Articles for Vets Diseases of Animals Diseases of Fishes

Saprolegniasis: Diagnosis & Treatment

Saprolegniasis

Saprolegniasis is a fungal disease of fish and fish eggs most commonly caused by the Saprolegnia species called “water molds.” They are common in fresh or brackish water.

Lesions

  • focal grey-white patches on the skin which have a cotton wool-like appearance under water when the hyphal elements extend out. The early lesions are circular and extend out until they merge.
  • The patches can then become dark grey or brown as the mycelium traps mud or debris.
  • The head region is most commonly involved, but any part of the skin or gills, even internal organs, can be affected.
  • Respiratory distress may be evident if the gills are involved, and death can follow rapidly.

Diagnosis

  • The clinical signs are quite characteristic.
  • Skin scrapes examined under the microscope may help identify the fungal hyphae which belong to Saprolegnia.
  • Histopathology reveals: the fungus invading the stratum spongiosum of the dermis and then the epidermis, causing erosions as it spreads. 

Treatment

  • Salt: 1–5g / litre indefinitely
  • Malachite green: 0.10mg/litre – three treatments at three-day intervals
  • Potassium permanganate at 3-4 ppm every fourth day for four treatments with hydrogen peroxide reversal.

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