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Ornamental Fish Q&A 09 (view source)

Revision as of 12:16, 22 September 2011

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<FlashCard questions="1">
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<FlashCard questions="3">
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|q1=Discuss methods of euthanasia recommended to professional fisheries personnel as well as home hobbyists.
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|q1=Describe the disease condition illustrated by the photograph.
 
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Veterinarians often must recommend to a client that a fish be euthanatized.  
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The photograph shows a discrete, oval, raised, plaque-like lesion on the gill of a koi carp recently imported to the UK from Japan.
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These changes were consistent with a diagnosis of branchiomycosis (gill rot), which is a disease of freshwater fish caused by
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the fungus ''Branchiomyces''.  
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Several methods of fish euthanasia are approved by the American Veterinary Medical Association
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It has been described in Europe, Japan, India, and parts of the USA.  
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(AVMA) including:
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*cranial concussion followed by decapitation;
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*cervical dislocation followed by double pithing (both the brain and spinal cord);
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*chemical overdose.  
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If available, tricaine methanesulfonate (TMS) at a dose of 300–500 p.p.m. for 15 minutes will kill most fish.  
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Spores attach to the gill surface and germinate to form hyphae. These hyphae proliferate, causing damage to the blood supply and necrosis. Sloughing of this necrotic tissue releases spores into the water, which then continue to develop on the floor of the pond or aquarium if conditions are favorable (i.e. temperatures of 25–32°C (77.0–89.6°F), high levels of organic material, low oxygen levels, and a low pH).
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|q2=What tests can be performed to confirm the diagnosis?
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The diagnosis of branchiomycosis could be confirmed by examining fresh scrapings taken from the lesion and by histopathology.  
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Since most hobbyists and veterinary clinics do not have TMS on hand, alternatives include benzocaine hydrochloride, oil of cloves, and even carbon dioxide in the form of antacid tablets (2–3 tablets/L of water).  
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In this particular case, the scraping would be expected to yield branched aseptate hyphae.  
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Injectable sodium pentobarbital (60 mg/kg) given IV or IP is another chemical alternative for larger fish.  
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Large areas of necrosis containing fungal spores and hyphae can usually be seen on histopathology with a GMS (Gomori methenamine silver) preparation.
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|q3=How is the organism transmitted, and what measures would you advise to treat and prevent the problem?
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Fungal spores can be introduced directly by adding infected or carrier fish, or indirectly by birds or the use of raw fish products.
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As a last resort, a client in a remote location can use ethanol at a final concentration of 10%.  
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Treatment is generally unrewarding, although 2-phenoxyethanol has been suggested.
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Veterinarians should consider offering a euthanasia service since many clients are attached to their fish pets.
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Control is achieved by good hygiene, avoiding the use of raw fish products, and adequate quarantine of all new fish to avoid introduction of the organism.
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HelenD
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