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Chapter: Health Management in Aquaculture: Viral diseases

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Grass Carp Hemorrhagic Disease - Viral Infections In Fish

Grass carp (Ctenopharyngodon idellus), black carp (Mylopharyngodon piceus), topmouth gudgeon (Pseudorasbora parva), silver carp (Hypophthalmichthysmolitrix), Chinese minnow (Hemiculter bleekeri) and rare minnow (Gobiocypris rarus).

Grass Carp Hemorrhagic Disease

CAUSATIVE AGENT:

Aquareovirus (60 to 80 nm)

SPECIES AFFECTED:

Grass carp (Ctenopharyngodon idellus), black carp (Mylopharyngodon piceus), topmouth gudgeon (Pseudorasbora parva), silver carp (Hypophthalmichthysmolitrix), Chinese minnow (Hemiculter bleekeri) and rare minnow (Gobiocypris rarus)

GROSS SIGNS:

Clinical signs include exophthalmia, hemorrhagic or pale gills and hemor-rhagic fin bases or gill covers.

EFFECT ON HOST:

This disease was first observed in China more than 20 years ago. Outbreaks occured in Southern China during the summer at temperatures of 24-30°C. Acute infections cause significant mortalities of up to 80% among fingerlings and sometimes among yearlings. Internally, hemorrhages occur in the muscu-lature, oral cavity, intestinal tract, liver, spleen and kidneys. Naturally and ex-perimentally infected fish manifest reduced erythrocytes, plasma protein, cal-cium and urea nitrogen. Serum potassium elevated. Signs of disease and mor-tality are observed within 1 to 2 weeks of exposure of fish in water at tempera-tures of 25°C or higher. Experimental vaccination induced 80% level of immu-nity by day 4 at temperatures above 20°C.

DIAGNOSIS:

The virus can be propagated in cell cultures of GCK-84, GCG and GCF yielding titers as high as 108 to 109TCID50 per ml. In vitro replication is considered opti-mum between 28 and 30°C inducing CPE in 3 to 4 days post inoculation. Re-verse transcription-polymerase chain reaction (RT-PCR) and electron micros-copy are also used for detecting the virus.


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