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Protozoan Diseases in Fishes

Protozoan Diseases in Fishes  

a. Whirling Disease:

  • This disease is caused by a myxosporidian protozoan, Myxosoma cerebralis only in salmon fishes.
  • The symptoms are pancreatic necrosis, lesions and disintegration of the cartilaginous skeletal support of the organ of equilibrium.
  • Rapid tail-chasing type of whirling is often seen when the fish is frightened or trying to feed.
  • The typical symptoms usually appear at 1-2 months after exposure to the disease.
  • If the pond contains all infected fish, it is better to destroy them by deep burial. Then the pond should be cleaned thoroughly and disinfected with calcium cyanamide, quick lime or sodium hypochlorite.

b. Costiasis Disease:

  • This is caused by a mastigophore - Costia necatrix in culture fishes.
  • This is a common disease in ponds where fishes live densely in water with a low pH and poor condition food.
  • The parasites live in large numbers on fish skin, fins and gills. The symptoms are appearance of grey blue film on the skin which turns to red patches in severely affected cases.
  • The infected fish becomes weak; loss of appetite occurs and finally dies.
  • They can be treated with 3% common salt for 10 minute or 1: 2500 formalin solution.

c. Ichthyophthiriasis Disease:                                                                  

  • This caused by a ciliate, Ichthyophthirius multifilis.
  • This disease is also called as “Ich” or “White Spot Disease”.
  • The young parasites moving in water get attached to the skin of the fish. They grow between the epidermis and dermis and after becoming large in size fall to the bottom of the pond.
  • Infected fish develop small white spots on the skin and the fins.
  • These parasites attack the gills also. Fish respond by jumping in the water and rubbing their body against the objects in the pond. Respiration gets affected and they finally die.
  • Dip treatment in 1.5 ppm of malachite green or in 10 ppm of acriflavin gives good results.
  • 3% salt solution, 1:4,000 formalin, 1:1, 00,000 quinine hydrochloride, 1:5,00,000 methyl blue are also useful to treat the fish.


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