2. Aeromonas hydrophila infections in aquaculture. NACA.
  3. Fish health and disease management. Vikaspedia.