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Diseases

KHV — Koi Herpesvirus

Pathogen: Cyprinid herpesvirus 3 (CyHV-3) Affected species: Koi and common carp (NOT goldfish) Symptoms:

  • Sudden mass mortality (can kill 80–100% of the fish in the pond)
  • Necrotic gills, hemorrhages
  • Erratic behavior, lethargy
  • Activation temperature: 16–25°C (does not appear in cold temperatures < 13°C or hot temperatures > 30°C)

Treatment: There is no treatment. This disease is a notifiable disease in many countries. Prevention: Strictly quarantine all new koi (at least 4–6 weeks at 18–22°C); purchase only from certified suppliers; never mix koi from different sources without quarantining them first.

SVC — Spring Viraemia of Carp

Pathogen: Rhabdovirus carpio Species: Carp, koi, goldfish Symptoms: Most common in the spring (10–17°C). Ascites, hemorrhages, exophthalmos, lethargy. High mortality rate. Treatment: There is no treatment. Reporting is required. Prevention: Quarantine; avoid water from rivers and natural ponds that has not been disinfected.

Trichodina and gill parasites

It is more common in the spring when temperatures rise and the fish are weakened after the winter. Symptoms: Scratching, excessive mucus, "flashing" (rapid side-to-side movement) Treatment: Rock salt (2–3 g/L), formalin + malachite green, Chinosol

Lernaea (anchor worm)

Appearance: 1–2 cm worms visible embedded in the skin, with a red, inflamed area Treatment: Manual removal with tweezers; DIMILIN or Trichlorfon added to the water (copepod life cycle)

Argulus (fish louse)

Appearance: A flat, circular parasite, 5–10 mm in size, visible to the naked eye and moving across the skin Treatment: Manual removal; DIMILIN; Azamethylphosphate (Salmosan)

Bacterial Ulcers (Aeromonas)

Very common in ponds in the spring after winter, when the fish are immunocompromised. Symptoms: Deep ulcers, redness, flaking skin Treatment: Systemic antibiotic (oxytetracycline in medicated feed), cleaning the ulcer with an antiseptic (iodine, chloramine-T), improving water quality.

Pond Algae

Green water (phytoplankton): A UV sterilizer solves the problem in 3–5 days. Filamentous algae (blanket weed, Cladophora): Remove manually with a stick; plant Black Barley; increase the number of floating plants to create competition.