Channel catfish virus disease

Signs of disease

Important: animals with disease may show one or more of the signs below, but disease may still be present in the absence of any signs.

Disease signs at the farm level

• high mortality in fry and juvenile catfish

Disease signs at the tank and pond level

• occurs in fry and fingerlings less than a year old and less than 15 cm long, in the hatchery and in ponds
• first sign is a slowing of feeding activity
• erratic swimming, often in an aimless spiral pattern
• possible brief episodes of hyperactivity when fish are disturbed, followed by long periods of lethargy
• ultimately, possible large congregations of fish at sides of hatching troughs or ponds, motionless in a head-up, tail-down position
• mortality

Clinical signs of disease in an infected animal

• ascites (swollen abdomen from accumulated fluid)
• exophthalmus (pop eye)
• haemorrhaging of fins, on the ventral abdomen, and within muscle tissue

Gross signs of disease in an infected animal

• haemorrhaging of muscle
• extensive necrosis of renal tubules and interstitial tissues of the kidney
• spleen often dark and enlarged

Disease agent

Channel catfish virus disease (CCVD) is caused by a herpesvirus (Ictalurid herpesvirus 1).

Host range

Fish known to be susceptible to CCVD:

* naturally susceptible (other species have been shown to be experimentally susceptible)

Presence in Australia

EXOTIC—not present in Australia.

Epidemiology

• Horizontal transmission occurs directly from virus shed in water, and from virus carried by animate vectors and on fomites.
• Vertical transmission is believed to be common. However, because no infectious virus has been found on the skin or sexual products at spawning, this mechanism has not been proven.
• Survivors of CCVD remain covert carriers of the virus.
• Susceptibility appears to vary according to the strain of channel catfish.
• Although older fish are susceptible to outbreaks of the CCVD, the disease occurs almost exclusively in fish that are less than one year old, and generally in fish less than four months old.
• Mortality is highest where water temperature exceeds 27^oC, but decreases with temperature and ceases at 18^oC.

Differential diagnosis

The differential diagnostic table and the list of similar diseases appearing at the bottom of each disease page refer only to the diseases covered by this field guide. Gross signs observed might well be representative of a wider range of diseases not included here. Therefore, these diagnostic aids should not be read as a guide to a definitive diagnosis, but rather as a tool to help identify the listed diseases that most closely account for the gross signs.

Similar diseases

Enteric septicaemia of catfish

Sample collection

Because of uncertainty in differentiating diseases using only gross signs, and because some aquatic animal disease agents might pose a risk to humans, you should not try to collect samples unless you have been trained. Instead, you should phone your state or territory hotline number and report your observations. If samples have to be collected, the agency taking the call will advise you on what you need to do. Local or district fisheries/veterinary authorities could advise you on sampling.

Emergency disease hotline

For your state or territory emergency disease hotline number, see Whom to contact if you suspect a disease.

Further reading

The currently accepted procedures for a conclusive diagnosis of CCVD are summarised at www.oie.int/eng/normes/fmanual/A_00023.htm